Multiple structural states of S100A12: A key to its functional diversity

Calcium mediated static and dynamic allostery in S100A12: Implications for target recognition by S100 proteins

Structure and functions of S100 proteins are regulated by two distinct calcium binding EF hand motifs. In this work, we used solution-state NMR spectroscopy to investigate the cooperativity between the two calcium binding sites and map the allosteric changes at the target binding site. To parse the contribution of the individual calcium binding events, variants of S100A12 were designed to selectively bind calcium to either the EF-I (N63A) or EF-II (E31A) loop, respectively. Detailed analysis of the backbone chemical shifts for wildtype protein and its mutants indicates that calcium binding to the canonical EF-II loop is the principal trigger for the conformational switch between 'closed' apo to the 'open' Ca2+ -bound conformation of the protein. Elimination of binding in S100-specific EF-I loop has limited impact on the calcium binding affinity of the EF-II loop and the concomitant structural rearrangement. In contrast, deletion of binding in the EF-II loop significantly attenuates calcium affinity in the EF-I loop and the structure adopts a 'closed' apo-like conformation. Analysis of experimental amide nitrogen (15 N) relaxation rates (R1 , R2 , and 15 N-{1 H} NOE) and molecular dynamics (MD) simulations demonstrate that the calcium bound state is relatively floppy with pico-nanosecond motions induced in functionally relevant domains responsible for target recognition such as the hinge domain and the C-terminal residues. Experimental relaxation studies combined with MD simulations show that while calcium binding in the EF-I loop alone does not induce significant motions in the polypeptide chain, EF-I regulates fluctuations in the polypeptide in the presence of bound calcium in the EF-II loop. These results offer novel insights into the dynamic regulation of target recognition by calcium binding and unravels the role of cooperativity between the two calcium binding events in S100A12.

Temporal modelling of the biofilm lifecycle (TMBL) establishes kinetic analysis of plate-based bacterial biofilm dynamics

Bacterial biofilms are critical to pathogenesis and infection. They are associated with rising rates of antimicrobial resistance. Biofilms are correlated with worse clinical outcomes, making them important to infectious diseases research. There is a gap in knowledge surrounding biofilm kinetics and dynamics which makes biofilm research difficult to translate from bench to bedside. To address this gap, this work employs a well-characterized crystal violet biomass accrual and planktonic cell density assay across a clinically relevant time course and expands statistical analysis to include kinetic information in a protocol termed the TMBL (Temporal Mapping of the Biofilm Lifecycle) assay. TMBL's statistical framework quantitatively compares biofilm communities across time, species, and media conditions in a 96-well format. Measurements from TMBL can reliably be condensed into response features that inform the time-dependent behavior of adherent biomass and planktonic cell populations. Staphylococcus aureus and Pseudomonas aeruginosa biofilms were grown in conditions of metal starvation in nutrient-variable media to demonstrate the rigor and translational potential of this strategy. Significant differences in single-species biofilm formation are seen in metal-deplete conditions as compared to their controls which is consistent with the consensus literature on nutritional immunity that metal availability drives transcriptomic and metabolomic changes in numerous pathogens. Taken together, these results suggest that kinetic analysis of biofilm by TMBL represents a statistically and biologically rigorous approach to studying the biofilm lifecycle as a time-dependent process. In addition to current methods to study the impact of microbe and environmental factors on the biofilm lifecycle, this kinetic assay can inform biological discovery in biofilm formation and maintenance.

Pathogenic role of S100 proteins in psoriasis

Psoriasis is a chronic inflammatory skin disease. The histopathological features of psoriasis include excessive proliferation of keratinocytes and infiltration of immune cells. The S100 proteins are a group of EF-hand Ca2+-binding proteins, including S100A2, -A7, -A8/A9, -A12, -A15, which expression levels are markedly upregulated in psoriatic skin. These proteins exert numerous functions such as serving as intracellular Ca2+ sensors, transduction of Ca2+ signaling, response to extracellular stimuli, energy metabolism, and regulating cell proliferation and apoptosis. Evidence shows a crucial role of S100 proteins in the development and progress of inflammatory diseases, including psoriasis. S100 proteins can possibly be used as potential therapeutic target and diagnostic biomarkers. This review focuses on the pathogenic role of S100 proteins in psoriasis.

Inflammatory bowel disease biomarkers

Inflammatory bowel disease (IBD) is characterized as chronic inflammation in the gastrointestinal tract, which includes two main subtypes, Crohn's disease and ulcerative colitis. Endoscopy combined with biopsy is the most effective way to establish IBD diagnosis and disease management. Imaging techniques have also been developed to monitor IBD. Although effective, the methods are expensive and invasive, which leads to pain and discomfort. Alternative noninvasive biomarkers are being explored as tools for IBD prognosis and disease management. This review focuses on novel biomarkers that have emerged in recent years. These serological biomarkers and microRNAs could potentially be used for disease management in IBD, thereby decreasing patient discomfort and morbidity.

Calcium-binding proteins S100A8, S100A9, and S100A12: expression and regulation at the maternal-conceptus Interface in pigs†

Among the many calcium-binding proteins, S100A8, S100A9, and S100A12 play important roles in inflammation, innate immunity, and antimicrobial function, but their expression, regulation, and function at the maternal-conceptus interface in pigs are not fully understood. Therefore, we determined the expression and regulation of S100A8, S100A9, S100A12, and their receptor AGER at the maternal-conceptus interface in pigs. We found that S100A8, S100A9, and S100A12 mRNAs were expressed in the endometrium during the estrous cycle and pregnancy, with the greatest levels on Day (D) 12 of pregnancy, and AGER appeared at greater levels on D15 and D30 of pregnancy than on other days. The expression of S100A8, S100A9, and S100A12 was predominantly localized to epithelial cells in the endometrium, and they were detected in early-stage conceptus and later chorioallantoic tissues during pregnancy. AGER expression was localized to endometrial epithelial and stromal cells and chorionic epithelial cells. In endometrial explant tissues, the expression of S100A8, S100A9, and S100A12 was induced by estrogen, S100A8 by interleukin-1β, and AGER by interferon-γ. We further found that on D12 of pregnancy, the expression of S100A8, S100A9, and S100A12 decreased significantly in the endometria of gilts carrying conceptuses derived from somatic cell nuclear transfer. These results indicate that the expression of S100A8, S100A9, and S100A12 is dynamically regulated in response to conceptus-derived signals at the maternal-conceptus interface, suggesting that S100A8, S100A9, and S100A12 could play a critical role in regulating endometrial epithelial cell function and conceptus implantation to support the establishment and maintenance of pregnancy in pigs.

Characterization and engineering of S100A12-heparan sulfate interactions

S100A12, an EF-hand calcium-binding protein, can be secreted by a variety of cell types and plays proinflammatory roles in a number of pathological conditions. Although S100A12 has been shown to interact with heparan sulfate (HS), the molecular detail of the interaction remains unclear. Here we investigate the structural basis of S100A12-HS interaction and how the interaction is regulated by the availability of divalent cations and the oligomeric states of S100A12. We discovered that S100A12-HS interaction requires calcium, while zinc can further enhance binding by inducing S100A12 hexamerization. In contrast, the apo form and zinc-induced tetramer form were unable to bind HS. Guided by the crystal structures of S100A12, we have identified the HS-binding site of S100A12 by site-directed mutagenesis. Characterization of the HS-binding site of S100A12 allowed us to convert the non-HS-binding apo and tetramer forms of S100A12 into a high affinity HS-binding variant by engineering a single-point mutation. Using a HS oligosaccharide microarray, we demonstrated that the N43K mutant displayed markedly enhanced selectivity toward longer HS oligosaccharides compared to the WT S100A12, likely due to the expanded dimension of the reengineered HS-binding site in the mutant. This unexpected finding strongly suggests that HS-binding sites of proteins might be amenable for engineering.

Discerning the promising binding sites of S100/calgranulins and their therapeutic potential in atherosclerosis

INTRODUCTION

Atherosclerosis is a chronic inflammatory disease in which the members of S100 family proteins (calgranulins) bind with their receptors, particularly receptor for advanced glycation end products (RAGE) and toll-like receptor-4 (TLR-4) and play a key role in the pathogenesis and progression of disease. Thus, these proteins could be considered as potential biomarkers and therapeutic targets in the treatment of atherosclerotic inflammation.

AREAS COVERED

This review summarizes the pathology of S100A8, S100A9, and S100A12 in the development of atherosclerosis and reveals key structural features of these proteins which are potentially critical in their pathological effects. This article focuses on the translational significance of antagonizing these proteins by using small molecules in patent literature, clinical and preclinical studies and also discusses future approaches that could be employed to block these proteins in the treatment of atherosclerosis.

EXPERT OPINION

Based on the critical role of S100/calgranulins in the regulation of atherosclerosis, these proteins are potential targets to develop better therapeutic options in the treatment of inflammatory diseases. However, further research is still needed to clarify their exact molecular mechanism by analyzing their detailed structural features that can expedite future research to develop novel therapeutics against these proteins to treat atherosclerotic inflammation.

Application of Salivary Biomarkers in the Diagnosis of Fibromyalgia

Fibromyalgia (FM) is a highly prevalent syndrome that impairs the quality of life of the patients; however, its diagnosis is complex and mainly centered on pain symptoms. The study of salivary biomarkers has proven highly useful for the diagnosis and prognosis of numerous diseases. The objective of this review was to gather published data on the utilization of salivary biomarkers to facilitate and complement the diagnosis of FM. Salivary biomarkers used in FM diagnosis include cortisol; calgranulin; and the enzymes α-amylase, transaldolase, and phosphoglycerate mutase. Increased serum levels of C-reactive protein, cytokines interleukin 1-β, interleukin 6, interleukin 8, interleukin 10, interleukin 17, tumor necrosis factor α, and various chemokines may serve as salivary biomarkers, given observations of their increased serum levels in patients with FM. Further research is warranted to study in depth the role and performance of biomarkers currently used in FM diagnosis/prognosis and to identify novel salivary biomarkers for this disease.

S100A12 in Digestive Diseases and Health: A Scoping Review

Calgranulin proteins are an important class of molecules involved in innate immunity. These members of the S100 class of the EF-hand family of calcium-binding proteins have numerous cellular and antimicrobial functions. One protein in particular, S100A12 (also called EN-RAGE or calgranulin C), is highly abundant in neutrophils during acute inflammation and has been implicated in immune regulation. Structure-function analyses reveal that S100A12 has the capacity to bind calcium, zinc, and copper, processes that contribute to nutritional immunity against invading microbial pathogens. S100A12 is a ligand for the receptor for advanced glycation end products (RAGE), toll-like receptor 4 (TLR4), and CD36, which promote cellular and immunological pathways to alter inflammation. We conducted a scoping review of the existing literature to define what is known about the association of S100A12 with digestive disease and health. Results suggest that S100A12 is implicated in gastroenteritis, necrotizing enterocolitis, gastritis, gastric cancer, Crohn's disease, irritable bowel syndrome, inflammatory bowel disease, and digestive tract cancers. Together, these results reveal S100A12 is an important molecule broadly associated with the pathogenesis of digestive diseases.

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.

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.

Expression, Purification, and Antimicrobial Activity of S100A12

Calgranulin proteins are important mediators of innate immunity and are members of the S100 class of the EF-hand family of calcium binding proteins. Some S100 proteins have the capacity to bind transition metals with high affinity and effectively sequester them away from invading microbial pathogens in a process that is termed "nutritional immunity". S100A12 (EN-RAGE) binds both zinc and copper and is highly abundant in innate immune cells such as macrophages and neutrophils. We report a refined method for the expression, enrichment and purification of S100A12 in its active, metal-binding configuration. Utilization of this protein in bacterial growth and viability analyses reveals that S100A12 has antimicrobial activity against the bacterial pathogen, Helicobacter pylori. The antimicrobial activity is predicated on the zinc-binding activity of S100A12, which chelates nutrient zinc, thereby starving H. pylori which requires zinc for growth and proliferation.

The self-association of HMGB1 and its possible role in the binding to DNA and cell membrane receptors

High mobility group box 1 (HMGB1), a chromatin protein, interacts with DNA and controls gene expression. However, when HMGB1 is released from apoptotic or damaged cells, it triggers proinflammatory reactions by interacting with various receptors, mainly receptor for advanced glycation end-products (RAGE) and toll-like receptors (TLRs). The self-association of HMGB1 has been found to be crucial for its DNA-related biological functions. It is influenced by several factors, such as ionic strength, pH, specific divalent metal cations, redox environment and acetylation. This self-association may also play a role in the interaction with RAGE and TLRs and the concomitant inflammatory responses. Future studies should address the potential role of HMGB1 self-association on its interactions with DNA, RAGE and TLRs, as well as the influence of physicochemical factors in different cellular environments on these interactions.

S100A12 Induced in the Epidermis by Reduced Hydration Activates Dermal Fibroblasts and Causes Dermal Fibrosis

Disruption of the barrier function of skin increases transepidermal water loss and up-regulates inflammatory pathways in the epidermis. Consequently, sustained expression of proinflammatory cytokines from the epidermis is associated with dermal scarring. We found increased expression of S100A12 in the epidermis of human hypertrophic and keloid scar. Exposing a stratified keratinocyte culture to a reduced-hydration environment increased the expression and secretion of S100A12 by nearly 70%, which in turn activated dermal fibroblasts in vitro. Direct treatment of fibroblasts with conditioned medium collected from stratified keratinocyte culture under reduced-hydration conditions activated fibroblasts, shown by up-regulation of α-smooth muscle actin, pro-collagen 1, and F-actin expression. However, this fibroblast activation was not found when S100A12 was knocked down by RNA interference in keratinocytes. Pharmacological blockade of S100A12 receptors, RAGE, or TLR4 inhibited S100A12-induced fibroblast activation. Local delivery of S100A12 resulted in a marked hypertrophic scar formation in a validated rabbit hypertrophic scar model compared with saline control. Our findings indicate that S100A12 functions as a proinflammatory cytokine and suggest that S100A12 is a potential therapeutic target for dermal scarring.

Blocking the Interactions between Calcium-Bound S100A12 Protein and the V Domain of RAGE Using Tranilast

The receptor for advanced glycation end products (RAGE), a transmembrane receptor in the immunoglobulin superfamily, is involved in several inflammatory processes. RAGE induces cellular signaling pathways upon binding with various ligands, such as advanced glycation end products (AGEs), β-amyloids, and S100 proteins. The solution structure of S100A12 and the V ligand-binding region of RAGE have been reported previously. Using heteronuclear NMR spectroscopy to conduct ¹H–¹⁵N heteronuclear single quantum coherence (HSQC) titration experiments, we identified and mapped the binding interface between S100A12 and the V domain of RAGE. The NMR chemical shift data were used as the constraints for the High Ambiguity Driven biomolecular DOCKing (HADDOCK) calculation to generate a structural model of the S100A12–V domain complex. In addition, tranilast (an anti-allergic drug) showed strong interaction with S100A12 in the ¹H–¹⁵N HSQC titration, fluorescence experiments, and WST-1 assay. The results also indicated that tranilast was located at the binding site between S100A12 and the V domain, blocking interaction between these two proteins. Our results provide the mechanistic details for a structural model and reveal a potential precursor for an inhibitor for pro-inflammatory diseases, which could be useful for the development of new drugs.

The effect of physicochemical factors on the self-association of HMGB1: A surface plasmon resonance study

HMGB1 triggers proinflammatory reactions by interacting extracellularly with various receptors. HMGB1 also acts in the nucleus by interacting with DNA and controlling DNA transcription, a process which involves its self-association. The self-association of HMGB1 was characterized using surface plasmon resonance (SPR). A dimer/tetramer binding model was developed that provided a good fit to the SPR sensorgrams and enabled the kinetics of self-association of different HMGB1 oligomers to be evaluated under a variety of physicochemical conditions. The formation of HMGB1 tetramers, and not dimers, was strongly influenced by ionic strength. HMGB1 self-association increased as the pH was decreased from 7.4 to 4.8 but was abolished at pH4.0, suggesting the involvement of acidic amino acids of HMGB1 in its self-association. HMGB1 dimers were found to predominate in the absence of zinc, but addition of zinc promoted the formation of HMGB1 tetramers. More reducing conditions favored dimerization but diminished tetramer formation. In contrast, oxidizing conditions favored tetramer formation. Physicochemical factors modulate the extent of self-association of HMGB1. We speculate that HMGB1 dimers may preferentially bind DNA, whereas HMGB1 tetramers may promote inflammatory responses by binding to RAGE and TLRs. The self-association of HMGB1, regulated by variations of physicochemical factors, may influence its roles in DNA rearrangement and regulation of pathophysiological diseases.

New structural insights into Golgi Reassembly and Stacking Protein (GRASP) in solution

Among all proteins localized in the Golgi apparatus, a two-PDZ (PSD95/DlgA/Zo-1) domain protein plays an important role in the assembly of the cisternae. This Golgi Reassembly and Stacking Protein (GRASP) has puzzled researchers due to its large array of functions and relevance in Golgi functionality. We report here a biochemical and biophysical study of the GRASP55/65 homologue in Cryptococcus neoformans (CnGRASP). Bioinformatic analysis, static fluorescence and circular dichroism spectroscopies, calorimetry, small angle X-ray scattering, solution nuclear magnetic resonance, size exclusion chromatography and proteolysis assays were used to unravel structural features of the full-length CnGRASP. We detected the coexistence of regular secondary structures and large amounts of disordered regions. The overall structure is less compact than a regular globular protein and the high structural flexibility makes its hydrophobic core more accessible to solvent. Our results indicate an unusual behavior of CnGRASP in solution, closely resembling a class of intrinsically disordered proteins called molten globule proteins. To the best of our knowledge, this is the first structural characterization of a full-length GRASP and observation of a molten globule-like behavior in the GRASP family. The possible implications of this and how it could explain the multiple facets of this intriguing class of proteins are discussed.

Calcium Ions Tune the Zinc-Sequestering Properties and Antimicrobial Activity of Human S100A12

Human S100A12 is a host-defense protein expressed and released by neutrophils that contributes to innate immunity. Apo S100A12 is a 21-kDa antiparallel homodimer that harbors two Ca(II)-binding EF-hand domains per subunit and exhibits two His3Asp motifs for chelating transition metal ions at the homodimer interface. In this work, we present results from metal-binding studies and microbiology assays designed to ascertain whether Ca(II) ions modulate the Zn(II)-binding properties of S100A12 and further evaluate the antimicrobial properties of this protein. Our metal depletion studies reveal that Ca(II) ions enhance the ability of S100A12 to sequester Zn(II) from microbial growth media. We report that human S100A12 has antifungal activity against Candida albicans, C. krusei, C. glabrata and C. tropicalis, all of which cause human disease. This antifungal activity is Ca(II)-dependent and requires the His3Asp metal-binding sites. We expand upon prior studies of the antibacterial activity of S100A12 and report Ca(II)-dependent and strain-selective behavior. S100A12 exhibited in vitro growth inhibitory activity against Listeria monocytogenes. In contrast, S100A12 had negligible effect on the growth of Escherichia coli K-12 and Pseudomonas aeruginosa PAO1. Loss of functional ZnuABC, a high-affinity Zn(II) import system, increased the susceptibility of E. coli and P. aeruginosa to S100A12, indicating that S100A12 deprives these mutant strains of Zn(II). To evaluate the Zn(II)-binding sites of S100A12 in solution, we present studies using Co(II) as a spectroscopic probe and chromophoric small-molecule chelators in Zn(II) competition titrations. We confirm that S100A12 binds Zn(II) with a 2:1 stoichiometry, and our data indicate sub-nanomolar affinity binding. Taken together, these data support a model whereby S100A12 uses Ca(II) ions to tune its Zn(II)-chelating properties and antimicrobial activity.

Metal ion homeostasis in Listeria monocytogenes and importance in host-pathogen interactions

Listeria monocytogenes is responsible for one of the most life-threatening food-borne infections and the leading cause of food-poisoning associated deaths in the UK. Infection may be of the unborn/newly born infant where disease may manifest as listeric abortion, stillbirth or late-onset neonatal listeriosis, while in adults, infection usually affects the central nervous system causing meningitis. Crucial to the survival of L. monocytogenes, both inside and outside the host, is its ability to acquire metals which act as cofactors for a broad range of its cellular proteins. However, L. monocytogenes must also protect itself against the innate toxicity of metals. The importance of metals in host-pathogen interactions is illustrated by the restriction of metals (including zinc and iron) in vertebrates in response to infection and the use of high levels of metals (copper and zinc) as part of the antimicrobial defences within host phagocytes. As such, L. monocytogenes is equipped with various mechanisms to tightly control its cellular metal pools and avoid metal poisoning. These include multiple DNA-binding metal-responsive transcription factors, metal-acquisition, metal-detoxification and metal-storage systems, some of which represent key L. monocytogenes virulence determinants. This review discusses current knowledge of the role of metals in L. monocytogenes infections, with a focus on the mechanisms that contribute to zinc and copper homeostasis in this organism. The requirement to precisely control cellular metal levels may impose a vulnerability to L. monocytogenes which can be exploited in antimicrobials and therapeutics.

In silico assessment of S100A12 monomer and dimer structural dynamics: implications for the understanding of its metal-induced conformational changes

Changes in the concentration of different ions modulate several cellular processes, such as Ca(2+) and Zn(2+) in inflammation. Upon activation of immune system effector cells, the intracellular Ca(2+) concentration rises propagating the activation signal, leading to degranulation and generation of reactive oxygen species, which increases the Zn(2+) intracellular concentration as a consequence of the cellular antioxidant machinery. In this context, S100A12 is of special interest because it is a pro-inflammatory protein expressed in neutrophils whose structure and function are modulated by both Ca(2+) and Zn(2+). The current hypothesis about its mechanism of action was built based on biochemical and crystallographic data. However, there are missing connections between molecular structure and the way in which many events are concatenated at the triggering and along the inflammatory process. In this work we use molecular dynamics simulations to describe how variations in Zn(2+) and Ca(2+) concentrations modulate the structural dynamics of the calcium-free S100A12 dimer and monomer, which was not considered a part of the mechanism of action before. Our results suggest that (i) Zn(2+) have a determinant role in the dimerization step, as well as in the unbinding of the Na(+) complexed to the N-terminal EF-hand; (ii) the N-terminal EF-hand domain is the first to bind Ca(2+), and not the C-terminal, as usually accepted; and that (iii) Ca(2+) modulates the structural dynamics of H-III.

Expression of receptor for advanced glycation end products (RAGE) on the surface of circulating endothelial cells is upregulated in Kawasaki disease

INTRODUCTION

The aim of this study was to investigate the expression of receptor for advanced glycation end products (RAGE) on the surface of circulating endothelial cells (CECs) in patients with Kawasaki disease (KD).

METHODS

The positive rate of RAGE on the surface of CECs (CECs-RAGE/CECs) and the fluorescence intensity of RAGE on the surface of CECs (FI-RAGE-CECs) were evaluated in 89 patients with KD in the acute stage (A-KD), subacute stage (SA-KD), or convalescent stage (C-KD).

RESULTS

CECs-RAGE/CECs and the FI-RAGE-CECs increased significantly in patients with KD. The CECs-RAGE/CECs was significantly higher in C-KD patients with coronary artery lesions (CALs) than in those without CALs. The FI-RAGE-CECs level was significantly higher in SA-KD and C-KD patients with CALs than in A-KD patients. In SA-KD and C-KD patients, the CECs-RAGE/CECs and FI-RAGE-CECs levels decreased in intravenous immunoglobulin (IVIG)-respondent patients but increased progressively in IVIG-resistant patients and were significantly higher in IVIG-resistant patients than in IVIG-respondent patients.

DISCUSSION

The results suggest that the expression levels of RAGE on the surface of CECs are upregulated in KD patients, and that the upregulated expression levels of RAGE on the surface of CECs can be aggravated in SA-KD and C-KD patients with CALs, and also in IVIG-resistant SA-KD and C-KD patients. The RAGE expression on CECs is involved in the pathophysiology of KD.

EN-RAGE (extracellular newly identified receptor for advanced glycation end-products binding protein) and mortality of long-term hemodialysis patients: A prospective observational cohort study

OBJECTIVES

EN-RAGE is extracellular newly identified receptor for advanced glycation end-products binding protein playing a role in inflammation. The aim was to test the relationship of EN-RAGE to prognosis of long-term hemodialysis patients (HD).

DESIGN AND METHODS

This is a prospective observational cohort study in 261 HD patients followed up for five years. Laboratory parameters were measured at the beginning of the study.

RESULTS

EN-RAGE was slightly but unsignificantly increased in HD patients compared with healthy controls and correlated significantly with inflammatory markers. Univariate Cox analysis demonstrated EN-RAGE as a significant predictor for mortality due to infection (HR (95%CI): 1.305 (1.063-1.602), per standard deviation, p=0.01), but this significance disappeared in multivariate Cox analysis when CRP was included into the model.

CONCLUSIONS

Our study demonstrates EN-RAGE as an inflammatory biomarker. It is related to mortality of HD patients due to infection, but in our study, it did not provide additional information to CRP.

Plasma S100A12 level is associated with cardiovascular disease in hemodialysis patients

BACKGROUND AND OBJECTIVES

S100A12 is an endogenous receptor ligand for advanced glycation end products. Cardiovascular disease remains a major cause of morbidity and mortality in patients with chronic kidney disease. In this study, we report cross-sectional data on 550 hemodialysis patients and assess the relationship between plasma S100A12 level and cardiovascular disease.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A cross-sectional study of 550 maintenance hemodialysis patients was conducted. We investigated the past history of cardiovascular disease and quantified the plasma level of S100A12 protein in all participants.

RESULTS

Plasma S100A12 level was higher in hemodialysis patients with cardiovascular disease (n=197; 33.8 ± 28.1 ng/ml) than in those without it (n=353; 20.2 ± 16.1 ng/ml; P<0.001). In multivariate logistic regression analysis, the plasma S100A12 level (odds ratio [OR], 1.28; 95% confidence interval [CI], 1.13 to 1.44; P<0.001) was identified as an independent factor associated with the prevalence of cardiovascular disease. The other factors associated with the prevalence of cardiovascular diseases were the presence of diabetes mellitus (OR, 2.81; 95% CI, 1.79 to 4.41; P < 0.001) and high-sensitivity CRP level (OR, 1.02; 95% CI, 1.00 to 1.05; P=0.046). Furthermore, the plasma S100A12 level (OR, 1.30; 95% CI, 1.09 to 1.54; P=0.004) was significantly associated with cardiovascular disease even in hemodialysis patients without diabetes mellitus (n=348).

CONCLUSIONS

These results suggest that the plasma S100A12 protein level is strongly associated with the prevalence of cardiovascular disease in hemodialysis patients.

Carboxylated N-glycans on RAGE promote S100A12 binding and signaling

The receptor for advanced glycation end products (RAGE) is a signaling receptor protein of the immunoglobulin superfamily implicated in multiple pathologies. It binds a diverse repertoire of ligands, but the structural basis for the interaction of different ligands is not well understood. We earlier showed that carboxylated glycans on the V-domain of RAGE promote the binding of HMGB1 and S100A8/A9. Here we study the role of these glycans on the binding and intracellular signaling mediated by another RAGE ligand, S100A12. S100A12 binds carboxylated glycans, and a subpopulation of RAGE enriched for carboxylated glycans shows more than 10-fold higher binding potential for S100A12 than total RAGE. When expressed in mammalian cells, RAGE is modified by complex glycans predominantly at the first glycosylation site (N25IT) that retains S100A12 binding. Glycosylation of RAGE and maximum binding sites for S100A12 on RAGE are also cell type dependent. Carboxylated glycan-enriched population of RAGE forms higher order multimeric complexes with S100A12, and this ability to multimerize is reduced upon deglycosylation or by using non-glycosylated sRAGE expressed in E. coli. mAbGB3.1, an antibody against carboxylated glycans, blocks S100A12-mediated NF-kappaB signaling in HeLa cells expressing full-length RAGE. These results demonstrate that carboxylated N-glycans on RAGE enhance binding potential and promote receptor clustering and subsequent signaling events following oligomeric S100A12 binding.

The Calcium-Dependent Interaction of S100B with Its Protein Targets

S100B is a calcium signaling protein that is a member of the S100 protein family. An important feature of S100B and most other S100 proteins (S100s) is that they often bind Ca²⁺ ions relatively weakly in the absence of a protein target; upon binding their target proteins, Ca²⁺-binding then increases by as much as from 200- to 400-fold. This manuscript reviews the structural basis and physiological significance of increased Ca²⁺-binding affinity in the presence of protein targets. New information regarding redundancy among family members and the structural domains that mediate the interaction of S100B, and other S100s, with their targets is also presented. It is the diversity among individual S100s, the protein targets that they interact with, and the Ca²⁺ dependency of these protein-protein interactions that allow S100s to transduce changes in [Ca²⁺]_{intracellular} levels into spatially and temporally unique biological responses.

The S100B/RAGE Axis in Alzheimer's Disease

Increasing evidence suggests that the small EF-hand calcium-binding protein S100B plays an important role in Alzheimer's disease. Among other evidences are the increased levels of both S100B and its receptor, the Receptor for Advanced Glycation Endproducts (RAGEs) in the AD diseased brain. The regulation of RAGE signaling by S100B is complex and probably involves other ligands including the amyloid beta peptide (Aβ), the Advanced Glycation Endproducts (AGEs), or transtheyretin. In this paper we discuss the current literature regarding the role of S100B/RAGE activation in Alzheimer's disease.

ANTI-INFECTIVE PROTECTIVE PROPERTIES OF S100 CALGRANULINS

The calgranulins are a subgroup of proteins in the S100 family (calgranulin A, S100A8; calgranulin B, S100A9 and calgranulin C, S100A12) that provide protective anti-infective and anti-inflammatory functions for the mammalian host. In this review, we discuss the structure-function relationships whereby S100A8 and S100A9, and for comparison, S100A12, provide intra- and extracellular protection during the complex interplay between infection and inflammation and how the calgranulins are regulated to optimally protect the host. Ideally located to support epithelial barrier function, calprotectin, a complex of S100A8/S100A9, is expressed in squamous mucosal keratinocytes and innate immune cells present at mucosal surfaces. The calgranulins are also abundantly produced in neutrophils and monocytes, whereas expression is induced in epidermal keratinocytes, gastrointestinal epithelial cells and fibroblasts during inflammation. The calgranulins show species-specific expression and function. For example, S100A8 is chemotactic in rodents but not in humans. In humans, S100A12 appears to serve as a functional chemotactic homolog to murine S100A8. Transition metal-binding and oxidation sites within calgranulins are able to create structural changes that may orchestrate new protective functions or binding targets. The calgranulins thus appear to adopt a variety of roles to protect the host. In addition to serving as a leukocyte chemoattractant, protective functions include oxidant scavenging, antimicrobial activity, and chemokine-like activities. Each function may reflect the concentration of the calgranulin, post-transcriptional modifications, oligomeric forms, and the proximal intracellular or extracellular environments. Calprotectin and the calgranulins are remarkable as multifunctional proteins dedicated to protecting the intra- and extracellular environments during infection and inflammation.

S100A8/A9: a Janus-faced molecule in cancer therapy and tumorgenesis

Correlations exist between the abundance of S100 proteins and disease pathologies. Indeed, this is evidenced by the heterodimeric S100 protein complex S100A8/A9 which has been shown to be involved in inflammatory and neoplastic disorders. However, S100A8/A9 appears as a Janus-faced molecule in this context. On the one hand, it is a powerful apoptotic agent produced by immune cells, making it a very fascinating tool in the battle against cancer. It spears the risk to induce auto-immune response and may serve as a lead compound for cancer-selective therapeutics. In contrast, S100A8/A9 expression in cancer cells has also been associated with tumor development, cancer invasion or metastasis. Clearly, there is a dichotomy and future investigations into the role of S100A8/A9 in cancer biology need to consider both sides of the same coin.

RAGE (Receptor for Advanced Glycation Endproducts), RAGE ligands, and their role in cancer and inflammation

The Receptor for Advanced Glycation Endproducts [RAGE] is an evolutionarily recent member of the immunoglobulin super-family, encoded in the Class III region of the major histocompatability complex. RAGE is highly expressed only in the lung at readily measurable levels but increases quickly at sites of inflammation, largely on inflammatory and epithelial cells. It is found either as a membrane-bound or soluble protein that is markedly upregulated by stress in epithelial cells, thereby regulating their metabolism and enhancing their central barrier functionality. Activation and upregulation of RAGE by its ligands leads to enhanced survival. Perpetual signaling through RAGE-induced survival pathways in the setting of limited nutrients or oxygenation results in enhanced autophagy, diminished apoptosis, and (with ATP depletion) necrosis. This results in chronic inflammation and in many instances is the setting in which epithelial malignancies arise. RAGE and its isoforms sit in a pivotal role, regulating metabolism, inflammation, and epithelial survival in the setting of stress. Understanding the molecular structure and function of it and its ligands in the setting of inflammation is critically important in understanding the role of this receptor in tumor biology.

Binding of S100 proteins to RAGE: an update

The Receptor for Advanced Glycation Endproducts (RAGE) is a multi-ligand receptor of the immunoglobulin family. RAGE interacts with structurally different ligands probably through the oligomerization of the receptor on the cell surface. However, the exact mechanism is unknown. Among RAGE ligands are members of the S100 protein family. S100 proteins are small calcium binding proteins with high structural homology. Several members of the family have been shown to interact with RAGE in vitro or in cell-based assays. Interestingly, many RAGE ligands appear to interact with distinct domains of the extracellular portion of RAGE and to trigger various cellular effects. In this review, we summarize the modes of S100 protein-RAGE interaction with regard to their cellular functions.

S100B's double life: intracellular regulator and extracellular signal

The Ca2+-binding protein of the EF-hand type, S100B, exerts both intracellular and extracellular functions. Recent studies have provided more detailed information concerning the mechanism(s) of action of S100B as an intracellular regulator and an extracellular signal. Indeed, intracellular S100B acts as a stimulator of cell proliferation and migration and an inhibitor of apoptosis and differentiation, which might have important implications during brain, cartilage and skeletal muscle development and repair, activation of astrocytes in the course of brain damage and neurodegenerative processes, and of cardiomyocyte remodeling after infarction, as well as in melanomagenesis and gliomagenesis. As an extracellular factor, S100B engages RAGE (receptor for advanced glycation end products) in a variety of cell types with different outcomes (i.e. beneficial or detrimental, pro-proliferative or pro-differentiative) depending on the concentration attained by the protein, the cell type and the microenvironment. Yet, RAGE might not be the sole S100B receptor, and S100B's ability to engage RAGE might be regulated by its interaction with other extracellular factors. Future studies using S100B transgenic and S100B null mice might shed more light on the functional role(s) of the protein.

Metastasis promoter S100A4 is a potentially valuable molecular target for cancer therapy

The growth, invasion and metastatic spread of cancer have been identified with the deregulation of cell proliferation, altered intercellular and cell-substratum adhesion and enhanced motility and the deposition of disseminated cancer cells at distant sites. The identification of therapeutic targets for cancer is crucial to human welfare. Drug development, molecular modelling and design of effective drugs greatly depend upon the identification of suitable therapeutic targets. Several genetic determinants relating to proliferation and growth, invasion and metastasis have been identified. S100A4 appears to be able to activate and integrate pathways to generate the phenotypic responses that are characteristic of cancer. S100A4 signalling can focus on factors associated with normal and aberrant proliferation, apoptosis and growth, and differentiation. It is able to activate signalling pathways leading to the remodelling of the cell membrane and the extracellular matrix; modulation of cytoskeletal dynamics, acquisition of invasiveness and induction of angiogenesis. Therefore S100A4 is arguably a molecular target of considerable potential possessing a wide ranging biological activity that can alter and regulate the major phenotypic features of cancer. The evolution of an appropriate strategy that permits the identification of therapeutic targets most likely to be effective in the disease process without unduly affecting normal biological processes and function is an incontrovertible imperative. By virtue of its ability to activate interacting and multi-functional signalling systems, S100A4 appears to offer suitable targets for developing new therapeutic procedures. Some effectors of the S100A4-activated pathways might also lend themselves as foci of therapeutic interest.

Divalent metal ion complexes of S100B in the absence and presence of pentamidine

As part of an effort to inhibit S100B, structures of pentamidine (Pnt) bound to Ca(2+)-loaded and Zn(2+),Ca(2+)-loaded S100B were determined by X-ray crystallography at 2.15 A (R(free)=0.266) and 1.85 A (R(free)=0.243) resolution, respectively. These data were compared to X-ray structures solved in the absence of Pnt, including Ca(2+)-loaded S100B and Zn(2+),Ca(2+)-loaded S100B determined here (1.88 A; R(free)=0.267). In the presence and absence of Zn(2+), electron density corresponding to two Pnt molecules per S100B subunit was mapped for both drug-bound structures. One Pnt binding site (site 1) was adjacent to a p53 peptide binding site on S100B (+/-Zn(2+)), and the second Pnt molecule was mapped to the dimer interface (site 2; +/-Zn(2+)) and in a pocket near residues that define the Zn(2+) binding site on S100B. In addition, a conformational change in S100B was observed upon the addition of Zn(2+) to Ca(2+)-S100B, which changed the conformation and orientation of Pnt bound to sites 1 and 2 of Pnt-Zn(2+),Ca(2+)-S100B when compared to Pnt-Ca(2+)-S100B. That Pnt can adapt to this Zn(2+)-dependent conformational change was unexpected and provides a new mode for S100B inhibition by this drug. These data will be useful for developing novel inhibitors of both Ca(2+)- and Ca(2+),Zn(2+)-bound S100B.

Identification of immune genes and proteins involved in the response of bovine mammary tissue to Staphylococcus aureus infection

BACKGROUND

Mastitis in dairy cattle results from infection of mammary tissue by a range of micro-organisms but principally coliform bacteria and Gram positive bacteria such as Staphylococcus aureus. The former species are often acquired by environmental contamination while S. aureus is particularly problematic due to its resistance to antibiotic treatments and ability to reside within mammary tissue in a chronic, subclinical state. The transcriptional responses within bovine mammary epithelial tissue subjected to intramammary challenge with S. aureus are poorly characterised, particularly at the earliest stages of infection. Moreover, the effect of infection on the presence of bioactive innate immune proteins in milk is also unclear. The nature of these responses may determine the susceptibility of the tissue and its ability to resolve the infection.

RESULTS

Transcriptional profiling was employed to measure changes in gene expression occurring in bovine mammary tissues sampled from three dairy cows after brief and graded intramammary challenges with S. aureus. These limited challenges had no significant effect on the expression pattern of the gene encoding beta-casein but caused coordinated up-regulation of a number of cytokines and chemokines involved in pro-inflammatory responses. In addition, the enhanced expression of two genes, S100 calcium-binding protein A12 (S100A12) and Pentraxin-3 (PTX3) corresponded with significantly increased levels of their proteins in milk from infected udders. Both genes were shown to be expressed by mammary epithelial cells grown in culture after stimulation with lipopolysaccharide. There was also a strong correlation between somatic cell count, a widely used measure of mastitis, and the level of S100A12 in milk from a herd of dairy cows. Recombinant S100A12 inhibited growth of Escherichia coli in vitro and recombinant PTX3 bound to E. coli as well as C1q, a subunit of the first component of the complement cascade.

CONCLUSION

The transcriptional responses in infected bovine mammary tissue, even at low doses of bacteria and short periods of infection, probably reflect the combined contributions of gene expression changes resulting from the activation of mammary epithelial cells and infiltrating immune cells. The secretion of a number of proinflammatory cytokines and chemokines from mammary epithelial cells stimulated by the bacteria serves to trigger the recruitment and activation of neutrophils in mammary tissue. The presence of S100A12 and PTX3 in milk from infected udder quarters may increase the anti-bacterial properties of milk thereby helping to resolve the mammary tissue infection as well as potentially contributing to the maturation of the newborn calf epithelium and establishment of the newborn gut microbial population.

Mast cell and monocyte recruitment by S100A12 and its hinge domain

S100A12 is expressed at sites of acute, chronic, and allergic inflammation. S100 proteins have regions of high sequence homology, but the "hinge" region between the conserved calcium binding domains is structurally and functionally divergent. Because the murine S100A8 hinge domain (mS100A8(42-55)) is a monocyte chemoattractant whereas the human sequence (hS100A8(43-56)) is inactive, we postulated that common hydrophobic amino acids within the S100A12 hinge sequence may be functional. The hinge domain, S100A12(38-53), was chemotactic for human monocytes and murine mast cells in vitro. S100A12(38-53) provoked an acute inflammatory response similar to that elicited by S100A12 in vivo and caused edema and leukocyte and mast cell recruitment. Circular dichroism studies showed that S100A12(38-53) had increased helical structure in hydrophobic environments. Mutations in S100A12(38-53) produced using an alanine scan confirmed that specific hydrophobic residues (I44A, I47A, and I53A) on the same face of the helix were critical for monocyte chemotaxis in vitro and generation of edema in vivo. In a hydrophobic environment such as the cell membrane, these critical residues would likely align on one face of an alpha-helix to facilitate receptor interaction. Interaction is unlikely to occur via the receptor for advanced glycation end products but, rather, via a G-protein-coupled mechanism.

The structure of the Escherichia coli nucleoside diphosphate kinase reveals a new quaternary architecture for this enzyme family

Nucleoside diphosphate kinase (NDPK) catalyzes the transfer of gamma-phosphate from nucleoside triphosphates to nucleoside diphosphates. The subunit folding and the dimeric basic structural unit are remarkably the same for available structures but, depending on species, dimers self-associate to form hexamers or tetramers. The crystal structure of the Escherichia coli NDPK reveals a new tetrameric quaternary structure for this protein family. The two tetramers differ by the relative orientation of interacting dimers, which face either the convex or the concave side of their central sheet as in either Myxococcus xanthus (type I) or E. coli (type II), respectively. In the type II tetramer, the subunits interact by a new interface harboring a zone called the Kpn loop as in hexamers, but by the opposite face of this loop. The evolutionary conservation of the interface residues indicates that this new quaternary structure seems to be the most frequent assembly mode in bacterial tetrameric NDP kinases.

Quantification of S100A12 (EN-RAGE) in Blood Varies with Sampling Method, Calcium and Heparin

S100A12 is a calcium-binding protein predominantly found in neutrophil granulocytes and monocytes. Its usefulness in monitoring inflammatory disease states depends on documentation that assay results are reliable. This study aimed at defining guidelines for blood sampling, selection of optimal material handling and reference intervals in healthy controls while taking into account the basic features of S100A12. An enzyme linked immunosorbent assay was developed based upon antibodies induced in rabbits by injection of recombinant S100A12. Our studies confirm that oligomers of S100A12 are generated in the presence of calcium. Structural changes in S100A12 mediated by calcium influence the interaction with antibody. This is proposed as the background for our very low readings of S100A12 in Ethylene Diamine Tetraacetic Acid (EDTA) plasma. Individual S100A12 levels did not change substantially over a 5-week sampling period. Based upon testing of 150 blood donors we suggest reference intervals of S100A12 in serum to be 49-1340 microg/l for women and 27-1750 microg/l for men. The estimated mean concentrations were 234 microg/l in serum samples (range 12-15791), 114 microg/l (range 3-17282) in re-calcified EDTA plasma and 48 microg/l (range 2-14843) in heparin plasma. Without adding calcium to EDTA plasma before running the assay, concentrations were around 2 microg/l (16 persons). S100A12 quantification is assumed to become relevant for diagnostic use in many disease states. The importance of the handling and analysing conditions for a reliable result was examined. We recommend serum collected in gel-containing tubes as the preferred sample material and have suggested reference intervals for healthy individuals.

Hexameric Calgranulin C (S100A12) Binds to the Receptor for Advanced Glycated End Products (RAGE) Using Symmetric Hydrophobic Target-binding Patches

Calgranulin C (S100A12) is a member of the S100 family of proteins that undergoes a conformational change upon calcium binding allowing them to interact with target molecules and initiate biological responses; one such target is the receptor for advanced glycation products (RAGE). The RAGE-calgranulin C interaction mediates a pro-inflammatory response to cellular stress and can contribute to the pathogenesis of inflammatory lesions. The soluble extracellular part of RAGE (sRAGE) was shown to decrease the inflammation response possibly by scavenging RAGE-activating ligands. Here, by using high resolution NMR spectroscopy, we identified the sRAGE-calgranulin C interaction surface. Ca2+ binding creates two symmetric hydrophobic surfaces on Ca2+-calgranulin C that allow calgranulin C to bind to the C-type immunoglobulin domain of RAGE. Apo-calgranulin C also binds to sRAGE using a completely different surface and with substantially lower affinity, thus underscoring the role of Ca2+ binding to S100 proteins as a molecular switch. By using native gel electrophoresis, chromatography, and fluorescence spectroscopy, we established that sRAGE forms tetramers that bind to hexamers of Ca2+-calgranulin C. This arrangement creates a large platform for effectively transmitting RAGE-dependent signals from extracellular S100 proteins to the cytoplasmic signaling complexes.

Olopatadine suppresses the migration of THP-1 monocytes induced by S100A12 protein

Olopatadine hydrochloride (olopatadine) is an antiallergic drug with histamine H(1) receptor antagonistic activity. Recently, olopatadine has been shown to bind to S100A12 which is a member of the S100 family of calcium-binding proteins, and exerts multiple proinflammatory activities including chemotaxis for monocytes and neutrophils. In this study, we examined the possibility that the interaction of olopatadine with S100A12 inhibits the proinflammatory effects of S100A12. Pretreatment of olopatadine with S100A12 reduced migration of THP-1, a monocyte cell line, induced by S100A12 alone, but did not affect recombinant human regulated upon activation, normal T cell expressed and secreted (RANTES)-induced migration. Amlexanox, which also binds to S100A12, inhibited the THP-1 migration induced by S100A12. However, ketotifen, another histamine H(1) receptor antagonist, had little effect on the activity of S100A12. These results suggest that olopatadine has a new mechanism of action, that is, suppression of the function of S100A12, in addition to histamine H(1) receptor antagonistic activity.

Pathologies involving the S100 proteins and RAGE

The S100 proteins are exclusively expressed in vertebrates and are the largest subgroup within the superfamily of EF-hand Ca2(+)-binding proteins Generally, S100 proteins are organized as tight homodimers (some as heterodimers). Each subunit is composed of a C-terminal, 'canonical' EF-hand, common to all EF-hand proteins, and a N-terminal, 'pseudo' EF-hand, characteristic of S100 proteins. Upon Ca2(+)-binding, the C-terminal EF-hand undergoes a large conformational change resulting in the exposure of a hydrophobic surface responsible for target binding A unique feature of this protein family is that some members are secreted from cells upon stimulation, exerting cytokine- and chemokine-like extracellular activities via the Receptor for Advanced Glycation Endproducts, RAGE. Recently, larger assemblies of some S100 proteins (hexamers, tetramers, octamers) have been also observed and are suggested to be the active extracellular species required for receptor binding and activation through receptor multimerization Most S100 genes are located in a gene cluster on human chromosome 1q21, a region frequently rearranged in human cancer The functional diversification of S100 proteins is achieved by their specific cell- and tissue-expression patterns, structural variations, different metal ion binding properties (Ca2+, Zn2+ and Cu2+) as well as their ability to form homo-, hetero- and oligomeric assemblies Here, we review the most recent developments focussing on the biological functions of the S100 proteins and we discuss the presently available S100-specific mouse models and their possible use as human disease models In addition, the S100-RAGE interaction and the activation of various cellular pathways will be discussed. Finally, the close association of S100 proteins with cardiomyopathy, cancer, inflammation and brain diseases is summarized as well as their use in diagnosis and their potential as drug targets to improve therapies in the future.