The Human Antimicrobial Protein Calgranulin C Participates in Control of Helicobacter pylori Growth and Regulation of Virulence

Manganese uptake by MtsABC contributes to the pathogenesis of human pathogen group A streptococcus by resisting host nutritional immune defenses

The interplay between host nutritional immune mechanisms and bacterial nutrient uptake systems has a major impact on the disease outcome. The host immune factor calprotectin (CP) limits the availability of essential transition metals, such as manganese (Mn) and zinc (Zn), to control the growth of invading pathogens. We previously demonstrated that the competition between CP and the human pathogen group A streptococcus (GAS) for Zn impacts GAS pathogenesis. However, the contribution of Mn sequestration by CP in GAS infection control and the role of GAS Mn acquisition systems in overcoming host-imposed Mn limitation remain unknown. Using a combination of in vitro and in vivo studies, we show that GAS-encoded mtsABC is a Mn uptake system that aids bacterial evasion of CP-imposed Mn scarcity and promotes GAS virulence. Mn deficiency caused by either the inactivation of mtsC or CP also impaired the protective function of GAS-encoded Mn-dependent superoxide dismutase. Our ex vivo studies using human saliva show that saliva is a Mn-scant body fluid, and Mn acquisition by MtsABC is critical for GAS survival in human saliva. Finally, animal infection studies using wild-type (WT) and CP-/- mice showed that MtsABC is critical for GAS virulence in WT mice but dispensable in mice lacking CP, indicating the direct interplay between MtsABC and CP in vivo. Together, our studies elucidate the role of the Mn import system in GAS evasion of host-imposed metal sequestration and underscore the translational potential of MtsABC as a therapeutic or prophylactic target.

Host antimicrobial peptide S100A12 disrupts the fungal membrane by direct binding and inhibits growth and biofilm formation of Fusarium species

Fungal keratitis is the foremost cause of corneal infections worldwide, of which Fusariumspp. is the common etiological agent that causes loss of vision and warrants surgical intervention. An increase in resistance to the available drugs along with severe side effects of the existing antifungals demands for new effective antimycotics. Here, we demonstrate that antimicrobial peptide S100A12 directly binds to the phospholipids of the fungal membrane, disrupts the structural integrity, and induces generation of reactive oxygen species in fungus. In addition, it inhibits biofilm formation by Fusariumspp. and exhibits antifungal property against Fusariumspp. both in vitro and in vivo. Taken together, our results delve into specific effect of S100A12 against Fusariumspp. with an aim to investigate new antifungal compounds to combat fungal keratitis.

Roles of S100A8, S100A9 and S100A12 in infection, inflammation and immunity

S100 proteins are small proteins that are only expressed in vertebrates. They are widely expressed in many different cell types and are involved in the regulation of calcium homeostasis, glucose metabolism, cell proliferation, apoptosis, inflammation and tumorigenesis. As members of the S100 protein subfamily of myeloid-related proteins, S100A8, S100A9 and S100A12 play a crucial role in resisting microbial infection and maintaining immune homeostasis. These proteins chelate the necessary metal nutrients of pathogens invading the host by means of 'nutritional immunity' and directly inhibit the growth of pathogens in the host. They interact with receptors on the cell surface to initiate inflammatory signal transduction, induce cytokine expression and participate in the inflammatory response and immune regulation. Furthermore, the increased content of these proteins during the pathological process makes them useful as disease markers for screening and detecting related diseases. This article summarizes the structure and function of the proteins S100A8, S100A9 and S100A12 and lays the foundation for further understanding their roles in infection, immunity and inflammation, as well as their potential applications in the prevention and treatment of infectious diseases.

Generation and Application of Monoclonal Antibodies against Porcine S100A8, S100A9, and S100A12 Proteins Using Hybridoma Technology

S100A8, S100A9, and S100A12 proteins are important members of the S100 protein family, act primarily as congenital immunomodulators, and are closely related to the occurrence of infectious diseases. There have been few reports on the functional properties of S100A8, S100A9, and S100A12 proteins in swine, but it is certain that porcine S100A8, S100A9, and S100A12 proteins are highly expressed in diseased swine. To address the current lack of reliable and timely detection tools for these three proteins, we generated monoclonal antibodies specific to the porcine S100A8, S100A9, and S100A12 proteins using hybridoma technology. The results of serum sample testing showed that the above monoclonal antibodies specifically recognize the proteins S100A8, S100A9, and S100A12 in the serum and were able to evaluate the content change of these proteins during the infection process. This provides the basis for the use of porcine S100A8, S100A9, and S100A12 in the surveillance and diagnosis of swine diseases and laid a foundation for further understanding their roles in infection, immunity, and inflammation, as well as their potential applications in preventing or treating gastrointestinal tract or inflammatory diseases in swine.

The functions of EF-hand proteins from host and zoonotic pathogens

EF-hand proteins not only regulate biological processes, but also influence immunity and infection. In this review, we summarize EF-hand proteins' functions in host and zoonotic pathogens, with details in structures, Ca2+ affinity, downstream targets and functional mechanisms. Studies entitled as EF-hand-related but with less solid features were also discussed. We believe it could raise cautions and facilitate proper research strategy for researchers.

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.

Multifunctional Role of S100 Protein Family in the Immune System: An Update

S100 is a broad subfamily of low-molecular weight calcium-binding proteins (9–14 kDa) with structural similarity and functional discrepancy. It is required for inflammation and cellular homeostasis, and can work extracellularly, intracellularly, or both. S100 members participate in a variety of activities in a healthy cell, including calcium storage and transport (calcium homeostasis). S100 isoforms that have previously been shown to play important roles in the immune system as alarmins (DAMPs), antimicrobial peptides, pro-inflammation stimulators, chemo-attractants, and metal scavengers during an innate immune response. Currently, during the pandemic, it was found that several members of the S100 family are implicated in the pathophysiology of COVID-19. Further, S100 family protein members were proposed to be used as a prognostic marker for COVID-19 infection identification using a nasal swab. In the present review, we compiled the vast majority of recent studies that focused on the multifunctionality of S100 proteins in the complex immune system and its associated activities. Furthermore, we shed light on the numerous molecular approaches and signaling cascades regulated by S100 proteins during immune response. In addition, we discussed the involvement of S100 protein members in abnormal defense systems during the pathogenesis of COVID-19.

Antimicrobial peptide S100A12 (calgranulin C) inhibits growth, biofilm formation, pyoverdine secretion and suppresses type VI secretion system in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen and is the major cause of corneal infections in India and worldwide. The increase in antimicrobial resistance among Pseudomonas has prompted rise in significant research to develop alternative therapeutics. Antimicrobial peptides (AMPs) are considered as potent alternatives to combat bacterial infections. In this study, we investigated the role of S100A12, a host defense peptide, against PAO1 and an ocular clinical isolate. Increased expression of S100A12 was observed in corneal tissues obtained from Pseudomonas keratitis patients by immunohistochemistry. S100A12 significantly inhibited growth of Pseudomonas in vitro as determined from colony forming units. Furthermore, recombinant S100A12 reduced the corneal opacity and the bacterial load in a mouse model of Pseudomonas keratitis. Transcriptome changes in PAO1 in response to S100A12 was investigated using RNA sequencing. The pathway analysis of transcriptome data revealed that S100A12 inhibits expression of genes involved in pyoverdine synthesis and biofilm formation. It also impedes several important pathways like redox, pyocyanin synthesis and type 6 secretion system (T6SS). The transcriptome data was further validated by checking the expression of several affected genes by quantitative PCR. Our study sheds light on how S100A12 impacts Pseudomonas and that it might have the potential to be used as therapeutic intervention in addition to antibiotics to combat infection in future.

S100A12 promotes Mn(II) binding to pneumococcal PsaA and staphylococcal MntC by Zn(II) sequestration

Human S100A12 (calgranulin C, EN-RAGE) is a Zn(II)-sequestering host-defense protein that contributes to the metal-withholding innate immune response against microbial pathogens. S100A12 coordinates Zn(II) ions at two His₃Asp sites with high affinity. A similar His₃Asp site found in calprotectin (S100A8/S100A9, calgranulin A/B), a closely related human S100 protein, can sequester divalent metal ions from the solute-binding proteins (SBPs) pneumococcal PsaA (pneumococcal surface protein A) and staphylococcal MntC (manganese transport protein C). Both SBPs are components of Mn(II) transporters and capture extracellular Mn(II) ions for subsequent delivery into the bacterial cytosol. Nevertheless, PsaA and MntC exhibit a thermodynamic preference for Zn(II) over Mn(II), and Zn(II) binding can interfere with Mn(II) acquisition. In this work, we have used a biotinylated variant of S100A12 to show that S100A12 can sequester Zn(II) ions from PsaA and MntC. Moreover, electron paramagnetic resonance (EPR) spectroscopy indicates that by sequestering Zn(II) from Zn(II)-bound PsaA and MntC, S100A12 promotes Mn(II) binding to the SBPs. These results inform the function of S100A12 in Zn(II) sequestration, and further suggest that Zn(II)-sequestering S100 proteins may inadvertently protect bacterial pathogens during infection.

The antimicrobial activity of zinc against group B Streptococcus is strain-dependent across diverse sequence types, capsular serotypes, and invasive versus colonizing isolates

BACKGROUND

Streptococcus agalactiae or Group B Streptococcus (GBS) is an encapsulated gram-positive bacterial pathobiont that commonly colonizes the lower gastrointestinal tract and reproductive tract of human hosts. This bacterium can infect the gravid reproductive tract and cause invasive infections of pregnant patients and neonates. Upon colonizing the reproductive tract, the bacterial cell is presented with numerous nutritional challenges imposed by the host. One strategy employed by the host innate immune system is intoxication of bacterial invaders with certain transition metals such as zinc.

METHODOLOGY

Previous work has demonstrated that GBS must employ elegant strategies to circumnavigate zinc stress in order to survive in the vertebrate host. We assessed 30 strains of GBS from diverse isolation sources, capsular serotypes, and sequence types for susceptibility or resistance to zinc intoxication.

RESULTS

Invasive strains, such as those isolated from early onset disease manifestations of GBS infection were significantly less susceptible to zinc toxicity than colonizing strains isolated from rectovaginal swabs of pregnant patients. Additionally, capsular type III (cpsIII) strains and the ST-17 and ST-19 strains exhibited the greatest resilience to zinc stress, whereas ST-1 and ST-12 strains as well as those possessing capsular type Ib (cpsIb) were more sensitive to zinc intoxication. Thus, this study demonstrates that the transition metal zinc possesses antimicrobial properties against a wide range of GBS strains, with isolation source, capsular serotype, and sequence type contributing to susceptibility or resistance to zinc stress.

Analysis of Susceptibility to the Antimicrobial and Anti-Biofilm Activity of Human Milk Lactoferrin in Clinical Strains of Streptococcus agalactiae With Diverse Capsular and Sequence Types

Group B Streptococcus (GBS) is one of the leading infection-related causes of adverse maternal and neonatal outcomes. This includes chorioamnionitis, which leads to preterm ruptures of membranes and can ultimately result in preterm or stillbirth. Infection can also lead to maternal and neonatal sepsis that may contribute to mortality. Currently, treatment for GBS infection include a bolus of intrapartum antibiotic prophylaxis to mothers testing positive for GBS colonization during late pregnancy. Lactoferrin is an antimicrobial peptide expressed in human breast milk, mucosal epithelia, and secondary granules of neutrophils. We previously demonstrated that lactoferrin possesses antimicrobial and antibiofilm properties against several strains of GBS. This is largely due to the ability of lactoferrin to bind and sequester iron. We expanded upon that study by assessing the effects of purified human breast milk lactoferrin against a panel of phenotypically and genetically diverse isolates of GBS. Of the 25 GBS isolates screened, lactoferrin reduced bacterial growth in 14 and biofilm formation in 21 strains. Stratifying the data, we observed that colonizing strains were more susceptible to the growth inhibition activity of lactoferrin than invasive isolates at lactoferrin concentrations between 250-750 µg/mL. Treatment with 750 µg/mL of lactoferrin resulted in differences in bacterial growth and biofilm formation between discrete sequence types. Differences in bacterial growth were also observed between capsular serotypes 1a and III. Maternally isolated strains were more susceptible to lactoferrin with respect to bacterial growth, but not biofilm formation, compared to neonatal sepsis isolates. Finally, high biofilm forming GBS strains were more impacted by lactoferrin across all isolates tested. Taken together, this study demonstrates that lactoferrin possesses antimicrobial and antibiofilm properties against a wide range of GBS isolates, with maternally isolated colonizing strains being the most susceptible.

The Innate Immune Glycoprotein Lactoferrin Represses the Helicobacter pylori cag Type IV Secretion System

Chronic infection with Helicobacter pylori increases risk of gastric diseases including gastric cancer. Despite development of a robust immune response, H. pylori persists in the gastric niche. Progression of gastric inflammation to serious disease outcomes is associated with infection with H. pylori strains which encode the cag Type IV Secretion System (cag T4SS). The cag T4SS is responsible for translocating the oncogenic protein CagA into host cells and inducing pro-inflammatory and carcinogenic signaling cascades. Our previous work demonstrated that nutrient iron modulates the activity of the T4SS and biogenesis of T4SS pili. In response to H. pylori infection, the host produces a variety of antimicrobial molecules, including the iron-binding glycoprotein, lactoferrin. Our work shows that apo-lactoferrin exerts antimicrobial activity against H. pylori under iron-limited conditions, while holo-lactoferrin enhances bacterial growth. Culturing H. pylori in the presence of holo-lactoferrin prior to co-culture with gastric epithelial cells, results in repression of the cag T4SS activity. Concomitantly, a decrease in biogenesis of cag T4SS pili at the host-pathogen interface was observed under these culture conditions by high-resolution electron microscopy analyses. Taken together, these results indicate that acquisition of alternate sources of nutrient iron plays a role in regulating the pro-inflammatory activity of a bacterial secretion system and present novel therapeutic targets for the treatment of H. pylori-related disease.

Nutritional immunity: targeting fungal zinc homeostasis

Transition metals, such as Zn²⁺, are essential dietary constituents of all biological life, including mammalian hosts and the pathogens that infect them. Therefore, to thrive and cause infection, pathogens must successfully assimilate these elements from the host milieu. Consequently, mammalian immunity has evolved to actively restrict and/or pool metals to toxic concentrations in an effort to attenuate microbial pathogenicity - a process termed nutritional immunity. Despite host-induced Zn²⁺ nutritional immunity, pathogens such as Candida albicans, are still capable of causing disease and thus must be equipped with robust Zn²⁺ sensory, uptake and detoxification machinery. This review will discuss the strategies employed by mammalian hosts to limit Zn²⁺ during infection, and the subsequent fungal interventions that counteract Zn²⁺ nutritional immunity.

The Optimization and Biological Significance of a 29-Host-Immune-mRNA Panel for the Diagnosis of Acute Infections and Sepsis

In response to the unmet need for timely accurate diagnosis and prognosis of acute infections and sepsis, host-immune-response-based tests are being developed to help clinicians make more informed decisions including prescribing antimicrobials, ordering additional diagnostics, and assigning level of care. One such test (InSep™, Inflammatix, Inc.) uses a 29-mRNA panel to determine the likelihood of bacterial infection, the separate likelihood of viral infection, and the risk of physiologic decompensation (severity of illness). The test, being implemented in a rapid point-of-care platform with a turnaround time of 30 min, enables accurate and rapid diagnostic use at the point of impact. In this report, we provide details on how the 29-biomarker signature was chosen and optimized, together with its molecular, immunological, and medical significance to better understand the pathophysiological relevance of altered gene expression in disease. We synthesize key results obtained from gene-level functional annotations, geneset-level enrichment analysis, pathway-level analysis, and gene-network-level upstream regulator analysis. Emerging findings are summarized as hallmarks on immune cell interaction, inflammatory mediators, cellular metabolism and homeostasis, immune receptors, intracellular signaling and antiviral response; and converging themes on neutrophil degranulation and activation involved in immune response, interferon, and other signaling pathways.

Antibacterial and Anti-biofilm Activity of the Human Breast Milk Glycoprotein Lactoferrin against Group B Streptococcus

Group B Streptococcus (GBS) is an encapsulated Gram-positive human pathogen that causes invasive infections in pregnant hosts and neonates, as well as immunocompromised individuals. Colonization of the human host requires the ability to adhere to mucosal surfaces and circumnavigate the nutritional challenges and antimicrobial defenses associated with the innate immune response. Biofilm formation is a critical process to facilitate GBS survival and establishment of a replicative niche in the vertebrate host. Previous work has shown that the host responds to GBS infection by producing the innate antimicrobial glycoprotein lactoferrin, which has been implicated in repressing bacterial growth and biofilm formation. Additionally, lactoferrin is highly abundant in human breast milk and could serve a protective role against invasive microbial pathogens. This study demonstrates that human breast milk lactoferrin has antimicrobial and anti-biofilm activity against GBS and inhibits its adherence to human gestational membranes. Together, these results indicate that human milk lactoferrin could be used as a prebiotic chemotherapeutic strategy to limit the impact of bacterial adherence and biofilm formation on GBS-associated disease outcomes.

A host-based two-gene model for the identification of bacterial infection in general clinical settings

OBJECTIVES

In this study, we aimed to develop a simple gene model to identify bacterial infection, which can be implemented in general clinical settings.

METHODS

We used a clinically availablereal-time quantitative polymerase chain reaction platform to conduct focused gene expression assays on clinical blood samples. Samples were collected from 2 tertiary hospitals.

RESULTS

We found that the 8 candidate genes for bacterial infection were significantly dysregulated in bacterial infection and displayed good performance in group classification, whereas the 2 genes for viral infection displayed poor performance. A two-gene model (S100A12 and CD177) displayed 93.0% sensitivity and 93.7% specificity in the modeling stage. In the independent validation stage, 87.8% sensitivity and 96.6% specificity were achieved in one set of case-control groups, and 93.6% sensitivity and 97.1% specificity in another set.

CONCLUSIONS

We have validated the signature genes for bacterial infection and developed a two-gene model to identify bacterial infection in general clinical settings.

Metal homeostasis in pathogenic Epsilonproteobacteria: mechanisms of acquisition, efflux, and regulation

Epsilonproteobacteria are a diverse class of eubacteria within the Proteobacteria phylum that includes environmental sulfur-reducing bacteria and the human pathogens, Campylobacter jejuni and Helicobacter pylori. These pathogens infect and proliferate within the gastrointestinal tracts of multiple animal hosts, including humans, and cause a variety of disease outcomes. While infection of these hosts provides nutrients for the pathogenic Epsilonproteobacteria, many hosts have evolved a variety of strategies to either sequester metals from the invading pathogen or exploit the toxicity of metals and drive their accumulation as an antimicrobial strategy. As a result, C. jejuni and H. pylori have developed mechanisms to sense changes in metal availability and regulate their physiology in order to respond to either metal limitation or accumulation. In this review, we will discuss the challenges of metal availability at the host-pathogen interface during infection with C. jejuni and H. pylori and describe what is currently known about how these organisms alter their gene expression and/or deploy bacterial virulence factors in response to these environments.

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.

Low levels of salivary metals, oral microbiome composition and dental decay

Salivary microbiome composition can change following exposure to environmental toxicants, e.g., heavy metals. We hypothesized that levels of salivary nutrients and metals would correlate with salivary microbiome composition and be associated with dental decay. Here we assess the salivary concentrations of 5 essential minerals (cobalt, copper, manganese, molybdenum, and zinc), 4 metals with some evidence of normal physiological function (chromium, nickel, tungsten, and vanadium), and 12 with known toxicity (antimony, arsenic, barium, beryllium, cadmium, cesium, lead, mercury, platinum, thallium, tin, and uranium), and their associations with salivary microbiome composition and dental decay in 61 children and adults. 16 metals were detected in 54% of participants; 8 were found in all. Marked differences in salivary bacterial taxa were associated with levels of antimony, arsenic, and mercury, after adjusting for multiple testing. Further, antimony levels were associated with the presence of decayed teeth. Thus, salivary metal levels, even at low concentrations, may impact oral health.

Group A Streptococcus AdcR Regulon Participates in Bacterial Defense against Host-Mediated Zinc Sequestration and Contributes to Virulence

Colonization by pathogenic bacteria depends on their ability to overcome host nutritional defenses and acquire nutrients. The human pathogen group A streptococcus (GAS) encounters the host defense factor calprotectin (CP) during infection. CP inhibits GAS growth in vitro by imposing zinc (Zn) limitation. However, GAS counterstrategies to combat CP-mediated Zn limitation and the in vivo relevance of CP-GAS interactions to bacterial pathogenesis remain unknown. Here, we report that GAS upregulates the AdcR regulon in response to CP-mediated Zn limitation. The AdcR regulon includes genes encoding Zn import (adcABC), Zn sparing (rpsN.2), and Zn scavenging systems (adcAII, phtD, and phtY). Each gene in the AdcR regulon contributes to GAS Zn acquisition and CP resistance. The ΔadcC and ΔrpsN.2 mutant strains were the most susceptible to CP, whereas the ΔadcA, ΔadcAII, and ΔphtD mutant strains displayed less CP sensitivity during growth in vitro However, the ΔphtY mutant strain did not display an increased CP sensitivity. The varied sensitivity of the mutant strains to CP-mediated Zn limitation suggests distinct roles for individual AdcR regulon genes in GAS Zn acquisition. GAS upregulates the AdcR regulon during necrotizing fasciitis infection in WT mice but not in S100a9-/- mice lacking CP. This suggests that CP induces Zn deficiency in the host. Finally, consistent with the in vitro results, several of the AdcR regulon genes are critical for GAS virulence in WT mice, whereas they are dispensable for virulence in S100a9-/- mice, indicating the direct competition for Zn between CP and proteins encoded by the GAS AdcR regulon during infection.

Calcium Regulates S100A12 Zinc Sequestration by Limiting Structural Variations

Antimicrobial proteins such as S100A12 and S100A8/A9 are highly expressed and secreted by neutrophils during infection and participate in human immune response by sequestering transition metals. At neutral pH, S100A12 sequesters Zn2+ with nanomolar affinity, which is further enhanced upon calcium binding. We investigated the pH dependence of human S100A12 zinc sequestration by using Co2+ as a surrogate. Apo-S100A12 exhibits strong Co2+ binding between pH 7.0 and 10.0 that progressively diminishes as the pH is decreased to 5.3. Ca2+ -S100A12 can retain nanomolar Co2+ binding up to pH 5.7. NMR spectroscopic measurements revealed that calcium binding does not alter the side-chain protonation of the Co2+ /Zn2+ binding histidine residues. Instead, the calcium-mediated modulation is achieved by restraining pH-dependent conformational changes to EF loop 1, which contains Co2+ /Zn2+ binding Asp25. This calcium-induced enhancement of Co2+ /Zn2+ binding might assist in the promotion of antimicrobial activities in humans by S100 proteins during neutrophil activation under subneutral pH conditions.

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.

Transcriptomic responses of S100 family to bacterial and viral infection in zebrafish

The S100 family proteins are a group of small acidic polypeptides and have diverse functions in regulating many aspects of physiological processes. They are structurally conserved and possess two EF-hands which are central for calcium-mediated functions. In this study, 14 S100 cDNA sequences were determined in zebrafish and their genomic organizations confirmed. Re-analyzing the gene synteny of the S100 loci identified two major S100 loci in Chr16 and Chr19 which share remarkable conservation with the S100 locus in human Chr1, suggesting they may have evolved from a single locus during the teleost specific whole genome duplication event. It appears that the homologues of human S100G and S100P have been lost in zebrafish. Expression analysis reveals that S100W, ICN1 and ICN2 are markedly expressed in embryos. Further, the transcripts of S100 genes are relatively abundant in mucosal tissues such as gills and gut. Intraperitoneal injection of poly(I:C) resulted in up-regulation of most S100 genes in the gut and spleen, with highest induction of S100V2 and S100Z detected. In fish challenged with spring viremia of carp virus (SVCV), expression of most S100 family genes was increased in the spleen between day 1 and 7 post infection, with consistent induction seen for the S100A1, S100A10b, S100B, S100ICN1, S100T, S100U, S100V1 and S100Z. Interestingly, intraperitoneal injection of Edwardsiella tarda down-regulated S100 expression in the gut but resulted in induction in the spleen. The results demonstrate that the S100 family genes are differentially modulated by bacterial and viral pathogens in zebrafish.

The novel interaction between Neisseria gonorrhoeae TdfJ and human S100A7 allows gonococci to subvert host zinc restriction

Neisseria gonorrhoeae causes the sexually-transmitted infection gonorrhea, a global disease that is difficult to treat and for which there is no vaccine. This pathogen employs an arsenal of conserved outer membrane proteins called TonB-dependent transporters (TdTs) that allow the gonococcus to overcome nutritional immunity, the host strategy of sequestering essential nutrients away from invading bacteria to handicap infectious ability. N. gonorrhoeae produces eight known TdTs, of which four are utilized for acquisition of iron or iron chelates from host-derived proteins or xenosiderophores produced by other bacteria. Of the remaining TdTs, two of them, TdfH and TdfJ, facilitate zinc uptake. TdfH was recently shown to bind Calprotectin, a member of the S100 protein family, and subsequently extract its zinc, which is then internalized by N. gonorrhoeae. Like Calprotectin, other S100s are also capable of binding transition metals such as zinc and copper, and thus have demonstrated growth suppression of numerous other pathogens via metal sequestration. Considering the functional and structural similarities of the TdTs and of the S100s, as well as the upregulation in response to Zn limitation shown by TdfH and TdfJ, we sought to evaluate whether other S100s have the ability to support gonococcal growth by means of zinc acquisition and to frame this growth in the context of the TdTs. We found that both S100A7 and S10012 are utilized by N. gonorrhoeae as a zinc source in a mechanism that depends on the zinc transport system ZnuABC. Moreover, TdfJ binds directly to S100A7, from which it internalizes zinc. This interaction is restricted to the human version of S100A7, and zinc presence in S100A7 is required to fully support gonococcal growth. These studies highlight how gonococci co-opt human nutritional immunity, by presenting a novel interaction between TdfJ and human S100A7 for overcoming host zinc restriction.

Neisseria gonorrhoeae causes the common sexually-transmitted infection gonorrhea. This bacteria’s ability to rapidly acquire antibiotic resistance factors, coupled with the lack of any effective vaccine to prevent infection, has resulted in a disease that poses a global threat and may become untreatable. A group of gonococcal outer membrane proteins called TonB-dependent transporters (TdTs) have been implicated as promising vaccine targets, as they are well-conserved and expressed across gonococcal isolates and play a vital role in allowing the pathogen to acquire essential nutrients during infection of the human host. Here, we describe the conservation and regulation of TdfJ, a gonococcal TdT whose homologues are ubiquitous in the genus Neisseria. We show that TdfJ binds directly to S100A7, a host protein that normally sequesters zinc away from invading pathogens. This novel interaction enables N. gonorrhoeae to strip S100A7 of chelated zinc for its own use. Furthermore, we show that another zinc-binding human protein, S100A12, is also utilized by N. gonorrhoeae as a zinc source by an as-yet-unidentified mechanism. This study provides insight into the functional role of the TdTs during infection and highlights these proteins as promising targets for both vaccine and antimicrobial therapy development.

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.

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.

S100 Proteins in the Innate Immune Response to Pathogens

S100 proteins are distinct dimeric EF-hand Ca²⁺-binding proteins that can bind Zn²⁺, Mn²⁺, and other transition metals with high affinity at two sites in the dimer interface. Certain S100 proteins, including S100A7, S100A12, S100A8, and S100A9, play key roles in the innate immune response to pathogens. These proteins function via a "nutritional immunity" mechanism by depleting essential transition metals in the infection that are required for the invading organism to grow and thrive. They also act as damage-associated molecular pattern ligands, which activate pattern recognition receptors (e.g., Toll-like receptor 4, RAGE) that mediate inflammation. Here we present protocols for these S100 proteins for high-level production of recombinant protein, measurement of binding affinities using isothermal titration calorimetry, and an assay of antimicrobial activity.

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.

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.

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.

S100A12 in renal and cardiovascular diseases

Expression of S100A12, a small calcium-binding protein, by neutrophils and monocytes/macrophages induces proinflammatory responses via ligation with the receptor for advanced glycation end-products (RAGE) and subsequent activation of intracellular signal transduction pathways such as the nuclear factor (NF)-κB pathway. Although S100A12 has been demonstrated to be a useful biomarker during inflammatory conditions, its precise role in the pathogenesis of renal and cardiovascular diseases has not been fully understood. Recently, several studies have employed S100A12 transgenic mice to investigate its pathological effects. Further studies using these models are required before we can translate these findings to human diseases such as renal and cardiovascular diseases.

Antimicrobial peptides as an alternative to anti-tuberculosis drugs

Tuberculosis (TB) presently accounts for high global mortality and morbidity rates, despite the introduction four decades ago of the affordable and efficient four-drugs (isoniazid, rifampicin, pyrazinamide and ethambutol). Thus, a strong need exists for new drugs with special structures and uncommon modes of action to effectively overcome M. tuberculosis. Within this scope, antimicrobial peptides (AMPs), which are small, cationic and amphipathic peptides that comprise a section of the innate immune system, are currently the leading potential agents for the treatment of TB. Many studies have recently illustrated the capability of anti-mycobacterial peptides to disrupt the normal mycobacterial cell wall function through various modes, thereby interacting with the intracellular targets, as well as encompassing nucleic acids, enzymes and organelles. This review presents a wide array of antimicrobial activities, alongside the associated properties of the AMPs that could be utilized as potential agents in therapeutic tactics for TB treatment.

Zinc'ing it out: zinc homeostasis mechanisms and their impact on the pathogenesis of human pathogen group A streptococcus

Group A Streptococccus (GAS) is a major human pathogen that causes significant morbidity and mortality. Zinc is an essential trace element required for GAS growth, however, zinc can be toxic at excess concentrations. The bacterial strategies to maintain zinc sufficiency without incurring zinc toxicity play a crucial role in host-GAS interactions and have a significant impact on GAS pathogenesis. The host deploys nutritional immune mechanisms to retard GAS growth by causing either zinc deprivation or zinc poisoning. However, GAS overcomes the zinc-dependent host defenses and survives in the hostile environment by employing complex adaptive strategies. In this review, we describe the different host immune strategies that employ either zinc limitation or zinc toxicity in different host environments to control GAS infection. We also discuss the molecular mechanisms and machineries used by GAS to evade host nutritional defenses and establish successful infection. Emerging evidence suggests that the metal transporters are major GAS virulence factors as they compete against host nutritional immune mechanisms to acquire or expel metals and promote bacterial survival in the host. Thus, identification of GAS molecules and elucidation of the mechanisms by which GAS combats host-mediated alterations in zinc availability may lead to novel interference strategies targeting GAS metal acquisition systems.

Expression of calcium-binding proteins S100A8, S100A9 and S100A12 in otitis media

OBJECTIVES

Calgranulins (calcium-binding proteins S100A8, S100A9 and S100A12) are predominant cytoplasmic proteins of neutrophils and produced by various cells, playing multiple functions in innate immunity and the inflammatory process. Although up-regulated expression of S100A8 and S100A9 genes were observed in an animal model of otitis media (OM), their expressions have not been studied in human middle ear epithelial cells in response to the OM pathogen or in patients with recurrent or chronic OM (recurrent OM/RecOM or chronic OM with effusion/COME).

STUDY DESIGN

Gene expressions were compared between Streptococcus pneumoniae (SP)-infected and non-infected human middle ear epithelial cells (HMEECs) as well as between chronic OM patients and control patients (CI).

METHODS

Gene expressions were profiled by quantitative real time PCR (qPCR). S100 proteins in OM patient and CI middle ear biopsies were detected by immunostaining.

RESULTS

S100A8, S100A9 and S100A12 gene expressions were elevated in SP-infected HMEECs in time-dependent manner. S100A8 and S100A9 but not S100A12 gene expression was significantly elevated in the middle ear mucosa of OM patients. S100A8 and S100A9 protein were observed in middle ear mucosa of OM, but not CI patients. Minimal co-localization was observed between S100A8 and S100A9 with neutrophil elastase and cytokeratin in ME sections of OM patients.

CONCLUSION

Elevated S100A8 and S100A9 gene expression in SP-infected HMEECs and in the middle ear mucosa of OM, minor co-localized with neutrophil markers suggests that middle ear epithelial cell secretion of S100A8 and S100A9 may play a role in the pathogenesis of recurrent and chronic OM.

Nickel Sequestration by the Host-Defense Protein Human Calprotectin

The human innate immune protein calprotectin (CP, S100A8/S100A9 oligomer, calgranulin A/calgranulin B oligomer, MRP-8/MRP-14 oligomer) chelates a number of first-row transition metals, including Mn(II), Fe(II), and Zn(II), and can withhold these essential nutrients from microbes. Here we elucidate the Ni(II) coordination chemistry of human CP. We present a 2.6-Å crystal structure of Ni(II)- and Ca(II)-bound CP, which reveals that CP binds Ni(II) ions at both its transition-metal-binding sites: the His3Asp motif (site 1) and the His6 motif (site 2). Further biochemical studies establish that coordination of Ni(II) at the hexahistidine site is thermodynamically preferred over Zn(II). We also demonstrate that CP can sequester Ni(II) from two human pathogens, Staphylococcus aureus and Klebsiella pneumoniae, that utilize this metal nutrient during infection, and inhibit the activity of the Ni(II)-dependent enzyme urease in bacterial cultures. In total, our findings expand the biological coordination chemistry of Ni(II)-chelating proteins in nature and provide a foundation for evaluating putative roles of CP in Ni(II) homeostasis at the host-microbe interface and beyond.

A Critical Role of Zinc Importer AdcABC in Group A Streptococcus-Host Interactions During Infection and Its Implications for Vaccine Development

Bacterial pathogens must overcome host immune mechanisms to acquire micronutrients for successful replication and infection. Streptococcus pyogenes, also known as group A streptococcus (GAS), is a human pathogen that causes a variety of clinical manifestations, and disease prevention is hampered by lack of a human GAS vaccine. Herein, we report that the mammalian host recruits calprotectin (CP) to GAS infection sites and retards bacterial growth by zinc limitation. However, a GAS-encoded zinc importer and a nuanced zinc sensor aid bacterial defense against CP-mediated growth inhibition and contribute to GAS virulence. Immunization of mice with the extracellular component of the zinc importer confers protection against systemic GAS challenge. Together, we identified a key early stage host-GAS interaction and translated that knowledge into a novel vaccine strategy against GAS infection. Furthermore, we provided evidence that a similar struggle for zinc may occur during other streptococcal infections, which raises the possibility of a broad-spectrum prophylactic strategy against multiple streptococcal pathogens.

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Host employs calprotectin to impose zinc (Zn) limitation on the human pathogen group A streptococcus (GAS) during infection.

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As a defense, GAS uses a sensor, AdcR, to monitor Zn availability, and a high-affinity transporter, AdcABC, to acquire Zn.

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Finally, we characterized the extracellular subunit of AdcA as a vaccine candidate to protect mice from GAS infections.

There is an urgent need for a human vaccine to protect against diseases caused by human pathogen, group A streptococcus (GAS). Herein, we identified the key molecular players involved in the battle between the host and invading bacteria for the critical nutrient zinc. The host recruits calprotectin at GAS infection sites to limit zinc availability to the pathogen. The pathogen senses the alterations in zinc availability using a sensor, AdcR, and outcompetes calprotectin by employing a high-affinity zinc uptake system, AdcABC. Using this knowledge, we developed a successful vaccination strategy by immunization with AdcA and demonstrated protection against GAS infections.

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.

Group B Streptococcus Induces Neutrophil Recruitment to Gestational Tissues and Elaboration of Extracellular Traps and Nutritional Immunity

Streptococcus agalactiae, or Group B Streptococcus (GBS), is a gram-positive bacterial pathogen associated with infection during pregnancy and is a major cause of morbidity and mortality in neonates. Infection of the extraplacental membranes surrounding the developing fetus, a condition known as chorioamnionitis, is characterized histopathologically by profound infiltration of polymorphonuclear cells (PMNs, neutrophils) and greatly increases the risk for preterm labor, stillbirth, or neonatal GBS infection. The advent of animal models of chorioamnionitis provides a powerful tool to study host-pathogen relationships in vivo and ex vivo. The purpose of this study was to evaluate the innate immune response elicited by GBS and evaluate how antimicrobial strategies elaborated by these innate immune cells affect bacteria. Our work using a mouse model of GBS ascending vaginal infection during pregnancy reveals that clinically isolated GBS has the capacity to invade reproductive tissues and elicit host immune responses including infiltration of PMNs within the choriodecidua and placenta during infection, mirroring the human condition. Upon interacting with GBS, murine neutrophils elaborate DNA-containing extracellular traps, which immobilize GBS and are studded with antimicrobial molecules including lactoferrin. Exposure of GBS to holo- or apo-forms of lactoferrin reveals that the iron-sequestration activity of lactoferrin represses GBS growth and viability in a dose-dependent manner. Together, these data indicate that the mouse model of ascending infection is a useful tool to recapitulate human models of GBS infection during pregnancy. Furthermore, this work reveals that neutrophil extracellular traps ensnare GBS and repress bacterial growth via deposition of antimicrobial molecules, which drive nutritional immunity via metal sequestration strategies.

An orthologue of the host-defense protein psoriasin (S100A7) is expressed in frog skin

Host-defense peptides and proteins are vital for first line protection against bacteria. Most host-defense peptides and proteins common in vertebrates have been studied primarily in mammals, while their orthologues in non-mammalian vertebrates received less attention. We found that the European Common Frog Rana temporaria expresses a protein in its skin that is evolutionarily related to the host-defense protein S100A7. This prompted us to test if the encoded protein, which is an important microbicidal protein in human skin, shows similar activity in frogs. The R. temporaria protein lacks the zinc-binding sites that are key to the antimicrobial activity of human S100A7 at neutral pH. However, despite being less potent, the R. temporaria protein does compromise bacterial membranes at low pH, similar to its human counterpart. We postulate that, while amphibian S100A7 likely serves other functions, the capacity to compromise bacterial cell membranes evolved early in tetrapod evolution.

S100A12: Friend or foe in pulmonary tuberculosis?

In humans, S100A12 (also named Calgranulin C and EN-RAGE) is mainly expressed and secreted by neutrophil granulocytes. Extracellular S100A12 is involved in innate immune responses against microorganisms and parasites. S100A12 is a ligand for the receptor for advanced glycation end products (RAGE), which is a cell surface receptor on macrophages, endothelium, and lymphocytes. In a recent study, Realegeno et al. showed that S100A12 exerts antimicrobial activity against Mycobacterium leprae in infected human macrophages. Recently, some interesting data on the antimicrobial activity of S100A12 have been reported. Proinflammatory role of S100A12 is supported by another newly found receptor, Toll-like receptor 4 (TLR4). These observations emphasize the importance of S100A12 for the development of potential therapeutic approaches to increase protective immunity or reduce immunopathogenesis.

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.

Transition Metals and Virulence in Bacteria

Transition metals are required trace elements for all forms of life. Due to their unique inorganic and redox properties, transition metals serve as cofactors for enzymes and other proteins. In bacterial pathogenesis, the vertebrate host represents a rich source of nutrient metals, and bacteria have evolved diverse metal acquisition strategies. Host metal homeostasis changes dramatically in response to bacterial infections, including production of metal sequestering proteins and the bombardment of bacteria with toxic levels of metals. In response, bacteria have evolved systems to subvert metal sequestration and toxicity. The coevolution of hosts and their bacterial pathogens in the battle for metals has uncovered emerging paradigms in social microbiology, rapid evolution, host specificity, and metal homeostasis across domains. This review focuses on recent advances and open questions in our understanding of the complex role of transition metals at the host-pathogen interface.

The Hexahistidine Motif of Host-Defense Protein Human Calprotectin Contributes to Zinc Withholding and Its Functional Versatility

Human calprotectin (CP, S100A8/S100A9 oligomer, MRP-8/MRP-14 oligomer) is an abundant host-defense protein that is involved in the metal-withholding innate immune response. CP coordinates a variety of divalent first-row transition metal ions, which is implicated in its antimicrobial function, and its ability to sequester nutrient Zn(II) ions from microbial pathogens has been recognized for over two decades. CP has two distinct transition-metal-binding sites formed at the S100A8/S100A9 dimer interface, including a histidine-rich site composed of S100A8 residues His17 and His27 and S100A9 residues His91 and His95. In this study, we report that CP binds Zn(II) at this site using a hexahistidine motif, completed by His103 and His105 of the S100A9 C-terminal tail and previously identified as the high-affinity Mn(II) and Fe(II) coordination site. Zn(II) binding at this unique site shields the S100A9 C-terminal tail from proteolytic degradation by proteinase K. X-ray absorption spectroscopy and Zn(II) competition titrations support the formation of a Zn(II)-His6 motif. Microbial growth studies indicate that the hexahistidine motif is important for preventing microbial Zn(II) acquisition from CP by the probiotic Lactobacillus plantarum and the opportunistic human pathogen Candida albicans. The Zn(II)-His6 site of CP expands the known biological coordination chemistry of Zn(II) and provides new insight into how the human innate immune system starves microbes of essential metal nutrients.

Nutrition and Helicobacter pylori: Host Diet and Nutritional Immunity Influence Bacterial Virulence and Disease Outcome

Helicobacter pylori colonizes the stomachs of greater than 50% of the world's human population making it arguably one of the most successful bacterial pathogens. Chronic H. pylori colonization results in gastritis in nearly all patients; however in a subset of people, persistent infection with H. pylori is associated with an increased risk for more severe disease outcomes including B-cell lymphoma of mucosal-associated lymphoid tissue (MALT lymphoma) and invasive adenocarcinoma. Research aimed at elucidating determinants that mediate disease progression has revealed genetic differences in both humans and H. pylori which increase the risk for developing gastric cancer. Furthermore, host diet and nutrition status have been shown to influence H. pylori-associated disease outcomes. In this review we will discuss how H. pylori is able to create a replicative niche within the hostile host environment by subverting and modifying the host-generated immune response as well as successfully competing for limited nutrients such as transition metals by deploying an arsenal of metal acquisition proteins and virulence factors. Lastly, we will discuss how micronutrient availability or alterations in the gastric microbiome may exacerbate negative disease outcomes associated with H. pylori colonization.

How host regulation of Helicobacter pylori-induced gastritis protects against peptic ulcer disease and gastric cancer

The bacterial pathogen Helicobacter pylori is the etiological agent of a range of gastrointestinal pathologies including peptic ulcer disease and the major killer, gastric adenocarcinoma. Infection with this bacterium induces a chronic inflammatory response in the gastric mucosa (gastritis). It is this gastritis that, over decades, eventually drives the development of H. pylori-associated disease in some individuals. The majority of studies investigating H. pylori pathogenesis have focused on factors that promote disease development in infected individuals. However, an estimated 85% of those infected with H. pylori remain completely asymptomatic, despite the presence of pathogenic bacteria that drive a chronic gastritis that lasts many decades. This indicates the presence of highly effective regulatory processes in the host that, in most cases, keeps a check on inflammation and protect against disease. In this minireview we discuss such known host factors and how they prevent the development of H. pylori-associated pathologies.

[Serum calgranulin C is a highly sensitive autoinflammation activity indicator in patients with familial periodic fevers]

AIM

To determine the possibility of using the serum proinflammatory calcium-binding protein, or calgranulin C (S100A12), to assess activity and therapeutic efficiency in patients with periodic disease (PD) and other familial periodic fevers (FPFs).

SUBJECTS AND METHODS

Thirty-five patients with PD and other FPDs, which were verified by molecular genetic study, were examined. In accordance with the disease activity, the patients were divided into 2 groups. The investigators determined the concentration of S100A12 by solid-phase enzyme immunoassay and that of other acute-phase inflammatory markers (erythrocyte sedimentation rate (ERT), neutrophil counts, and fibrinogen and C-reactive protein (CRP) concentrations).

RESULTS

The serum concentration of S100A12 in the stage of disease activity was 466.7 (265.22--851.7) ng/ml, which was significantly higher than in remission (244.29 (118.93--409.85) ng/ml (p=0.000002). The highest S100A12 concentrations were noted in the patients with PD; these were 758.95 (434.80--1035.95) ng/ml; the S100A12 level in the majority of PD patients even during remission remained moderately higher. An investigation of the relationship of A100A12 to genetic variants found no differences between the patients homozygous for M694V and those with other genotypes (p=0.37). Estimation of the time course of therapy-induced changes in the serum S100A12 concentration revealed its considerable reduction (р=0.0018). However, normalization of S100A12 levels was not achieved in PD. The remaining increased S100A12 concentration in these patients may be suggestive of the activity of PD despite the absence of its clinical manifestations. S100A12 as a highly sensitive marker allows more exact evaluation of the anti-inflammatory effect of therapy. The S100A12 identification of the subclinical activity of autoinflammatory diseases made all the more important since traditional inflammatory markers, such as ERT, CRP, fibrinogen, and leukocyte counts, are less sensitive for these purposes. In our study, these markers were within the reference range in remission. No differences were found in the S100A12 levels between the groups with and without amyloidosis (p=0.62).

CONCLUSION

S100A12 is a highly sensitive marker for the activity of autoinflammatory diseases and the efficiency of their therapy. The serum level of S100A12 in PD may be used to diagnose the subclinical activity of inflammation, which is of importance in monitoring the risk of amyloidosis.

Binding of transition metals to S100 proteins

The S100 proteins are a unique class of EF-hand Ca(2+) binding proteins distributed in a cell-specific, tissue-specific, and cell cycle-specific manner in humans and other vertebrates. These proteins are distinguished by their distinctive homodimeric structure, both intracellular and extracellular functions, and the ability to bind transition metals at the dimer interface. Here we summarize current knowledge of S100 protein binding of Zn(2+), Cu(2+) and Mn(2+) ions, focusing on binding affinities, conformational changes that arise from metal binding, and the roles of transition metal binding in S100 protein function.

Bacterial Strategies to Maintain Zinc Metallostasis at the Host-Pathogen Interface

Among the biologically required first row, late d-block metals from Mn^II to Zn^II, the catalytic and structural reach of Zn^II ensures that this essential micronutrient touches nearly every major metabolic process or pathway in the cell. Zn is also toxic in excess, primarily because it is a highly competitive divalent metal and will displace more weakly bound transition metals in the active sites of metalloenzymes if left unregulated. The vertebrate innate immune system uses several strategies to exploit this "Achilles heel" of microbial physiology, but bacterial evolution has responded in kind. This review highlights recent insights into transcriptional, transport, and trafficking mechanisms that pathogens use to "win the fight" over zinc and thrive in an otherwise hostile environment.