The Crystal Structure of the Human (S100A8/S100A9)2 Heterotetramer, Calprotectin, Illustrates how Conformational Changes of Interacting α-Helices Can Determine Specific Association of Two EF-hand Proteins

Calprotectin-Mediated Zinc Chelation Inhibits Pseudomonas aeruginosa Protease Activity in Cystic Fibrosis Sputum

Pseudomonas aeruginosa induces pathways indicative of low zinc availability in the cystic fibrosis (CF) lung environment. To learn more about P. aeruginosa zinc access in CF, we grew P. aeruginosa strain PAO1 directly in expectorated CF sputum. The P. aeruginosa Zur transcriptional repressor controls the response to low intracellular zinc, and we used the NanoString methodology to monitor levels of Zur-regulated transcripts, including those encoding a zincophore system, a zinc importer, and paralogs of zinc containing proteins that do not require zinc for activity. Zur-controlled transcripts were induced in sputum-grown P. aeruginosa compared to those grown in control cultures but not if the sputum was amended with zinc. Amendment of sputum with ferrous iron did not reduce expression of Zur-regulated genes. A reporter fusion to a Zur-regulated promoter had variable activity in P. aeruginosa grown in sputum from different donors, and this variation inversely correlated with sputum zinc concentrations. Recombinant human calprotectin (CP), a divalent-metal binding protein released by neutrophils, was sufficient to induce a zinc starvation response in P. aeruginosa grown in laboratory medium or zinc-amended CF sputum, indicating that CP is functional in the sputum environment. Zinc metalloproteases comprise a large fraction of secreted zinc-binding P. aeruginosa proteins. Here, we show that recombinant CP inhibited both LasB-mediated casein degradation and LasA-mediated lysis of Staphylococcus aureus, which was reversible with added zinc. These studies reveal the potential for CP-mediated zinc chelation to posttranslationally inhibit zinc metalloprotease activity and thereby affect the protease-dependent physiology and/or virulence of P. aeruginosa in the CF lung environment. IMPORTANCE The factors that contribute to worse outcomes in individuals with cystic fibrosis (CF) with chronic Pseudomonas aeruginosa infections are not well understood. Therefore, there is a need to understand environmental factors within the CF airway that contribute to P. aeruginosa colonization and infection. We demonstrate that growing bacteria in CF sputum induces a zinc starvation response that inversely correlates with sputum zinc levels. Additionally, both calprotectin and a chemical zinc chelator inhibit the proteolytic activities of LasA and LasB proteases, suggesting that extracellular zinc chelators can influence proteolytic activity and thus P. aeruginosa virulence and nutrient acquisition in vivo.

Circulating calprotectin as biomarker in neutrophil-related inflammation: Pre-analytical recommendations and reference values according to sample type

BACKGROUND

Calprotectin (CLP) is a promising biomarker for the evaluation of neutrophil-related inflammation. Our aim was to establish reference values for circulating CLP in different sample types and to study the effect of pre-analytical variables.

METHODS

Reference values were determined in 100 healthy individuals. Pre-analytical variables were evaluated in 10 healthy controls and four rheumatoid arthritis patients with active disease and covered sample type (serum with/without gel separator, heparin, EDTA and citrate plasma), pre-centrifugation time (<2 h, 6 h, 24 h), storage condition (2-8 °C, 18-25 °C, 30 °C) and storage time (24 h, 72 h, 7 days). CLP measurements were performed with the EliA™Calprotectin 2 assay on Phadia™200 (Thermo Fisher Scientific).

RESULTS

In healthy controls, baseline CLP concentrations in serum were more than double the concentration in EDTA and citrate plasma (0.909 µg/mL versus 0.259 µg/mL and 0.261 µg/mL respectively). Heparin, EDTA and citrate stabilized CLP concentrations for up to 6 h before centrifugation, whereas significant increases in CLP levels were observed when serum was left untreated during that time period.

CONCLUSION

Clinical studies on circulating CLP need to apply sample type-specific reference values and decision limits. To obtain reproducible CLP results in serum, more stringent pre-analytical sample handling instructions are needed.

Microheterogeneity and preanalytical stability of protein biomarkers of inflammation and renal function

Protein biomarker microheterogeneity has attracted increasing attention in epidemiological and clinical research studies. Knowledge concerning the preanalytical stability of proteins is paramount to assess the biological significance of their proteoforms. We investigated the stability of the inflammatory markers C-reactive protein (CRP), serum amyloid A (SAA), and calprotectin (S100A8/9), and the renal function marker, cystatin C (CnC). In total 16 proteoforms were quantified by immuno-MALDI-TOF MS in EDTA plasma and serum samples from 15 healthy volunteers. Prior to analysis blood samples were stored at either room temperature from 1 h up to 8 days, or underwent up to 9 consecutive freeze/thaw cycles. Pearson's correlation coefficient and t-test, intra-class correlation coefficient (ICC), and Autoregressive Integrated Moving-Average (ARIMA) models were used to investigate the stability of proteoform concentrations and distributions in blood. Plasma and serum concentrations of CRP and SAA proteoforms were highly stable during room temperature exposure and repeated freeze/thaw cycles, demonstrating excellent reproducibility (ICC > 0.75), no serial dependency in ARIMA models, and stable distribution of proteoforms. Stability analyses for proteoforms of S100A8/9 and CnC identified only minor preanalytical changes in concentrations and distributions, and none of the proteoforms were produced during prolonged exposure to room temperature or repeated freezing/thawing. The four proteins and their proteoforms are stable during sub-optimal sample handling, and represent robust biomarker candidates for future biobank studies aimed at investigating the microheterogeneity of SAA, S100A8/9, and CnC in relation to inflammation, renal dysfunction and various clinical outcomes.

Deletion of S100a8 and S100a9 Enhances Skin Hyperplasia and Promotes the Th17 Response in Imiquimod-Induced Psoriasis

High concentrations of the damage-associated molecular patterns S100A8 and S100A9 are found in skin and serum from patients suffering from psoriasis, an IL-17-related disease. Notably, although the expression of these proteins correlates with psoriatic disease severity, the exact function of S100A8 and S100A9 in psoriasis pathogenesis remains unclear. In this study, we investigated the role of S100A8 and S100A9 in psoriasis-associated skin hyperplasia and immune responses using S100a8-/- and S100a9-/- mice in an imiquimod-induced model of psoriasis. We found that S100a8-/- and S100a9-/- psoriatic mice exhibit worsened clinical symptoms relative to wild-type mice and increased expression of S100A9 and S100A8 proteins in keratinocytes, respectively. In addition, the loss of S100A8 enhances proliferation of keratinocytes and disrupts keratinocyte differentiation. We further detected elevated production of IL-17A and -F from CD4+ T cells in the absence of S100A8 and S100A9, as well as increased infiltration of neutrophils in the skin. In addition, treatment with anti-IL-17A and -F was found to reduce psoriasis symptoms and skin hyperplasia in S100a8-/- and S100a9-/- mice. These data suggest that S100A8 and S100A9 regulate psoriasis by inhibiting production of IL-17A and -F, thereby, to our knowledge, providing new insights into their biological functions.

Faecal Biomarkers in Inflammatory Bowel Diseases: Calprotectin Versus Lipocalin-2-a Comparative Study

BACKGROUND AND AIMS

Faecal biomarkers, particularly calprotectin [FCAL], have become important diagnostic and monitoring tools in inflammatory bowel diseases [IBD]. As FCAL is mainly produced by neutrophils, we hypothesised that faecal lipocalin-2 [FLCN2], also expressed by intestinal epithelial cells [IEC], could be beneficial in specific clinical situations.

METHODS

We compared clinical and endoscopic activity-related correlations between FCAL and FLCN2, assayed from the same sample, in a cohort of 132 patients (72 Crohn's disease [CD]) and 40 controls. A detailed analysis of cellular origins was done by confocal microscopy and flow cytometry. To evaluate the potential to detect low-grade inflammation, we studied faecal and tissue concentrations in a cohort with clinical, endoscopic, and histological remission.

RESULTS

There was an excellent correlation between FCAL and FLCN2 [rS = 0.87, p <0.001] and comparable sensitivity and specificity to predict clinical and endoscopic disease activity, with optimal thresholds for endoscopic activity of 73.4 and 1.98 µg/g in ulcerative colitis [UC] and 78.4 and 0.56 µg/g in Crohn's disease for FCAL and FLCN2, respectively. Strong co-expression of both proteins was observed in granulocytes and macrophages. IECs expressed LCN2 but not CAL. In our IBD cohort in deep remission neither FCAL nor FLCN2 was different from controls; yet mucosal LCN2 but not CAL expressions remained elevated in the rectum of UC and the ileum of CD patients.

CONCLUSIONS

This study corroborates the diagnostic equivalence of FLCN2 and FCAL in IBD. In remission, persistent mucosal overexpression renders LCN2 an attractive candidate for molecular inflammation warranting further investigation.

Divalent cations influence the dimerization mode of murine S100A9 protein by modulating its disulfide bond pattern

S100A9, with its congener S100A8, belongs to the S100 family of calcium-binding proteins found exclusively in vertebrates. These two proteins are major constituents of neutrophils. In response to a pathological condition, they can be released extracellularly and become alarmins that induce both pro- and anti-inflammatory signals, through specific cell surface receptors. They also act as antimicrobial agents, mainly as a S100A8/A9 heterocomplex, through metal sequestration. The mechanisms whereby divalent cations modulate the extracellular functions of S100A8 and S100A9 are still unclear. Importantly, it has been proposed that these ions may affect both the ternary and quaternary structure of these proteins, thereby influencing their physiological properties. In the present study, we report the crystal structures of WT and C80A murine S100A9 (mS100A9), determined at 1.45 and 2.35 Å resolution, respectively, in the presence of calcium and zinc. These structures reveal a canonical homodimeric form for the protein. They also unravel an intramolecular disulfide bridge that stabilizes the C-terminal tail in a rigid conformation, thus shaping a second Zn-binding site per S100A9 protomer. In solution, mS100A9 apparently binds only two zinc ions per homodimer, with an affinity in the micromolar range, and aggregates in the presence of excess zinc. Using mass spectrometry, we demonstrate that mS100A9 can form both non-covalent and covalent homodimers with distinct disulfide bond patterns. Interestingly, calcium and zinc seem to affect differentially the relative proportion of these forms. We discuss how the metal-dependent interconversion between mS100A9 homodimers may explain the versatility of physiological functions attributed to the protein.

Toll-Like Receptors, Associated Biochemical Signaling Networks, and S100 Ligands

ABSTRACT

Host cells recognize molecules that signal danger using pattern recognition receptors (PRRs). Toll-like receptors (TLRs) are the most studied class of PRRs and detect pathogen-associated molecular patterns and danger-associated molecular patterns. Cellular TLR activation and signal transduction can therefore contain, combat, and clear danger by enabling appropriate gene transcription. Here, we review the expression, regulation, and function of different TLRs, with an emphasis on TLR-4, and how TLR adaptor protein binding directs intracellular signaling resulting in activation or termination of an innate immune response. Finally, we highlight the recent progress of research on the involvement of S100 proteins as ligands for TLR-4 in inflammatory disease.

Global Studies of Using Fecal Biomarkers in Predicting Relapse in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the gastrointestinal tract mainly comprising two forms including Crohn's disease (CD) and ulcerative colitis (UC). IBD is a lifelong relapsing remitting disease and relapses occur at random patterns which are unpredictable. Fecal biomarkers have been increasingly used to assess disease activity in IBD due to their positive correlations with intestinal inflammation. Recent studies have also assessed the use of fecal biomarkers in predicting relapse and post-operative recurrence. This review provides information from global studies of using fecal calprotectin, lactoferrin and S100A12 to predict relapse in IBD. Strategies for further studies and the use of these fecal biomarkers for personalized management in IBD are also discussed.

The Influence of Solvent on the Crystal Packing of Ethacridinium Phthalate Solvates

The synthesis, structural characterization and influence of solvents on the crystal packing of solvated complexes of ethacridine with phthalic acid: 6,9-diamino-2-ethoxyacridinium phthalate methanol solvate (1), 6,9-diamino-2-ethoxyacridinium phthalate ethanol solvate (2), 6,9-diamino-2-ethoxyacridinium phthalate isobutanol solvate (3), and 6,9-diamino-2-ethoxyacridinium phthalate tert-butanol solvate monohydrate (4) are described in this article. Single-crystal XRD measurements revealed that the compounds 1–4 crystallized in the triclinic P-1 space group, and the 6,9-diamino-2-ethoxyacridinium cations, phthalic acid anions and solvent molecules interact via strong N–H···O, O–H···O, C–H···O hydrogen bonds, and C–H···π and π–π interactions to form different types of basic structural motifs, such as: heterotetramer bis[···cation···anion···] in compound 1 and 2, heterohexamer bis[···cation···alcohol···anion···] in compound 3, and heterohexamer bis[···cation···water···anion···] in compound 4. Presence of solvents molecule(s) in the crystals causes different supramolecular synthons to be obtained and thus has an influence on the crystal packing of the compounds analyzed.

Pre-analytical and analytical confounders of serum calprotectin as a biomarker in rheumatoid arthritis

Background There is a need for additional biomarkers to assist in the diagnosis and prognosis of rheumatoid arthritis (RA). The aim of our study was to evaluate the (pre-analytical, analytical and clinical) performance of serum calprotectin as a marker of inflammation in RA. Methods The study population included 463 rheumatologic patients (including 111 RA patients and 352 controls) who for the first time consulted a rheumatologist, 20 healthy controls and 27 patients with an infectious disease. Calprotectin was measured (using four different assays) in serum or in serum and EDTA plasma (healthy controls and infectious disease group). For rheumatologic patients, results for C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibody (ACPA) were available. Results Results for blood calprotectin were assay- and matrix-dependent, with higher values found in serum than in plasma. Serum calprotectin was higher in RA patients than in rheumatologic diseased controls and in healthy controls. Serum calprotectin was lower in RA patients than in patients with an infectious disease. Serum calprotectin was associated with disease activity (DAS score). The area under the curve (AUC) to discriminate RA from controls was 0.756 for CRP, 0.714 for ESR and 0.726-0.783 for calprotectin. Conclusions Our data document that calprotectin measurement is assay- and matrix-dependent. Serum calprotectin is associated with disease activity. Additional (prospective) studies are warranted to further evaluate the prognostic and diagnostic value of blood calprotectin measurements.

Bioinformatic Mapping of Opine-Like Zincophore Biosynthesis in Bacteria

Bacteria must acquire essential nutrients, including zinc, from their environment. For bacterial pathogens, this necessitates overcoming the host metal-withholding response known as nutritional immunity. A novel type of zinc uptake mechanism that involves the bacterial production of a small zinc-scavenging molecule was recently described in the human pathogens Staphylococcus aureus, Pseudomonas aeruginosa, and Yersinia pestis, as well as the soil-associated bacterium Paenibacillus mucilaginosus. This suggests that zincophores may be important for zinc acquisition in diverse environments. In this study, we sought to identify other zincophore-producing bacteria using bioinformatics. We identified almost 250 unique zincophore-producing species, including human and animal pathogens, as well as isolates from soil, rhizosphere, plant, and marine habitats. Crucially, we observed diversity at the amino acid and gene organization levels, suggesting that many of these species are producing unique zincophores. Together, our findings highlight the importance of zincophores for a broad array of bacteria living in diverse environments.

Zinc is an essential nutrient in biological systems due to its structural or catalytic requirement in proteins involved in diverse cellular processes. To meet this cellular demand, microbes must acquire sufficient zinc from their environment. However, many environments have low zinc availability. One of the mechanisms used by bacteria to acquire zinc is through the production of small molecules known as zincophores. Similar to bacterial siderophores used for iron uptake, zincophores are synthesized by the bacterium and exported and then reimported as zincophore-zinc complexes. Thus far, only four zincophores have been described, including two from the human pathogens Staphylococcus aureus and Pseudomonas aeruginosa, in which they play a critical role in zinc acquisition during infection, and one in a soil bacterium. To determine what other microbes may produce zincophores, we used bioinformatic analyses to identify new zincophore biosynthetic gene clusters (BGCs) and predict the diversity of molecules synthesized. Genome neighborhood network analysis identified approximately 250 unique zincophore-producing species from actinobacteria, firmicutes, proteobacteria, and fusobacteria. This indicates that zincophores are produced by diverse bacteria that inhabit a broad range of ecological niches. Many of the BGCs likely produce characterized zincophores, based on similarity to the characterized systems. However, this analysis also identified numerous BGCs that, based on the colocalization of additional modifying enzymes and sequence divergence of the biosynthetic enzymes, are likely to produce unique zincophores. Collectively, these findings provide a comprehensive understanding of the zincophore biosynthetic landscape that will be invaluable for future research on these important small molecules.

IMPORTANCE Bacteria must acquire essential nutrients, including zinc, from their environment. For bacterial pathogens, this necessitates overcoming the host metal-withholding response known as nutritional immunity. A novel type of zinc uptake mechanism that involves the bacterial production of a small zinc-scavenging molecule was recently described in the human pathogens Staphylococcus aureus, Pseudomonas aeruginosa, and Yersinia pestis, as well as the soil-associated bacterium Paenibacillus mucilaginosus. This suggests that zincophores may be important for zinc acquisition in diverse environments. In this study, we sought to identify other zincophore-producing bacteria using bioinformatics. We identified almost 250 unique zincophore-producing species, including human and animal pathogens, as well as isolates from soil, rhizosphere, plant, and marine habitats. Crucially, we observed diversity at the amino acid and gene organization levels, suggesting that many of these species are producing unique zincophores. Together, our findings highlight the importance of zincophores for a broad array of bacteria living in diverse environments.

Faecal calprotectin in inflammatory bowel diseases: a review focused on meta-analyses and routine usage limitations

A growing body of evidence has been published about the usefulness of measuring calprotectin in faecal samples (FCAL) in inflammatory bowel disease (IBD) assessment, including diagnosis, monitoring of disease activity and relapse prediction. Several systematic reviews with meta-analyses compiling studies for each particular clinical setting have been carried out in recent years. Most of these were focused on the use of FCAL in IBD diagnosis and showed a relevant role for this marker in selecting patients with gastrointestinal symptoms who would not need a further examination by endoscopy. Although a lesser number of meta-analyses have been performed on the use of FCAL as a surrogate marker of disease activity, a close correlation between FCAL and endoscopic activity of IBD has been shown. With respect to the predictive capacity of FCAL for IBD relapse, a single meta-analysis published indicates that this role is more limited. Furthermore, FCAL thresholds vary considerably depending on the clinical setting and, what is more concerning, among different commercially available assays due to a lack of FCAL concentration interchangeability. Here, we summarise recent publications about the role and limitations of FCAL in IBD, with a special focus on meta-analyses, and give an overview of alternative faecal biomarkers.

Calcium Binding to the Innate Immune Protein Human Calprotectin Revealed by Integrated Mass Spectrometry

Although knowledge of the coordination chemistry and metal-withholding function of the innate immune protein human calprotectin (hCP) has broadened in recent years, understanding of its Ca²⁺-binding properties in solution remains incomplete. In particular, the molecular basis by which Ca²⁺ binding affects structure and enhances the functional properties of this remarkable transition-metal-sequestering protein has remained enigmatic. To achieve a molecular picture of how Ca²⁺ binding triggers hCP oligomerization, increases protease stability, and enhances antimicrobial activity, we implemented a new integrated mass spectrometry (MS)-based approach that can be readily generalized to study other protein-metal and protein-ligand interactions. Three MS-based methods (hydrogen/deuterium exchange MS kinetics; protein-ligand interactions in solution by MS, titration, and H/D exchange (PLIMSTEX); and native MS) provided a comprehensive analysis of Ca²⁺ binding and oligomerization to hCP without modifying the protein in any way. Integration of these methods allowed us to (i) observe the four regions of hCP that serve as Ca²⁺-binding sites, (ii) determine the binding stoichiometry to be four Ca²⁺ per CP heterodimer and eight Ca²⁺ per CP heterotetramer, (iii) establish the protein-to-Ca²⁺ molar ratio that causes the dimer-to-tetramer transition, and (iv) calculate the binding affinities associated with the four Ca²⁺-binding sites per heterodimer. These quantitative results support a model in which hCP exists in its heterodimeric form and is at most half-bound to Ca²⁺ in the cytoplasm of resting cells. With release into the extracellular space, hCP encounters elevated Ca²⁺ concentrations and binds more Ca²⁺ ions, forming a heterotetramer that is poised to compete with microbial pathogens for essential metal nutrients.

Metal Sequestration and Antimicrobial Activity of Human Calprotectin Are pH-Dependent

Human calprotectin (CP, S100A8/S100A9 oligomer) is an abundant innate immune protein that sequesters transition metal ions in the extracellular space to limit nutrient availability and the growth of invading microbial pathogens. Our current understanding of the metal-sequestering ability of CP is based on biochemical and functional studies performed at neutral or near-neutral pH. Nevertheless, CP can be present throughout the human body and is expressed at infection and inflammation sites that tend to be acidic. Here, we evaluate the metal binding and antimicrobial properties of CP in the pH range of 5.0-7.0. We show that Ca(II)-induced tetramerization, an important process for the extracellular functions of CP, is perturbed by acidic conditions. Moreover, a low pH impairs the antimicrobial activity of CP against some bacterial pathogens, including Staphylococcus aureus and Salmonella enterica serovar Typhimurium. At a mildly acidic pH, CP loses the ability to deplete Mn from microbial growth medium, indicating that Mn(II) sequestration is attenuated under acidic conditions. Evaluation of the Mn(II) binding properties of CP at pH 5.0-7.0 indicates that mildly acidic conditions decrease the Mn(II) binding affinity of the His₆ site. Lastly, CP is less effective at preventing capture of Mn(II) by the bacterial solute-binding proteins MntC and PsaA at low pH. These results indicate that acidic conditions compromise the ability of CP to sequester Mn(II) and starve microbial pathogens of this nutrient. This work highlights the importance of considering the local pH of biological sites when describing the interplay between CP and microbes in host-pathogen interactions.

Epigenetic Regulation of S100A9 and S100A12 Expression in Monocyte-Macrophage System in Hyperglycemic Conditions

The number of diabetic patients in Europe and world-wide is growing. Diabetes confers a 2-fold higher risk for vascular disease. Lack of insulin production (Type 1 diabetes, T1D) or lack of insulin responsiveness (Type 2 diabetes, T2D) causes systemic metabolic changes such as hyperglycemia (HG) which contribute to the pathology of diabetes. Monocytes and macrophages are key innate immune cells that control inflammatory reactions associated with diabetic vascular complications. Inflammatory programming of macrophages is regulated and maintained by epigenetic mechanisms, in particular histone modifications. The aim of our study was to identify the epigenetic mechanisms involved in the hyperglycemia-mediated macrophage activation. Using Affymetrix microarray profiling and RT-qPCR we identified that hyperglycemia increased the expression of S100A9 and S100A12 in primary human macrophages. Expression of S100A12 was sustained after glucose levels were normalized. Glucose augmented the response of macrophages to Toll-like receptor (TLR)-ligands Palmatic acid (PA) and Lipopolysaccharide (LPS) i.e., pro-inflammatory stimulation. The abundance of activating histone Histone 3 Lysine 4 methylation marks (H3K4me1, H3K4me3) and general acetylation on histone 3 (AceH3) with the promoters of these genes was analyzed by chromatin immunoprecipitation. Hyperglycemia increased acetylation of histones bound to the promoters of S100A9 and S100A12 in M1 macrophages. In contrast, hyperglycemia caused a reduction in total H3 which correlated with the increased expression of both S100 genes. The inhibition of histone methyltransferases SET domain-containing protein (SET)7/9 and SET and MYND domain-containing protein (SMYD)3 showed that these specifically regulated S100A12 expression. We conclude that hyperglycemia upregulates expression of S100A9, S100A12 via epigenetic regulation and induces an activating histone code on the respective gene promoters in M1 macrophages. Mechanistically, this regulation relies on action of histone methyltransferases SMYD3 and SET7/9. The results define an important role for epigenetic regulation in macrophage mediated inflammation in diabetic conditions.

Disruption of Phosphate Homeostasis Sensitizes Staphylococcus aureus to Nutritional Immunity

To control infection, mammals actively withhold essential nutrients, including the transition metal manganese, by a process termed nutritional immunity. A critical component of this host response is the manganese-chelating protein calprotectin. While many bacterial mechanisms for overcoming nutritional immunity have been identified, the intersection between metal starvation and other essential inorganic nutrients has not been investigated. Here, we report that overexpression of an operon encoding a highly conserved inorganic phosphate importer, PstSCAB, increases the sensitivity of Staphylococcus aureus to calprotectin-mediated manganese sequestration. Further analysis revealed that overexpression of pstSCAB does not disrupt manganese acquisition or result in overaccumulation of phosphate by S. aureus However, it does reduce the ability of S. aureus to grow in phosphate-replete defined medium. Overexpression of pstSCAB does not aberrantly activate the phosphate-responsive two-component system PhoPR, nor was this two-component system required for sensitivity to manganese starvation. In a mouse model of systemic staphylococcal disease, a pstSCAB-overexpressing strain is significantly attenuated compared to wild-type S. aureus This defect is partially reversed in a calprotectin-deficient mouse, in which manganese is more readily available. Given that expression of pstSCAB is regulated by PhoPR, these findings suggest that overactivation of PhoPR would diminish the ability of S. aureus to resist nutritional immunity and cause infection. As PhoPR is also necessary for bacterial virulence, these findings imply that phosphate homeostasis represents a critical regulatory node whose activity must be precisely controlled in order for S. aureus and other pathogens to cause infection.

The predictive role of serum calprotectin on mortality in hemodialysis patients with high phosphoremia

Background

The inflammatory mediator calprotectin (CPT, myeloid-related protein 8/14) is known as an endogenous ligand contributing to pathophysiology in inflammatory diseases. Serum CPT reportedly became a potential biomarker in these conditions, though there is no report predicting the prognosis in hemodialysis patients. The aim of this study is to investigate the predictive role of serum CPT on mortality in hemodialysis patients.

Methods

We conducted a multicenter, observational cohort study of 388 Japanese subjects undergoing hemodialysis. Serum CPT were measured using an ELISA. The potential associations between serum CPT and clinical variables were cross-sectionally examined. Multivariate Cox regression was used to estimate the association between serum CPT, high-sensitivity C reactive protein (hs-CRP), white blood cell (WBC) count and mortality. Median follow-up was 6.6 years.

Results

The median CPT level was 6108 ng/ml (median in healthy subjects, 2800) at baseline. Serum CPT positively correlated with WBC count (ρ = 0.54, P < 0.001) and hs-CRP values (ρ = 0.35, P < 0.001). In multivariate analysis, hs-CRP was an independent predictor of all-cause mortality after adjusting confounding factors (middle vs. low: hazard ratio [HR] 2.09, 95% confidence interval [CI] 1.23–3.66; high vs. low: 2.47, 1.40–4.47). In the analysis by stratum of phosphate levels, elevated CPT levels were significantly associated with all-cause mortality in the highest tertile (18.1; 3.15–345.9) among the high-phosphate group, but not among the low-phosphate group.

Conclusions

Serum CPT would become a potential predictive marker on mortality in hemodialysis patients with high-phosphate levels.

Effects of unsaturated fatty acids (Arachidonic/Oleic Acids) on stability and structural properties of Calprotectin using molecular docking and molecular dynamics simulation approach

Calprotectin is a heterodimeric protein complex with two subunits called S100A8/A9. The protein has an essential role in inflammation process and various human diseases. It has the ability to bind to unsaturated fatty acids including Arachidonic acid, Oleic acid and etc., which could be considered as a major carrier for fatty acids. In this study we aimed to appraise the thermodynamics and structural changes of Calprotectin in presence of Arachidonic acid/Oleic acid) using docking and molecular dynami simulation method. To create the best conformation of Calprotectin-Oleic acid/Arachidonic acid complexes, the docking process was performed. The complexes with the best binding energy were selected as the models for molecular dynamics simulation process. Furthermore, the structural and thermodynamics properties of the complexes were evaluated too. The Root Mean Square Deviation and Root Mean Square Fluctuation results showed that the binding of Arachidonic acid/Oleic acid to Calprotectin can cause the protein structural changes which was confirmed by Define Secondary Structure of Proteins results. Accordingly, the binding free energy results verified that binding of Oleic acid to Calprotectin leads to instability of S100A8/A9 subunits in the protein. Moreover, the electrostatic energy contribution of the complexes (Calprotectin-Oleic acid/Arachidonic acid) was remarkably higher than van der Waals energy. Thus, the outcome of this study confirm that Oleic acid has a stronger interaction with Calprotectin in comparison with Arachidonic acid. Our findings indicated that binding of unsaturated fatty acids to Calprotectin leads to structural changes of the S100A8/A9 subunits which could be beneficial to play a biological role in inflammation process.

Calprotectin (S100A8/S100A9)-induced cytotoxicity and apoptosis in human gastric cancer AGS cells: Alteration in expression levels of Bax, Bcl-2, and ERK2

Calprotectin is a heterodimeric EF-hand Ca²⁺ binding protein that is typically released by infiltrating polymorphonuclear leukocytes and macrophages. This protein is a key player linking inflammation and cancer. Due to the increased levels of calprotectin in different inflammatory diseases and cancer, it is considered as a marker for diagnostic purposes. In this study, we evaluated the mechanism of cell viability and apoptotic-inducing effects of recombinant human calprotectin (rhS100A8/S100A9) on the gastric adenocarcinoma (AGS), the most common type of gastric cancer cell line. AGS cells were exposed to the different concentrations (5-100 μg/ml) of calprotectin for 24, 48, and 72 h, and cell viability was assessed through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Apoptotic-inducing effects of calprotectin were evaluated by sub-G1 cell cycle assay and Annexin V/propidium iodide double staining. Furthermore, real-time polymerase chain reaction and Western blot analysis were performed to evaluate the mechanism of action of calprotectin. Our findings indicated that calprotectin inhibits growth and viability of AGS cells in a time- and dose-dependent manner. The half-maximal inhibitory concentration values were measured as 85.77, 79.14, and 65.39 μg/ml for 24, 48, and 72 h, respectively. Additionally, we found that calprotectin downregulated the expression of antiapoptotic protein Bcl-2 and upregulated proapoptotic protein Bax in a time- and concentration-dependent fashion. Calprotectin also slightly upregulated the expression of extracellular signal-regulated protein kinase 2 (ERK2), while it significantly decreased the levels of phospho-ERK in a time-dependent manner. Overall, these findings indicated that calprotectin has cytotoxicity and apoptosis-inducing effects on AGS cell lines in high concentration by modulating Bax/Bcl-2 expression ratio accompanied by inhibition of ERK activation.

Avian MRP126 Restricts Microbial Growth through Ca(II)-Dependent Zn(II) Sequestration

The calgranulins form a class of S100 proteins in higher vertebrates that innate-immune cells release in abundance at infection sites. These proteins function by binding transition metal ions to prevent microbial pathogens from obtaining those essential nutrients. Mammals express three distinct members of this family: S100A8 (calgranulin A), S100A9 (calgranulin B, which heterooligomerizes with S100A8 to form calprotectin), and S100A12 (calgranulin C), that exhibit Ca(II)-dependent transition metal binding properties. Human calprotectin effectively sequesters Mn(II), Fe(II), Ni(II), and Zn(II), whereas human S100A12 selectively sequesters Zn(II) over these other metal ions. Birds and reptiles express a single calgranulin homologue named MRP126, which we reasoned could have properties more similar to those of either calprotectin or S100A12. Here we present the purification and biophysical characterization of recombinant chicken MRP126 and, to the best of our knowledge, provide the first assessment of the metal binding and antimicrobial properties of an avian MRP126. We show that MRP126 is a homodimer that selectively sequesters Zn(II) and restricts the growth of certain microbes. MRP126 binds Zn(II) at two canonical His₃Asp sites. The presence of excess Ca(II) increases the affinity of the His₃Asp sites from the low-nanomolar to the low-picomolar range, thereby enhancing antimicrobial activity. Chicken MRP126 also binds additional Zn(II) equivalents with low-nanomolar affinity at two nonconserved dicysteine sites and with high-nanomolar affinity using a histidine-rich C-terminal tail that is a hallmark of this clade of calgranulins. Our results with chicken MRP126 suggest that Ca(II)-dependent Zn(II) sequestration was a role of the last common ancestor of calgranulin proteins, with mammalian calprotectin subsequently evolving a broader metal binding repertoire.

Critical role and its underlying molecular events of the plasminogen receptor, S100A10 in malignant tumor and non-tumor diseases

S100A10 is a small molecular weight protein expressed in the cytoplasm of many cells and one of the members of the S100 protein family that binds calcium and forms the largest subgroup of EF-hand proteins. The regulatory processes of S100A10 are complicated. S100A10 participates in the regulation of a variety of tumor and non-tumor diseases through cascade reactions with multitudinous signaling molecules. In malignant tumors, such as acute promyelocytic leukemia (APL) and lung cancer, S100A10 is likely involved in their progression, including invasion and metastasis through the regulation of plasmin production and subsequent plasmin-dependent stimulation of other proteases, such as matrix metalloproteinase (MMP)-2 and -9. Both the plasmin and MMPs are capable of inducing degradation of the extracellular matrix (ECM) and basement membrane, which is a critical step for tumor progression. In non-tumor diseases, the distribution of S100A10 in the brain and its interaction with 5-hydroxytryptamine 1B (5-HT1B) receptor, an important mediator in the central nervous system that maintains a dynamic balance of the neurotransmitters, correlates with depression-like behavior. S100A10 also participates in inflammatory responses through the regulation of peripheral macrophage migration to the inflammatory sites, which depends on the generation of plasmin and other proteinases at the surface of macrophages. Considerable attention should be paid to understand the significant role of S100A10 in the modulation of malignant tumor and non-tumor diseases.

Nutrient Zinc at the Host-Pathogen Interface

Zinc is an essential cofactor required for life and, as such, mechanisms exist for its homeostatic maintenance in biological systems. Despite the evolutionary distance between vertebrates and microbial life, there are parallel mechanisms to balance the essentiality of zinc with its inherent toxicity. Vertebrates regulate zinc homeostasis through a complex network of metal transporters and buffering systems that respond to changes in nutritional zinc availability or inflammation. Fine-tuning of this network becomes crucial during infections, where host nutritional immunity attempts to limit zinc availability to pathogens. However, accumulating evidence demonstrates that pathogens have evolved mechanisms to subvert host-mediated zinc withholding, and these metal homeostasis systems are important for survival within the host. We discuss here the mechanisms of vertebrate and bacterial zinc homeostasis and mobilization, as well as recent developments in our understanding of microbial zinc acquisition.

In silico assessment of human Calprotectin subunits (S100A8/A9) in presence of sodium and calcium ions using Molecular Dynamics simulation approach

Calprotectin is a heterodimeric protein complex which consists of two subunits including S100A8 and S100A9. This protein has a major role in different inflammatory disease and various types of cancers. In current study we aimed to evaluate the structural and thermodynamic changes of the subunits and the complex in presence of sodium and calcium ions using molecular dynamics (MD) simulation. Therefore, the residue interaction network (RIN) was visualized in Cytoscape program. In next step, to measure the binding free energy, the potential of mean force (PMF) method was performed. Finally, the molecular mechanics Poisson-Boltzmann surface area (MMPBSA) method was applied as an effective tool to calculate the molecular model affinities. The MD simulation results of the subunits represented their structural changes in presence of Ca2+. Moreover, the RIN and Hydrogen bond analysis demonstrated that cluster interactions between Calprotectin subunits in presence of Ca2+ were greater in comparison with Na+. Our findings indicated that the binding free energy of the subunits in presence of Ca2+ was significantly greater than Na+. The results revealed that Ca2+ has the ability to induce structural changes in subunits in comparison with Na+ which lead to create stronger interactions between. Hence, studying the physical characteristics of the human proteins could be considered as a powerful tool in theranostics and drug design purposes.

Enhanced myelopoiesis and aggravated arthritis in S100a8-deficient mice

Expressed strongly by myeloid cells, damage-associated molecular pattern (DAMP) proteins S100A8 and S100A9 are found in the serum of patients with infectious and autoimmune diseases. Compared to S100A9, the role of S100A8 is controversial. We investigated its biological activity in collagen-induced arthritis using the first known viable and fertile S100a8-deficient (S100a8^-/-) mouse. Although comparable to the wild type (WT) in terms of lymphocyte distribution in blood and in the primary and secondary lymphoid organs, S100a8^-/- mice had increased numbers of neutrophils, monocytes and dendritic cells in the blood and bone marrow, and these all expressed myeloid markers such as CD11b, Ly6G and CD86 more strongly. Granulocyte-macrophage common precursors were increased in S100a8^-/- bone marrow and yielded greater numbers of macrophages and dendritic cells in culture. The animals also developed more severe arthritic disease leading to aggravated osteoclast activity and bone destruction. These findings were correlated with increased inflammatory cell infiltration and cytokine secretion in the paws. This study suggests that S100A8 is an anti-inflammatory DAMP that regulates myeloid cell differentiation, thereby mitigating the development of experimental arthritis.

Exploring Iron Withholding by the Innate Immune Protein Human Calprotectin

Calprotectin (CP) is a versatile player in the metal-withholding innate immune response, a process termed "nutritional immunity." CP is a heterooligomer of the polypeptides S100A8 and S100A9 and houses two transition-metal-binding sites at its S100A8/S100A9 heterodimer interface. During infection, CP is released from host cells and sequesters "bioavailable" transition metal ions in the extracellular space, thereby preventing microbial acquisition of these essential nutrients. For many years, the role of CP in nutritional immunity was interpreted in the contexts of Mn(II) and Zn(II) limitation, but recent work has broadened our understanding of its contributions to this process. We uncovered that CP provides a form of nutritional immunity that has previously received little attention: the battle between host and microbe for ferrous iron (Fe(II)). In this Account, we present our current understanding of Fe(II) coordination by CP and its role in Fe(II) withholding as well as considerations for future discovery. Nutritional immunity was first described in the context of host-microbe competition for ferric iron (Fe(III)). The battle for Fe(II) has received comparably little attention because the abundance of Fe(II) at infection sites and the importance of Fe(II) acquisition for microbial pathogenesis were recognized only recently. Several years ago, we discovered that human CP sequesters Fe(II) at its His6 site with subpicomolar affinity and thus hypothesized that it provides a means for Fe(II) limitation by the host during microbial infection. Fe(II) coordination by CP is unprecedented in biology because of its novel hexahistidine coordination sphere and its high-affinity binding, which surpasses that of other known Fe(II)-binding proteins. CP is also capable of shifting the Fe redox equilibrium by stabilizing Fe(II) in aerobic solution and can thereby sequester Fe in both reducing and nonreducing environments. These coordination chemistry studies allowed us to hypothesize that CP provides a means for Fe(II) limitation by the host during microbial infection. While investigating this putative Fe(II)-sequestering function, we discovered that CP withholds Fe from diverse bacterial pathogens. Recent studies by our lab and others of the bacterial pathogens Pseudomonas aeruginosa and Acinetobacter baumannii have shown that, by preventing sufficient Fe acquisition, CP induces Fe starvation responses in these organisms. As a result, CP affects bacterial virulence and metabolism. We also elucidated a complex interplay between CP and secondary metabolites produced by P. aeruginosa during the competition for Fe. Our work provides a foundation for understanding how CP affects Fe homeostasis during microbial infection. We believe that understanding how bacterial physiology is altered when challenged with Fe(II) withholding by CP will likely reveal crucial determinants of bacterial survival within the host.

Disruption of Glycolysis by Nutritional Immunity Activates a Two-Component System That Coordinates a Metabolic and Antihost Response by Staphylococcus aureus

During infection, bacteria use two-component signal transduction systems to sense and adapt to the dynamic host environment. Despite critically contributing to infection, the activating signals of most of these regulators remain unknown. This also applies to the Staphylococcus aureus ArlRS two-component system, which contributes to virulence by coordinating the production of toxins, adhesins, and a metabolic response that enables the bacterium to overcome host-imposed manganese starvation. Restricting the availability of essential transition metals, a strategy known as nutritional immunity, constitutes a critical defense against infection. In this work, expression analysis revealed that manganese starvation imposed by the immune effector calprotectin or by the absence of glycolytic substrates activates ArlRS. Manganese starvation imposed by calprotectin also activated the ArlRS system even when glycolytic substrates were present. A combination of metabolomics, mutational analysis, and metabolic feeding experiments revealed that ArlRS is activated by alterations in metabolic flux occurring in the latter half of the glycolytic pathway. Moreover, calprotectin was found to induce expression of staphylococcal leukocidins in an ArlRS-dependent manner. These studies indicated that ArlRS is a metabolic sensor that allows S. aureus to integrate multiple environmental stresses that alter glycolytic flux to coordinate an antihost response and to adapt to manganese starvation. They also established that the latter half of glycolysis represents a checkpoint to monitor metabolic state in S. aureus Altogether, these findings contribute to understanding how invading pathogens, such as S. aureus, adapt to the host during infection and suggest the existence of similar mechanisms in other bacterial species.IMPORTANCE Two-component regulatory systems enable bacteria to adapt to changes in their environment during infection by altering gene expression and coordinating antihost responses. Despite the critical role of two-component systems in bacterial survival and pathogenesis, the activating signals for most of these regulators remain unidentified. This is exemplified by ArlRS, a Staphylococcus aureus global regulator that contributes to virulence and to resisting host-mediated restriction of essential nutrients, such as manganese. In this report, we demonstrate that manganese starvation and the absence of glycolytic substrates activate ArlRS. Further investigations revealed that ArlRS is activated when the latter half of glycolysis is disrupted, suggesting that S. aureus monitors flux through the second half of this pathway. Host-imposed manganese starvation also induced the expression of pore-forming toxins in an ArlRS-dependent manner. Cumulatively, this work reveals that ArlRS acts as a sensor that links nutritional status, cellular metabolism, and virulence regulation.

Metal-independent variants of phosphoglycerate mutase promote resistance to nutritional immunity and retention of glycolysis during infection

The ability of Staphylococcus aureus and other pathogens to consume glucose is critical during infection. However, glucose consumption increases the cellular demand for manganese sensitizing S. aureus to host-imposed manganese starvation. The current investigations were undertaken to elucidate how S. aureus copes with the need to consume glucose when metal-limited by the host. A critical component of host defense is production of the manganese binding protein calprotectin. S. aureus has two variants of phosphoglycerate mutase, one of which is manganese-dependent, GpmI, and another that is manganese-independent, GpmA. Leveraging the ability to impose metal starvation in culture utilizing calprotectin revealed that the loss of GpmA, but not GpmI, sensitized S. aureus to manganese starvation. Metabolite feeding experiments revealed that the growth defect of GpmA when manganese-starved was due to a defect in glycolysis and not gluconeogenesis. Loss of GpmA reduces the ability of S. aureus to cause invasive disease in wild type mice. However, GpmA was dispensable in calprotectin-deficient mice, which have defects in manganese sequestration, indicating that this isozyme contributes to the ability of S. aureus to overcome manganese limitation during infection. Cumulatively, these observations suggest that expressing a metal-independent variant enables S. aureus to consume glucose while mitigating the negative impact that glycolysis has on the cellular demand for manganese. S. aureus is not the only bacterium that expresses manganese-dependent and -independent variants of phosphoglycerate mutase. Similar results were also observed in culture with Salmonella enterica serovar Typhimurium mutants lacking the metal-independent isozyme. These similar observations in both Gram-positive and Gram-negative pathogens suggest that expression of metal-independent glycolytic isozymes is a common strategy employed by bacteria to survive in metal-limited environments, such as the host.

Pathogens, such as Staphylococcus aureus and Salmonella species, must be able to consume glucose in order to cause infection. However, glycolysis can increase the need for manganese and sensitize invaders to the manganese-withholding defense of the host, known as nutritional immunity. How pathogens manage these conflicting pressures is currently unknown. The current investigations revealed that a second metal-independent variant of phosphoglycerate mutase possessed by both S. aureus and Salmonella enables them to grow and consume glycolytic substrates in the presence of the manganese-binding immune effector calprotectin. Infection experiments revealed that the manganese-independent isozyme critically contributes to the ability of S. aureus to overcome manganese starvation during infection. Together, these results suggest that using metal-independent isozymes to enable the consumption of sugars within the host or other metal-limited environments is a common strategy employed by diverse bacteria.

Transcriptomics of Human Arteriovenous Fistula Failure: Genes Associated With Nonmaturation

RATIONALE & OBJECTIVE

Improving arteriovenous fistula (AVF) outcomes requires better understanding of the biology underlying maturation or failure. Our current knowledge of maturation relies on extrapolation from other vascular pathologies, which does not incorporate unique aspects of AVF remodeling. This study compares the RNA expression of pre-access (native) veins and AVFs with distinct maturation outcomes.

STUDY DESIGN

Case-control study.

SETTING & PARTICIPANTS

64 patients undergoing 2-stage AVF surgeries at a single center. 19 native veins and 19 AVF samples were analyzed using RNA sequencing (RNA-seq). 58 native veins were studied using real-time polymerase chain reaction; 45, using immunohistochemistry; and 19, using Western blot analysis.

PREDICTOR

RNA expression in native veins and AVFs.

OUTCOME

Anatomic nonmaturation, defined as an AVF that never achieved an internal diameter ≥ 6mm.

ANALYTICAL APPROACH

Pre-access native veins and AVF samples were obtained from patients undergoing 2-stage AVF creation. Veins that subsequently matured or failed after access creation were analyzed using RNA-seq to search for genes associated with maturation failure. Genes associated with nonmaturation were confirmed using real-time polymerase chain reaction, immunohistochemistry, and Western blot analysis. In addition, the association between pre-access gene expression and postoperative morphology was evaluated. RNA-seq was also performed on AVFs to search for transcriptional differences between AVFs that matured and those that failed at the time of transposition.

RESULTS

Pro-inflammatory genes (CSF3R, FPR1, S100A8, S100A9, and VNN2) were upregulated in pre-access veins that failed (false discovery rate < 0.05), and their expression colocalized to smooth muscle cells. Expression of S100A8 and S100A9 correlated with postoperative intimal hyperplasia and the product of medial fibrosis and intimal hyperplasia (r=0.32-0.38; P < 0.05). AVFs that matured or failed were transcriptionally similar at the time of transposition.

LIMITATIONS

Small sample size, analysis of only upper-arm veins and transposed fistulas.

CONCLUSIONS

Increased expression of proinflammatory genes in pre-access veins appears to be associated with greater risk for AVF nonmaturation.

Murine Calprotectin Coordinates Mn(II) at a Hexahistidine Site with Ca(II)-Dependent Affinity

Manganese is an essential metal ion that bacterial pathogens need to acquire from the vertebrate host during infection. In the mammalian nutritional immunity strategy to combat bacterial infection, the host restricts bacterial access to Mn(II) by sequestering this metal nutrient using the protein calprotectin (CP). The role of murine calprotectin (mCP) in Mn(II) sequestration has been demonstrated in vivo, but the molecular basis of this function has not been evaluated. Herein, biochemical assays and electron paramagnetic resonance (EPR) spectroscopy are employed to characterize the Mn(II) binding properties of mCP. We report that mCP has one high-affinity Mn(II) binding site. This site is a His₆ site composed of His17 and His27 of mS100A8 and His92, His97, His105, and His107 of mS100A9. Similar to the human ortholog (hCP), Ca(II) binding to the EF-hand domains of mCP enhances the Mn(II) affinity of the protein; however, this effect requires ≈10-fold more Ca(II) than was previously observed for hCP. Mn(II) coordination to the His₆ site also promotes self-association of two mCP heterodimers to form a heterotetramer. Low-temperature X-band EPR spectroscopy revealed a nearly octahedral Mn(II) coordination sphere for the Mn(II)-His₆ site characterized by the zero-field splitting parameters D = 525 MHz and E/D = 0.3. Further electron-nuclear double resonance studies with globally ¹⁵N-labeled mCP provided hyperfine couplings from the coordinating ε-nitrogen atoms of the His ligands (a_iso = 4.3 MHz) as well as the distal δ-nitrogen atoms (a_iso = 0.25 MHz). Mn(II) competition assays between mCP and two bacterial Mn(II) solute-binding proteins, staphylococcal MntC and streptococcal PsaA, showed that mCP outcompetes both proteins for Mn(II) under conditions of excess Ca(II). In total, this work provides the first coordination chemistry study of mCP and reveals striking similarities in the Mn(II) coordination sphere as well as notable differences in the Ca(II) sensitivity and oligomerization behavior between hCP and mCP.

Ca(II) and Zn(II) Cooperate To Modulate the Structure and Self-Assembly of S100A12

S100A12 is a member of the Ca²⁺ binding S100 family of proteins that functions within the human innate immune system. Zinc sequestration by S100A12 confers antimicrobial activity when the protein is secreted by neutrophils. Here, we demonstrate that Ca²⁺ binding to S100A12's EF-hand motifs and Zn²⁺ binding to its dimeric interface cooperate to induce reversible self-assembly of the protein. Solution and magic angle spinning nuclear magnetic resonance spectroscopy on apo-, Ca²⁺-, Zn²⁺-, and Ca²⁺,Zn²⁺-S100A12 shows that significant metal binding-induced chemical shift perturbations, indicative of conformational changes, occur throughout the polypeptide chain. These perturbations do not originate from changes in the secondary structure of the protein, which remains largely preserved. While the overall structure of S100A12 is dominated by Ca²⁺ binding, Zn²⁺ binding to Ca²⁺-S100A12 introduces additional structural changes to helix II and the hinge domain (residues 38-53). The hinge domain of S100A12 is involved in the molecular interactions that promote chemotaxis for human monocyte, acute inflammatory responses and generates edema. In Ca²⁺-S100A12, helix II and the hinge domain participate in binding with the C-type immunoglobulin domain of the receptor for advanced glycation products (RAGE). We discuss how the additional conformational changes introduced to these domains upon Zn²⁺ binding may also impact the interaction of S100A12 and target proteins such as RAGE.

A subset of calcium-binding S100 proteins show preferential heterodimerization

The assembly of proteins into dimers and oligomers is a necessary step for the proper function of transcription factors, muscle proteins, and proteases. In uncontrolled states, oligomerization can also contribute to illnesses such as Alzheimer's disease. The S100 protein family is a group of dimeric proteins that have important roles in enzyme regulation, cell membrane repair, and cell growth. Most S100 proteins have been examined in their homodimeric state, yet some of these important proteins are found in similar tissues implying that heterodimeric molecules can also be formed from the combination of two different S100 members. In this work, we have established co-expression methods in order to identify and quantify the distribution of homo- and heterodimers for four specific pairs of S100 proteins in their calcium-free states. The split GFP trap methodology was used in combination with other GFP variants to simultaneously quantify homo- and heterodimeric S100 proteins in vitro and in living cells. For the specific S100 proteins examined, NMR, mass spectrometry, and GFP trap experiments consistently show that S100A1:S100B, S100A1:S100P, and S100A11:S100B heterodimers are the predominant species formed compared to their corresponding homodimers. We expect the tools developed here will help establish the roles of S100 heterodimeric proteins and identify how heterodimerization might alter the specificity for S100 protein action in cells.

Measuring calprotectin in plasma and blood with a fully automated turbidimetric assay

Calprotectin in plasma and blood might prove to be a useful biomarker of inflammation and infection; however, automated methods for analysing the concentration of calprotectin in those materials are lacking. We have validated a fully automated turbidimetric method and present health-related reference limits. Calprotectin was measured by Siemens Advia XPT with the Bühlmann fCAL® turbo test (Bühlmann Laboratories AG, Schönenbuch, Switzerland), a particle enhanced turbidimetric immunoassay for quantification of calprotectin in fecal extracts. Plasma and serum samples were analysed directly, while whole blood was first extracted with M-PER® Mammalian Protein Extraction Reagent (ThermoFisher) and diluted with B-CAL-EX (Bühlmann). We studied analytical imprecision, estimated health-related reference limits and examined the correlation between neutrophil-calprotectin (blood-calprotectin adjusted for plasma-calprotectin) and the neutrophil count. The intermediate ('day-to-day') coefficient of variation was 3.5 and 1.0% for heparin-plasma-calprotectin at 0.52 mg/L and 3.53 mg/L, respectively, and 4.9% for heparin-blood-calprotectin at 50.2 mg/L. Health-related reference limits were 0.470-3.02 mg/L for calprotectin in heparin-plasma, 50.8-182 mg/L for calprotectin in heparin-blood, 0.534-2.41% for the ratio between them and 24.7-33.3 pg for the mean amount of calprotectin per neutrophil. Compared to heparin-plasma, calprotectin concentrations were significantly lower in EDTA-plasma and higher in serum (p < .05). Correlation between neutrophil-calprotectin and the neutrophil count was excellent. We have shown that the Bühlmann fCAL® turbo test can be used to measure calprotectin in plasma and blood.

Systemic calprotectin and chronic inflammatory rheumatic diseases

Calprotectin is a calcium binding protein produced by neutrophils and monocytes locally at the site of inflammation in order to trigger the innate immunity receptors. This unique characteristic makes it a good proxy for evaluation of local inflammation in chronic inflammatory rheumatic diseases. Complete data suggest, in inflammatory rheumatic diseases, a relevant role of calprotectin in the inflammatory process. The interest of serum or plasma calprotectin dosage has been studied intensively, in the current years, especially in rheumatoid arthritis, spondyloarthritis, juvenile idiopathic arthritis and ANCA associated vasculitis. Calprotectin seems to be a great candidate as biomarker to assess and monitor disease activity, to predict structural progression or response to the treatment. Calprotectin showed its ability to predict radiological progression in rheumatoid arthritis and ankylosing spondylitis. Serum calprotectin can predict the risk of relapse in ANCA associated vasculitis and the risk of inflammatory bowel disease in spondyloarthritis. Nevertheless, studies report controversial result requiring replication in other large cohort. The lack of assay standardization between studies is a problem to replicate and compare studies. In this review, we discuss on the interest of systemic calprotectin in chronic inflammatory rheumatic disease as a diagnostic, activity or prognostic biomarker.

The human innate immune protein calprotectin induces iron starvation responses in Pseudomonas aeruginosa

Most microbial pathogens have a metabolic iron requirement, necessitating the acquisition of this nutrient in the host. In response to pathogen invasion, the human host limits iron availability. Although canonical examples of nutritional immunity are host strategies that limit pathogen access to Fe(III), little is known about how the host restricts access to another biologically relevant oxidation state of this metal, Fe(II). This redox species is prevalent at certain infection sites and is utilized by bacteria during chronic infection, suggesting that Fe(II) withholding by the host may be an effective but unrecognized form of nutritional immunity. Here, we report that human calprotectin (CP; S100A8/S100A9 or MRP8/MRP14 heterooligomer) inhibits iron uptake and induces an iron starvation response in Pseudomonas aeruginosa cells by sequestering Fe(II) at its unusual His₆ site. Moreover, under aerobic conditions in which the Fe(III) oxidation state is favored, Fe(II) withholding by CP was enabled by (i) its ability to stabilize this redox state in solution and (ii) the production and secretion of redox-active, P. aeruginosa-produced phenazines, which reduce Fe(III) to Fe(II). Analyses of the interplay between P. aeruginosa secondary metabolites and CP indicated that Fe(II) withholding alters P. aeruginosa physiology and expression of virulence traits. Lastly, examination of the effect of CP on cell-associated metal levels in diverse human pathogens revealed that CP inhibits iron uptake by several bacterial species under aerobic conditions. This work implicates CP-mediated Fe(II) sequestration as a component of nutritional immunity in both aerobic and anaerobic milieus during P. aeruginosa infection.

Synergy between Nutritional Immunity and Independent Host Defenses Contributes to the Importance of the MntABC Manganese Transporter during Staphylococcus aureus Infection

During infection, the host utilizes a diverse array of processes to combat invaders, including the restriction of availability of essential nutrients such as manganese. Similarly to many other pathogens, Staphylococcus aureus possesses two manganese importers, MntH and MntABC. Several infection models have revealed a critical role for MntABC during staphylococcal infection. However, culture-based studies have suggested parity between the two transporters when cells are resisting manganese starvation imposed by the manganese binding immune effector calprotectin. In this investigation, initial elemental analysis revealed that MntABC is the primary transporter responsible for obtaining manganese in culture in the presence of calprotectin. MntABC was also necessary to maintain wild-type levels of manganese-dependent superoxide dismutase activity in the presence of calprotectin. Building on this framework, we investigated if MntABC enabled S. aureus to resist the synergistic actions of nutritional immunity and other host defenses. This analysis revealed that MntABC critically contributes to staphylococcal growth when S. aureus is subjected to manganese limitations and exposed to oxidative stress. This transporter was also important for growth in manganese-limited environments when S. aureus was forced to consume glucose as an energy source, which occurs when it encounters nitric oxide. MntABC also expanded the pH range conducive for S. aureus growth under conditions of manganese scarcity. Collectively, the data presented in this work provide a robust molecular basis for the crucial role of MntABC in staphylococcal virulence. Further, this work highlights the importance of synergy between host defenses and the necessity of evaluating the contribution of virulence factors to pathogenesis in the presence of multiple stressors.

Reviewing the Crystal Structure of S100Z and Other Members of the S100 Family: Implications in Calcium-Regulated Quaternary Structure

This paper takes the cue from the previously solved crystal structure of human apo-S100Z and compares it with that of the calcium-bound S100Z from zebrafish in order to stress, for this particular S100, the significant role of the presence of calcium in promoting supramolecular assemblies with likely biological meaning. This consideration is then expanded through a wider review on analogous situations concerning all other S100s for which there is crystallographic o biochemical evidence of how the presence of calcium promotes the formation of quaternary complexes.The paper also deals with some considerations on the quality of the crystals obtained for the solved members of this family and on the need for experimental phasing for solving some of the structures where the good general sequence homology among the members of the family would have suggested molecular replacement (MR) as the easiest way to solve them.These considerations, along with the PCA analysis carried out on all the known S100s, further demonstrate that calcium plays a fundamental role in triggering quaternary structure formation for several members of this family of proteins.

Preparation and Iron Redox Speciation Study of the Fe(II)-Binding Antimicrobial Protein Calprotectin

Calprotectin (CP, S100A8/S100A9 heterooligomer) is an abundant metal-sequestering host-defense protein expressed by neutrophils, other white blood cells, and epithelial cells. The apoprotein is a S100A8/S100A9 heterodimer that contains two sites for transition metal binding at the S100A8/S100A9 interface: a His₃Asp motif (site 1) and a His₆ motif (site 2). In this chapter, we provide a step-by-step protocol for the overexpression and purification of the human and murine orthologues of CP that affords each apo heterodimer in high yield and purity. In these procedures, the S100A8 and S100A9 subunits are overexpressed in Escherichia coli BL21(DE3), and each apo heterodimer is obtained following cell lysis, folding, column chromatography, and dialysis against Chelex resin to reduce metal contamination. Recent studies demonstrated that human CP coordinates Fe(II) and that the protein affects the redox speciation of Fe in solution. An Fe redox speciation assay employing ferrozine is described that demonstrates the ability of both the human and murine orthologues of CP to shift the redox speciation of Fe from the ferric to the ferrous oxidation state over time.

Oxidative Post-translational Modifications Accelerate Proteolytic Degradation of Calprotectin

Oxidative post-translational modifications affect the structure and function of many biomolecules. Herein we examine the biophysical and functional consequences of oxidative post-translational modifications to human calprotectin (CP, S100A8/S100A9 oligomer, MRP8/MRP14 oligomer, calgranulins A/B oligomer). This abundant metal-sequestering protein contributes to innate immunity by starving invading microbial pathogens of transition metal nutrients in the extracellular space. It also participates in the inflammatory response. Despite many decades of study, little is known about the fate of CP at sites of infection and inflammation. We present compelling evidence for methionine oxidation of CP in vivo, supported by using 15N-labeled CP-Ser (S100A8(C42S)/S100A9(C3S)) to monitor for adventitious oxidation following human sample collection. To elucidate the biochemical and functional consequences of oxidative post-translational modifications, we examine recombinant CP-Ser with methionine sulfoxide modifications generated by exposing the protein to hydrogen peroxide. These oxidized species coordinate transition metal ions and exert antibacterial activity. Nevertheless, oxidation of M81 in the S100A9 subunit disrupts Ca(II)-induced tetramerization and, in the absence of a transition metal ion bound at the His6 site, accelerates proteolytic degradation of CP. We demonstrate that native CP, which contains one Cys residue in each full-length subunit, forms disulfide bonds within and between S100A8/S100A9 heterodimers when exposed to hydrogen peroxide. Remarkably, disulfide bond formation accelerates proteolytic degradation of CP. We propose a new extension to the working model for extracellular CP where post-translational oxidation by reactive oxygen species generated during the neutrophil oxidative burst modulates its lifetime in the extracellular space.

Newly developed anti-S100A8/A9 monoclonal antibody efficiently prevents lung tropic cancer metastasis

The metastatic dissemination of cancer cells to remote areas of the body is the most problematic aspect in cancer patients. Among cancers, melanomas are notoriously difficult to treat due to their significantly high metastatic potential even during early stages. Hence, the establishment of advanced therapeutic approaches to regulate metastasis is required to overcome the melanoma disease. An accumulating mass of evidence has indicated a critical role of extracellular S100A8/A9 in melanoma distant metastasis. Lung S100A8/A9 is induced by melanoma cells from distant organs and it attracts these cells to its enriched lung environment since melanoma cells possess several receptors that sense the S100A8/A9 ligand. We hence aimed to develop a neutralizing antibody against S100A8/A9 that would efficiently block melanoma lung metastasis. Our protocol provided us with one prominent antibody, Ab45 that efficiently suppressed not only S100A8/A9-mediated melanoma mobility but also lung tropic melanoma metastasis in a mouse model. This prompted us to make chimeric Ab45, a chimera antibody consisting of mouse Ab45-Fab and human IgG2-Fc. Chimeric Ab45 also showed significant inhibition of the lung metastasis of melanoma. From these results, we have high hopes that the newly produced antibody will become a potential biological tool to block melanoma metastasis in future clinical settings.

S100A9 regulates cisplatin chemosensitivity of squamous cervical cancer cells and related mechanism

Objective

Our previous research has shown that the expression of S100 calcium-binding protein A9 (S100A9) in tumor cells was associated with neoadjuvant chemotherapy sensitivity in cervical squamous cell carcinoma. In the present study, we altered the expression of S100A9 through infecting lentivirus, investigated its effect on the chemosensitivity to cisplatin of cervical cancer cells and then made a primary exploration of the involved mechanism.

Materials and methods

Lentivirus was employed to upregulate and downregulate S100A9 expression in SiHa cells. The protein expression level of apoptotic-related proteins Bcl-2 and Bax, drug resistance-related proteins multiple drug resistance protein 1 (MRP1), P glycoprotein (P-gp), glutathione-S-transferase-π (GST-π), lung resistance-related protein (LRP), and FOXO1 signaling pathway related proteins was detected by Western blot. The CCK-8 assay was used to examine chemosensitivity to cisplatin, and the proportion of apoptosis cells was analyzed by the flow cytometry.

Results

S100A9 overexpression could obviously increase the IC50 value of SiHa cells to cisplatin and decrease the apoptosis rate induced by cisplatin. Downregulation of S100A9 led to the opposite results. In S100A9 overexpression SiHa cells, the expression level of Bcl-2, LRP, GST-π, p-AKT, p-ERK, p-FOXO1, and Nanog was significantly increased, while FOXO1 expression was decreased. The opposite results were observed in S100A9 knockdown SiHa cells.

Conclusion

Downregulation of S100A9 could significantly increase apoptosis rate, resulting in enhancing sensitivity of SiHa cells to cisplatin, which may be related to Bcl-2, GST-π, and LRP protein and by altering the AKT/ERK-FOXO1-Nanog signaling pathway.

Calprotectin (S100A8/S100A9): a key protein between inflammation and cancer

BACKGROUND

Calprotectin (S100A8/S100A9), a heterodimeric EF-hand Ca²⁺ binding protein, are abundant in cytosol of neutrophils and are involved in inflammatory processes and several cancerous pathogens.

OBJECTIVE

The purpose of the present systematic review is to evaluate the pro- and anti-tumorigenic functions of calprotectin and its relation to inflammation.

MATERIALS AND METHODS

We conducted a review of studies published in the Medline (1966-2018), Scopus (2004-2018), ClinicalTrials.gov (2008-2018) and Google Scholar (2004-2018) databases, combined with studies found in the reference lists of the included studies.

RESULTS

Elevated levels of S100A8/S100A9 were detected in inflammation, neoplastic tumor cells and various human cancers. Recent data have explained that many cancers arise from sites of infection, chronic irritation, and inflammation. The inflammatory microenvironment which largely includes calprotectin, has an essential role on high producing of inflammatory factors and then on neoplastic process and metastasis.

CONCLUSION

Scientists have shown different outcomes in inflammation, malignancy and apoptosis whether the source of the aforementioned protein is extracellular or intracellular. These findings are offering new insights that anti-inflammatory therapeutic agents and anti-tumorigenic functions of calprotectin can lead to control cancer development.

Biophysical Examination of the Calcium-Modulated Nickel-Binding Properties of Human Calprotectin Reveals Conformational Change in the EF-Hand Domains and His3Asp Site

Calprotectin (CP, S100A8/S100A9 oligomer, MRP-8/MRP-14 oligomer) is a host-defense protein that sequesters nutrient transition metals from microbes. Each S100A8/S100A9 heterodimer contains four EF-hand domains and two transition-metal-binding sites. We investigate the effect of Ca(II) ions on the structure and Ni(II)-binding properties of human CP. By employing energy dispersive X-ray (EDX) spectroscopy, we evaluate the metal content of Ni(II)-bound CP-Ser [oligomer of S100A8(C42S) and S100A9(C3S)] crystals obtained in the absence and presence of Ca(II). We present a 2.1 Å resolution crystal structure of Ni(II)-bound CP-Ser and compare this structure to a reported Ni(II)- and Ca(II)-bound CP-Ser structure [Nakashige, T. G., et al. (2017) J. Am. Chem. Soc. 139, 8828-8836]. This analysis reveals conformational changes associated with coordination of Ca(II) to the EF-hands of S100A9 and that Ca(II) binding affects the coordination number and geometry of the Ni(II) ion bound to the His3Asp site. In contrast, negligible differences are observed for the Ni(II)-His6 site in the absence and presence of Ca(II). Biochemical studies show that, whereas the His6 site has a thermodynamic preference for Ni(II) over Zn(II), the His3Asp site selects for Zn(II) over Ni(II), and relatively rapid metal exchange occurs at this site. These observations inform the working model for how CP withholds nutrient metals in the extracellular space.

Transition Metal Sequestration by the Host-Defense Protein Calprotectin

In response to microbial infection, the human host deploys metal-sequestering host-defense proteins, which reduce nutrient availability and thereby inhibit microbial growth and virulence. Calprotectin (CP) is an abundant antimicrobial protein released from neutrophils and epithelial cells at sites of infection. CP sequesters divalent first-row transition metal ions to limit the availability of essential metal nutrients in the extracellular space. While functional and clinical studies of CP have been pursued for decades, advances in our understanding of its biological coordination chemistry, which is central to its role in the host-microbe interaction, have been made in more recent years. In this review, we focus on the coordination chemistry of CP and highlight studies of its metal-binding properties and contributions to the metal-withholding innate immune response. Taken together, these recent studies inform our current model of how CP participates in metal homeostasis and immunity, and they provide a foundation for further investigations of a remarkable metal-chelating protein at the host-microbe interface and beyond.

Initial Biochemical and Functional Evaluation of Murine Calprotectin Reveals Ca(II)-Dependence and Its Ability to Chelate Multiple Nutrient Transition Metal Ions

Calprotectin (CP) is an abundant host-defense protein that contributes to the metal-withholding innate immune response by sequestering nutrient metal ions from microbial pathogens in the extracellular space. Over the past decade, murine models of infectious disease have advanced understanding of the physiological functions of CP and its ability to compete with microbes for essential metal nutrients. Despite this extensive work, murine CP (mCP) has not been biochemically evaluated, and structural and biophysical understanding of CP is currently limited to the human orthologue. We present the reconstitution, purification, and characterization of mCP as well as the cysteine-null variant mCP-Ser. Apo mCP is a mS100A8/mS100A9 heterodimer, and Ca(II) binding causes two heterodimers to self-associate and form a heterotetramer. Initial metal-depletion studies demonstrate that mCP depletes multiple first-row transition metal ions, including Mn, Fe, Ni, Cu, and Zn, from complex microbial growth medium, indicating that mCP binds multiple nutrient metals with high affinity. Moreover, antibacterial activity assays show that mCP inhibits the growth of a variety of bacterial species. The metal-depletion and antibacterial activity studies also provide evidence that Ca(II) ions enhance these functional properties of mCP. This contribution provides the groundwork for understanding the similarities and differences between the human and murine orthologues of CP and for further elucidation of its biological coordination chemistry.

Autoinhibitory regulation of S100A8/S100A9 alarmin activity locally restricts sterile inflammation

Autoimmune diseases, such as psoriasis and arthritis, show a patchy distribution of inflammation despite systemic dysregulation of adaptive immunity. Thus, additional tissue-derived signals, such as danger-associated molecular patterns (DAMPs), are indispensable for manifestation of local inflammation. S100A8/S100A9 complexes are the most abundant DAMPs in many autoimmune diseases. However, regulatory mechanisms locally restricting DAMP activities are barely understood. We now unravel for the first time, to our knowledge, a mechanism of autoinhibition in mice and humans restricting S100-DAMP activity to local sites of inflammation. Combining protease degradation, pull-down assays, mass spectrometry, and targeted mutations, we identified specific peptide sequences within the second calcium-binding EF-hands triggering TLR4/MD2-dependent inflammation. These binding sites are free when S100A8/S100A9 heterodimers are released at sites of inflammation. Subsequently, S100A8/S100A9 activities are locally restricted by calcium-induced (S100A8/S100A9)2 tetramer formation hiding the TLR4/MD2-binding site within the tetramer interphase, thus preventing undesirable systemic effects. Loss of this autoinhibitory mechanism in vivo results in TNF-α-driven fatal inflammation, as shown by lack of tetramer formation in crossing S100A9-/- mice with 2 independent TNF-α-transgene mouse strains. Since S100A8/S100A9 is the most abundant DAMP in many inflammatory diseases, specifically blocking the TLR4-binding site of active S100 dimers may represent a promising approach for local suppression of inflammatory diseases, avoiding systemic side effects.

Bioinorganic Explorations of Zn(II) Sequestration by Human S100 Host-Defense Proteins

The human innate immune system launches a metal-withholding response to starve invading microbial pathogens of essential metal nutrients. Zn(II)-sequestering proteins of the human S100 family contribute to this process and include calprotectin (CP, S100A8/S100A9 oligomer, calgranulin A/B oligomer), S100A12 (calgranulin C), and S100A7 (psoriasin). This Perspective highlights recent advances in the Zn(II) coordination chemistry of these three proteins, as well as select studies that evaluate Zn(II) sequestration as an antimicrobial mechanism.

Exploration of the platelet proteome in patients with early-stage cancer

Platelets play an important role in tumor growth and, at the same time, platelet characteristics are affected by cancer presence. Therefore, we investigated whether the platelet proteome harbors differentially expressed proteins associated with early-stage cancer. For this proof-of-concept study, patients with early-stage lung (n = 8) or head of pancreas cancer (n = 4) were included, as were healthy sex- and age-matched controls for both subgroups. Blood samples were collected from controls and from patients before surgery. Furthermore, from six of the patients, a second sample was collected two months after surgery. NanoLC-MS/MS-based proteomics of gel-fractionated platelet proteins was used for comparative spectral count analyses of patients to controls and before to after surgery samples. The total platelet proteome dataset included 4384 unique proteins of which 85 were significantly (criteria Fc > 1.5 and p < 0.05) changed in early-stage cancer compared to controls. In addition, the levels of 81 platelet proteins normalized after tumor resection. When filtering for the most discriminatory proteins, we identified seven promising platelet proteins associated with early-stage cancer. In conclusion, this pioneering study on the platelet proteome in cancer patients clearly identifies platelets as a new source of candidate protein biomarkers of early-stage cancer.

BIOLOGICAL SIGNIFICANCE

Currently, most blood-based diagnostics/biomarker research is performed in serum or plasma, while the content of blood cells is usually neglected. It is known that especially blood platelets, which are the main circulating pool of many bioactive proteins, such as growth factors, chemokines, and cytokines, are a potentially rich source of biomarkers. The current study is the first to measure the effect of early-stage cancer on the platelet proteome of patients. Our study demonstrates that the platelet proteome of patients with early-stage lung or head of pancreas cancer differs considerably compared to that of healthy individuals of matched sex and age. In addition, the platelet proteome of cancer patients normalized after surgical resection of the tumor. Exploiting platelet proteome differences linked to both tumor presence and disease status, we were able to demonstrate that the platelet proteome can be mined for potential biomarkers of cancer.

S100 Proteins As an Important Regulator of Macrophage Inflammation

The S100 proteins, a family of calcium-binding cytosolic proteins, have a broad range of intracellular and extracellular functions through regulating calcium balance, cell apoptosis, migration, proliferation, differentiation, energy metabolism, and inflammation. The intracellular functions of S100 proteins involve interaction with intracellular receptors, membrane protein recruitment/transportation, transcriptional regulation and integrating with enzymes or nucleic acids, and DNA repair. The S100 proteins could also be released from the cytoplasm, induced by tissue/cell damage and cellular stress. The extracellular S100 proteins, serving as a danger signal, are crucial in regulating immune homeostasis, post-traumatic injury, and inflammation. Extracellular S100 proteins are also considered biomarkers for some specific diseases. In this review, we will discuss the multi-functional roles of S100 proteins, especially their potential roles associated with cell migration, differentiation, tissue repair, and inflammation.

Calprotectin influences the aggregation of metal-free and metal-bound amyloid-β by direct interaction

CP-Ser [S100A8(C42S)/S100A9(C3S) oligomer] interacts with metal-free and metal-bound Aβ₄₀ peptides and modulates their aggregation in the absence and presence of metal ions.