IgA proteases of two distinct specificities are released by Neisseria meningitidis

Rabbit IgA Hinges That Resist IgA1 Protease Action Provide Options for Improved IgA-Based Therapeutic Agents

Immunoglobulin A provides a major line of defence against pathogens and plays a key role in the maintenance of the commensal microbiota in the intestinal tract. Having been shown to be more effective at tumour cell killing than IgG and strongly active against pathogens present in the mucosae, IgA antibodies have been attracting significant attention in recent years for use as therapeutic antibodies. To improve their therapeutic potential, bioengineered IgA forms with increased serum half-life and neutralizing abilities have been developed but the IgA hinge, which impacts susceptibility to bacterial proteases and ability to bridge between target and effector cells, has not yet been explored. The European rabbit has 15 IgA subclasses with exclusive hinge region motifs and varying lengths, constituting a unique model to evaluate the functional capabilities offered by incorporation of longer IgA hinges into immunoglobulins. Hinge regions from rabbit IgAs, featuring different lengths and sequences, were inserted into human IgA1 heavy chain to substitute the IgA1 hinge. These hinges did not appear to affect antigen binding nor the ability of the engineered chimeric IgA1 to bind and trigger FcαRI, as detected by IgA-mediated cell agglutination and release of superoxide by neutrophils. All rabbit hinge-human IgA1 hybrids were resistant to Clostridrum ramosum IgA protease enzyme digestion, as predicted by the lack of the cleavage site in the rabbit hinges. Some IgA1s featuring long rabbit hinges were cleaved by Neisseria meningitidis IgA1 protease cleavage type 1 or 2 enzymes, despite the lack of the predicted cleavage sites. More interestingly, the hybrid featuring the rabbit IgA15 hinge was not affected by any of the IgA proteases. The IgA15 hinge is longer than that found in human IgA1 and is composed by a unique motif with a stretch of nine consecutive Ser residues. These characteristics allow the preservation of a long hinge, with associated ability to bridge distantly spaced antigens and provide higher avidity binding, while remaining resistant to IgA protease degradation. The data suggest that the rabbit Cα15 hinge represents an interesting alternative hinge sequence for therapeutic human IgA antibodies that remains resistant to proteolytic cleavage.

The Host-Pathogen Interactions and Epicellular Lifestyle of Neisseria meningitidis

Neisseria meningitidis is a gram-negative diplococcus and a transient commensal of the human nasopharynx. It shares and competes for this niche with a number of other Neisseria species including N. lactamica, N. cinerea and N. mucosa. Unlike these other members of the genus, N. meningitidis may become invasive, crossing the epithelium of the nasopharynx and entering the bloodstream, where it rapidly proliferates causing a syndrome known as Invasive Meningococcal Disease (IMD). IMD progresses rapidly to cause septic shock and meningitis and is often fatal despite aggressive antibiotic therapy. While many of the ways in which meningococci survive in the host environment have been well studied, recent insights into the interactions between N. meningitidis and the epithelial, serum, and endothelial environments have expanded our understanding of how IMD develops. This review seeks to incorporate recent work into the established model of pathogenesis. In particular, we focus on the competition that N. meningitidis faces in the nasopharynx from other Neisseria species, and how the genetic diversity of the meningococcus contributes to the wide range of inflammatory and pathogenic potentials observed among different lineages.

The gut-meningeal immune axis: Priming brain defense against the most likely invaders

The gastrointestinal tract contains trillions of microorganisms that exist symbiotically with the host due to a tolerant, regulatory cell–rich intestinal immune system. However, this intimate relationship with the microbiome inevitably comes with risks, with intestinal organisms being the most common cause of bacteremia. The vasculature of the brain-lining meninges contains fenestrated endothelium, conferring vulnerability to invasion by circulating microbes. We propose that this has evolutionarily led to close links between gut and meningeal immunity, to prime the central nervous system defense against the most likely invaders. This paradigm is exemplified by the dural venous sinus IgA defense system, where the antibody repertoire mirrors that of the gut.

Neisseria meningitidis IgA1-specific serine protease exhibits novel cleavage activity against IgG3

Neisseria meningitidis (meningococcus) is a common bacterial colonizer of the human nasopharynx but can occasionally cause very severe systemic infections with rapid onset. Meningococci are able to degrade IgA encountered during colonization of mucosal membranes using their IgA1-specific serine protease. During systemic infection, specific IgG can induce complement-mediated lysis of the bacterium. However, meningococcal immune evasion mechanisms in thwarting IgG remain undescribed. In this study, we report for the first time that the meningococcal IgA1-specific serine protease is able to degrade IgG3 in addition to IgA. The IgG3 heavy chain is specifically cleaved in the lower hinge region thereby separating the antigen binding part from its effector binding part. Through molecular characterization, we demonstrate that meningococcal IgA1-specific serine protease of cleavage type 1 degrades both IgG3 and IgA, whereas cleavage type 2 only degrades IgA. Epidemiological analysis of 7581 clinical meningococcal isolates shows a significant higher proportion of cleavage type 1 among isolates from invasive cases compared to carrier cases, regardless of serogroup. Notably, serogroup W cc11 which is an increasing cause of invasive meningococcal disease globally harbors almost exclusively cleavage type 1 protease. Our study also shows an increasing prevalence of meningococcal isolates encoding IgA1P cleavage type 1 compared to cleavage type 2 during the observed decade (2010-2019). Altogether, our work describes a novel mechanism of IgG3 degradation by meningococci and its association to invasive meningococcal disease.

Classification, structural biology, and applications of mucin domain-targeting proteases

Epithelial surfaces throughout the body are coated by mucins, a class of proteins carrying domains characterized by a high density of O-glycosylated serine and threonine residues. The resulting mucosal layers form crucial host-microbe interfaces that prevent the translocation of microbes while also selecting for distinct bacteria via the presented glycan repertoire. The intricate interplay between mucus production and breakdown thus determines the composition of the microbiota maintained within these mucosal environments, which can have a large influence on the host during both homeostasis and disease. Most research to date on mucus breakdown has focused on glycosidases that trim glycan structures to release monosaccharides as a source of nutrients. More recent work has uncovered the existence of mucin-type O-glycosylation-dependent proteases that are secreted by pathogens, commensals, and mutualists to facilitate mucosal colonization and penetration. Additionally, immunoglobulin A (IgA) proteases promote bacterial colonization in the presence of neutralizing secretory IgA through selective cleavage of the heavily O-glycosylated hinge region. In this review, we summarize families of O-glycoproteases and IgA proteases, discuss known structural features, and review applications of these enzymes to glycobiology.

Antibody-Dependent Enhancement of Bacterial Disease: Prevalence, Mechanisms, and Treatment

Antibody-dependent enhancement (ADE) of viral disease has been demonstrated for infections caused by flaviviruses and influenza viruses; however, antibodies that enhance bacterial disease are relatively unknown. In recent years, a few studies have directly linked antibodies with exacerbation of bacterial disease. This ADE of bacterial disease has been observed in mouse models and human patients with bacterial infections. This antibody-mediated enhancement of bacterial infection is driven by various mechanisms that are disparate from those found in viral ADE. This review aims to highlight and discuss historic evidence, potential molecular mechanisms, and current therapies for ADE of bacterial infection. Based on specific case studies, we report how plasmapheresis has been successfully used in patients to ameliorate infection-related symptomatology associated with bacterial ADE. A greater understanding and appreciation of bacterial ADE of infection and disease could lead to better management of infections and inform current vaccine development efforts.

Serum IgA Fc effector functions in infectious disease and cancer

Immunoglobulin (Ig) A is the most abundant antibody isotype present at mucosal surfaces and the second most abundant in human serum. In addition to preventing pathogen entry at mucosal surfaces, IgA can control and eradicate bacterial and viral infections through a variety of antibody‐mediated innate effector cell mechanisms. The role of mucosal IgA in infection (e.g. neutralization) and in inflammatory homeostasis (e.g. allergy and autoimmunity) has been extensively investigated; by contrast, serum IgA is comparatively understudied. IgA binding to fragment crystallizable alpha receptor plays a dual role in the activation and inhibition of innate effector cell functions. Mounting evidence suggests that serum IgA induces potent effector functions against various bacterial and some viral infections including Neisseria meningitidis and rotavirus. Furthermore, in the era of immunotherapy, serum IgA provides an interesting alternative to classical IgG monoclonal antibodies to treat cancer and infectious pathogens. Here we discuss the role of serum IgA in infectious diseases with reference to bacterial and viral infections and the potential for IgA as a monoclonal antibody therapy.

Targeting of immune signalling networks by bacterial pathogens

Host defence against microbial pathogens requires appropriate coordination of multiple signalling pathways. These pathways are triggered by innate immune recognition of conserved microbial molecules, and initiate an inflammatory cascade that involves recruitment of leukocytes to the site of infection, activation of antimicrobial effector mechanisms and induction of an adaptive immune response that promotes clearance of infection and long-term immune memory. Microbial pathogens possess specialized proteins termed virulence factors, which interfere with host defence at several levels. Many virulence factors from diverse pathogens have been identified in recent years and their functions linked to disruption of essential processes of immune defence, from signalling to phagocytosis. Although the diversity of pathogens and virulence factors is immense, common themes have emerged with regard to how microbial pathogens interfere with immune responses. Here we discuss recent advances in our understanding of how virulence factors target innate and adaptive immune responses, focusing on bacterial pathogens. We also propose that pathogens responsible for causing acute infection tend to target central components (hubs) of cellular signalling pathways, causing global disruption of the host response. By contrast, pathogens that cause chronic or persistent infections tend to target more peripheral signalling network components (nodes) to promote pathogen persistence.

Active-site gating regulates substrate selectivity in a chymotrypsin-like serine protease the structure of haemophilus influenzae immunoglobulin A1 protease

We report here the first structure of a member of the immunoglobulin A protease (IgAP) family at 1.75-A resolution. This protease is a founding member of the type V (autotransporter) secretion system and is considered a virulence determinant among the bacteria expressing the enzyme. The structure of the enzyme fits that of a classic autotransporter in which several unique domains necessary for protein function are appended to a central, 100-A-long beta-helical domain. The N-terminal domain of the IgAP is found to possess a chymotrypsin-like fold. However, this catalytic domain contains a unique loop D that extends over the active site acting as a lid, gating substrate access. The data presented provide a structural basis for the known ability of IgAPs to cleave only the proline/serine/threonine-rich hinge peptide unique to IgA1 (isotype 1) in the context of the intact fold of the immunoglobulin. Based upon the structural data, as well as molecular modeling, a model suggesting that the unique extended loop D in this IgAP sterically occludes the active-site binding cleft in the absence of immunoglobulin binding is presented. Only in the context of binding of the IgA1-Fc domain in a valley formed between the N-terminal protease domain and another domain appended to the beta-helix spine (domain 2) is the lid stabilized in an open conformation. The stabilization of this open conformation through Fc association subsequently allows access of the hinge peptide to the active site, resulting in recognition and cleavage of the substrate.

Unknown functions of immunoglobulins A

Traditionally, the function of immunoglobulins A (IgA), the major type of secreted antibodies, has been thought to be restricted to binding antigens outside the epithelium basal membrane. Therefore, effector mechanisms eliminating IgA-opsonized targets have not been investigated so far. However, some indirect observations of infectious agents penetrating into tissues and blood from the environment suggest such mechanisms (analogous to IgG/IgM-dependent activation of complement and natural killers). In the present review, we examine details of IgA structure that might contribute to elucidation of IgA-dependent effector functions in human and animal immunity. Special attention is given to a putative transduction of signal about antigen binding in the active center of IgA from the Fab- to the Fc-superdomain via intramolecular conformational rearrangements. Different structure of the IgA subclasses (IgA1 and IgA2) is examined taking into account probable divergence of their functions in immune response.

Relaxed cleavage specificity of an immunoglobulin A1 protease from Neisseria meningitidis

Respiratory pathogens, such as Neisseria meningitidis, secrete site-specific proteases able to cleave human immunoglobulin A1 (IgA1), the first line of defense at mucosal membranes. Bacterial isolates show wide variability in IgA1 protease activity, and those isolated from patients with clinical infection possess the highest levels of activity. A feature of this enzyme is the self-cleavage required for secretion of the mature extracellular form. Known cleavage targets contain a proline-rich consensus recognition sequence, Pro-Pro-Ser-Pro, residing in the variable linker region that connects the protease and translocator domains. Here, we report the sequence of the NMB IgA1 protease and the unexpected self-cleavage and subsequent extracellular release of mature IgA1 protease from mutants lacking the previously defined consensus cleavage site. We investigated the possible link between enzyme secretion and variability in the linker sequence segment using site-directed mutagenesis and linker domain swapping to construct mutated and chimeric forms of the IgA1 protease from N. meningitidis strain NMB. The observed change in secreted activity levels compared to the wild-type clone indicated that the precise amino acid sequence of the intervening region, between mature IgA1 protease and the beta-core translocator domain, influences the efficacy of autoproteolytic processing. The broader specificity uncovered for the NMB IgA1 protease suggests that it could cleave a far wider range of human proteins than previously appreciated.

Protein secretion and secreted proteins in pathogenicNeisseriaceae

Secreted proteins of pathogenic bacteria are often essential virulence factors. They are involved, for example, in the adherence of the bacteria to host cells or required to suppress the host's defence mechanisms. Until recently, only IgA1 protease had been studied in detail in the NeisseriaceaeNeisseria meningitidis and Neisseria gonorrhoeae. The availability of their genome sequences, however, has boosted research in this area. Here, we present a survey of the secretome of the pathogenic Neisseriaceae, based on the available genome sequences, and the current knowledge of the functions and structures of the secreted proteins. Of the six protein-secretion pathways that are widely disseminated among Gram-negative bacteria, three pathways appear to be present among the Neisseriaceae, i.e. the autotransporter-, the two-partner- and the type I-secretion mechanisms. Comparison of the predicted secretomes reveals a considerable flexibility. As compared with N. meningitidis and the nonpathogen N. lactamica, N. gonorrhoeae appears to have a considerably degenerated secretome, which may reflect its altered niche occupancy. The flexibility of the secretome may be enhanced by the presence of ORFs in the genomes potentially encoding fragments of secreted proteins. We hypothesize that these ORFs may substitute for the corresponding fragments in the full-length genes through genetic recombination, thereby changing the host-cell receptor specificity of the secreted protein.

Effect of mutations in the human immunoglobulin A1 (IgA1) hinge on its susceptibility to cleavage by diverse bacterial IgA1 proteases

Components of the human immunoglobulin A1 (IgA1) hinge governing sensitivity to cleavage by bacterial IgA1 proteases were investigated. Recombinant antibodies with distinct hinge mutations were constructed from a hybrid comprised of human IgA2 bearing half of the human IgA1 hinge region. This hybrid antibody and all the mutant antibodies derived from it were resistant to cleavage by the IgA1 proteases from Streptococcus oralis and Streptococcus mitis biovar 1 strains but were cleaved to various degrees by those of Streptococcus pneumoniae, some Streptococcus sanguis strains, and the type 1 and 2 IgA1 proteases of Haemophilus influenzae, Neisseria meningitidis, and Neisseria gonorrhoeae. Remarkably, those proteases that cleave a Pro-Ser peptide bond in the wild-type IgA1 hinge were able to cleave mutant antibodies lacking a Pro-Ser peptide bond in the hinge, and those that cleave a Pro-Thr peptide bond in the wild-type IgA1 hinge were able to cleave mutant antibodies devoid of a Pro-Thr peptide bond in the hinge. Thus, the enzymes can cleave alternatives to their preferred postproline peptide bond when such a bond is unavailable. Peptide sequence analysis of a representative antibody digestion product confirmed this conclusion. The presence of a cleavable peptide bond near the CH2 end of the hinge appeared to result in greater cleavage than if the scissile bond was at the CH1 end of the hinge. Proline-to-serine substitution at residue 230 in a hinge containing potentially cleavable Pro-Ser and Pro-Thr peptide bonds increased the resistance of the antibody to cleavage by many IgA1 proteases.

Type V protein secretion pathway: the autotransporter story

Gram-negative bacteria possess an outer membrane layer which constrains uptake and secretion of solutes and polypeptides. To overcome this barrier, bacteria have developed several systems for protein secretion. The type V secretion pathway encompasses the autotransporter proteins, the two-partner secretion system, and the recently described type Vc or AT-2 family of proteins. Since its discovery in the late 1980s, this family of secreted proteins has expanded continuously, due largely to the advent of the genomic age, to become the largest group of secreted proteins in gram-negative bacteria. Several of these proteins play essential roles in the pathogenesis of bacterial infections and have been characterized in detail, demonstrating a diverse array of function including the ability to condense host cell actin and to modulate apoptosis. However, most of the autotransporter proteins remain to be characterized. In light of new discoveries and controversies in this research field, this review considers the autotransporter secretion process in the context of the more general field of bacterial protein translocation and exoprotein function.

Pathophysiology of meningococcal meningitis and septicaemia

Neisseria meningitidis is remarkable for the diversity of interactions that the bacterium has with the human host, ranging from asymptomatic nasopharyngeal colonisation affecting virtually all members of the population; through focal infections of the meninges, joints, or eye; to the devastating and often fatal syndrome of meningococcal septic shock and purpura fulminans.

Calciphylaxis, proteases, and purpura: an alternative hypothesis for the severe shock, rash, and hypocalcemia associated with meningococcal septicemia

The hallmarks of severe meningococcal sepsis include the rapid onset of shock, purpuric rash, and metabolic derangement, in particular, hypocalcemia. The severe ecchymoses and purpura associated with meningococcal sepsis are usually attributed to acute thrombotic episodes, attributable to the associated procoagulation disorder. An alternative explanation for the rash is a sudden extravasation of calcium from the intravascular space into the tissues. We will argue that in meningococcal sepsis, cleavage of albumin into fragments by protease(s) occurs and these fragments, along with calcium, cross the endothelium into the interstitium. The fragmentation of albumin and its loss through the endothelium would also provide a more rational explanation for the rapidity of the shock and the hypocalcemia that is so characteristic of the disease.

Invasive isolates of Neisseria meningitidis possess enhanced immunoglobulin A1 protease activity compared to colonizing strains

Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae possess the ability to cleave human IgA1 antibodies, and all successfully colonize and occasionally invade the human upper respiratory tract. N. meningitidis invades the bloodstream after a period of nasopharyngeal colonization. We directly compared levels of IgA1 protease activity in strains (n=52) derived from the cerebrospinal fluid or blood of patients with meningococcal disease with strains of N. meningitidis obtained from asymptomatic carriers (n=25). IgA1 protease activity was determined by a sensitive semiquantitative ELISA assay. Levels of IgA1 protease activity were significantly higher (P<0.0001) in strains associated with invasive meningococcal disease (98% with detectable activity, mean = 580 mU) than with those obtained from asymptomatic carriers (76% with detectable activity, mean = 280 mU). Despite marked variation in enzyme activity, almost all strains (96%) possessed the gene for IgA1 protease. Given the panmictic population structure of the bacterial isolates investigated, these data, obtained from two groups infected with N. meningitidis, but with markedly different clinical outcomes, provide the first quantitative evidence that IgA1 protease activity is a virulence determinant that contributes to the pathogenic phenotype, and suggest IgA1 protease as a potential target for prophylaxis.

Comparative characterization of the iga gene encoding IgA1 protease in Neisseria meningitidis, Neisseria gonorrhoeae and Haemophilus influenzae

Cloning and sequencing of the IgA1 protease gene (iga) from Neisseria meningitidis strain HF13 showed an overall structure equivalent to iga genes from Neisseria gonorrhoeae and Haemophilus influenzae, although no region corresponding to the gonococcal alpha-peptide was evident. An additional 18 N. meningitidis and 3 H. influenzae iga genes were amplified by the polymerase chain reaction technique and sequenced corresponding approximately to the N-terminal half of the mature enzyme. Comparative analyses of a total of 29 iga genes showed that pathogenic Neisseria have iga genes with a significantly lower degree of heterogeneity than H. influenzae iga genes. Recombinational events indicated by mosaic-like structures corresponding to those found among N. gonorrhoeae protease genes were detected among N. meningitidis iga genes. One region showed characteristic differences in sequence and length which correlated with each of the different cleavage specificities. Meningococci were extremely conserved in this region with no evidence of recombination between isolates of different cleavage specificities. Sequences further downstream showed no obvious relationship with enzyme cleavage type. This region consisted of conserved areas interspersed with highly variable areas. Amino acid sequence homologies in the variable regions of meningococci reflected the antigenic types defined by using polyclonal neutralizing antibodies.

Current status of meningococcal group B vaccine candidates: capsular or noncapsular?

Meningococcal meningitis is a severe, life-threatening infection for which no adequate vaccine exists. Current vaccines, based on the group-specific capsular polysaccharides, provide short-term protection in adults against serogroups A and C but are ineffective in infants and do not induce protection against group B strains, the predominant cause of infection in western countries, because the purified serogroup B polysaccharide fails to elicit human bactericidal antibodies. Because of the poor immunogenicity of group B capsular polysaccharide, different noncapsular antigens have been considered for inclusion in a vaccine against this serogroup: outer membrane proteins, lipooligosaccharides, iron-regulated proteins, Lip, pili, CtrA, and the immunoglobulin A proteases. Alternatively, attempts to increase the immunogenicity of the capsular polysaccharide have been made by using noncovalent complexes with outer membrane proteins, chemical modifications, and structural analogs. Here, we review the strategies employed for the development of a vaccine for Neisseria meningitidis serogroup B; the difficulties associated with the different approaches are discussed.

Immunogenicity and evolutionary variability of epitopes within IgA1 protease from serogroup A Neisseria meningitidis

Five murine epitopes were defined and mapped within IgA1 protease produced by Neisseria meningitidis. Epitopes 1 and 2 were present in IgA1 protease from all strains, and from Neisseria gonorrhoeae. Epitopes 3 through to 5 varied between subgroups of serogroup A meningococci, but have remained constant over decades within the subgroups, except for epitope 4, which changed between 1983 and 1987 during the spread of subgroup III meningococci from Asia to Africa. Binding of monoclonal antibodies to epitopes 1, 4 and 5 neutralized enzymatic function. Human sera containing antibodies to IgA1 protease as a result of natural infection inhibited binding of monoclonal antibodies to epitope 4 but not to the other epitopes.

Meningococcal lipopolysaccharides: virulence factor and potential vaccine component

Lipopolysaccharides (LPS) are surface components of the outer membrane of Neisseria meningitidis. Today, 12 different types of meningococcal LPS (immunotypes) are known, of which 3 are prevalent in the western world. The differences between these immunotypes are in the oligosaccharide part of the LPS molecule and consist of small differences in the oligosaccharide structure, the amount and location of phosphoethanolamine groups, and the degree of O acetylation of individual monosaccharides. Although the differences between the various immunotypes are small, they have a profound influence on the immunochemical and immunological properties of these molecules. Furthermore, each individual strain synthesizes a number of different LPS molecules. The expression of the various components (protective epitopes) is influenced by growth conditions and growth phase. Meningococci can endogenously sialyate their LPS, which constitutes one of the mechanisms by which N. meningitidis can evade the response of the human host. Meningococcal LPS play a key role in the induction of septic shock and can probably enhance the invasiveness of meningococcal strains and shield protective epitopes. Therefore, incorporation of (detoxified) LPS or oligosaccharide components derived therefrom might be very beneficial for the efficacy of a vaccine against group B meningococci. An overview of the development of vaccines against group B meningococci is given, and the status and potential of meningococcal LPS-derived (synthetic) oligosaccharide-protein conjugate vaccines are discussed.

Sequence-specific cleavage of protein fusions using a recombinant Neisseria type 2 IgA protease

Sequence-specific enzymatic cleavage of protein fusions is an important application in recombinant protein technology. We have used the Neisseria type 2 IgA protease (EC 3.4.24.13), produced and secreted by Escherichia coli host cells, for efficiently processing polypeptides at authentic or engineered target sites. In different substrates, the microbial protease specifically cleaves the peptide bond distal to the second Pro residue of the sequence Yaa-Pro-/-Xaa-Pro, where Yaa stands for Pro (or rarely for Pro in combination with Ala, Gly or Thr) and Xaa stands for Thr, Ser or Ala. Highly specific proteolysis has been obtained not only with soluble and purified protein fusions but also with insoluble aggregates derived from cytoplasmic inclusion bodies. The sequence-specificity and simple production of the recombinant IgA protease make it a versatile tool for the in vitro processing of recombinant proteins.

Molecular polymorphism and epidemiology of Neisseria meningitidis immunoglobulin A1 proteases

Neisseria meningitidis is one of several important bacterial pathogens that secrete a specific protease capable of cleaving human immunoglobulin A1 (IgA1) in the hinge region. To obtain further information on this putative virulence factor, we examined the IgA1 protease and iga gene region of 133 isolates of N. meningitidis assigned to 88 multilocus enzyme genotypes and representing major epidemics and carrier strains from 19 countries. Of the two IgA1 cleavage specificities previously observed, isolates associated with epidemics of meningococcal disease showed exclusively type 1 IgA1 protease activity. Considerable heterogeneity of the N. meningitidis IgA1 protease was demonstrated at both the protein and gene levels. Thus, five different forms of IgA1 protease were detected with enzyme-neutralizing antibodies raised in rabbits. An antiserum raised against a single type 2 IgA1 protease inhibited the enzyme activity of all strains examined, a finding of potential significance for the possible application of IgA1 protease in a vaccine against meningococcal disease. Examination of the iga gene region with restriction endonucleases revealed a high degree of polymorphism among strains belonging to some multilocus enzyme genotypes. The different iga gene types did not correlate with cleavage type or inhibition of the IgA1 protease. Our findings indicate that horizontal genetic exchange occurs in vivo with considerably different frequency in different clones of meningococci.

Studies on the gonococcal IgA1 protease II. Improved methods of enzyme purification and production of monoclonal antibodies to the enzyme

Two types of extremely active proteases that cleave human IgA1 are produced by pathogenic Neisseria in minute concentrations. To study the antigenicity of these enzymes, a simplified method is described to purify these enzymes from large batch cultures to obtain a sufficient quantity of these IgA1 proteases to study these characteristics. In addition, we describe the production of both rabbit polyclonal and mouse monoclonal antibodies to one of these enzymes. One such monoclonal antibody seemed directed toward the active site of the IgA1 protease and inhibited its enzymatic activity.

Proteolysis of bacterial membrane proteins by Neisseria gonorrhoeae type 2 immunoglobulin A1 protease

The immunoglobulin A1 (IgA1) proteases of Neisseria gonorrhoeae have been defined as having human IgA1 as their single permissive substrate. However, in recent years there have been reports of other proteins which are susceptible to the proteolytic activity of these enzymes. To examine the possibility that gonococcal membrane proteins are potential substrates for these enzymes, isolated outer and cytoplasmic membranes of N. gonorrhoeae were treated in vitro with exogenous pure IgA1 protease. Analysis of silver-stained sodium dodecyl sulfate-polyacrylamide gels of outer membranes indicated that there were two outer membrane proteins of 78 and 68 kDa which were cleaved by IgA1 protease in vitro in GCM 740 (a wild-type strain) and in two isogenic IgA1 protease-negative variants. Similar results were observed with a second gonococcal strain, F62, and its isogenic IgA1 protease-negative derivative. When GCM 740 cytoplasmic membranes were treated with protease, three minor proteins of 24.5, 23.5, and 21.5 kDa were cleaved. In addition, when outer membranes of Escherichia coli DH1 were treated with IgA1 protease, several proteins were hydrolyzed. While the identities of all of these proteolyzed proteins are unknown, the data presented indicate that there are several proteins found in the isolated membranes of gram-negative bacteria which are permissive in vitro substrates for gonococcal IgA1 protease.

Actions of three clostridial IgA proteases on distinct forms of immunoglobulin A molecules

Three bacterial species of Clostridium (septicum, tertium and sporogenes) were identified to produce extracellular proteases cleaving IgA to Fab and Fc fragments, as demonstrated by SDS-PAGE and immunoelectrophoretic procedures. These enzymes acted on monometric IgA1 paraproteins and normal serum IgA1 but had no activity on IgA2 paraproteins and intact secretory IgA1 from human colostrum. Their action on polyclonal serum IgA1 suggested the absence of neutralizing anti-clostridial IgA protease activity. Although the enzymes were shown not to act on secretory IgA1, they were, however, able to digest free alpha-heavy chains of the dimeric IgA molecules. Susceptibility of the alpha-heavy chain to the proteases was more likely due to the change to a more accessible conformation than because of the absence of neutralizing anti-enzymic activity.

Virulence, immunity, and vaccine related to Streptococcus pneumoniae

The pathogenesis of bacterial infection involves a series of interactions between the virulence determinants of the microorganisms and the immunity of the host. Studies on the molecular structure and immunological properties of pneumococcal virulence factors have provided general knowledge for the chemical basis of immunogenicity and prevention of bacterial infection. Antibody responses to PS and protein antigens can be greatly affected by their physicochemical properties, e.g., molecular size, specific determinants, conformation, etc. Characterization of group 19 pneumolysins and cloning of their ply genes were studied to examine the relationship of ply to virulence. Group 19 pneumococci all contained ply; the disease-isolated types of 19F and 19A appeared to show a higher specific hemolytic activity and yield than the nonpathogenic types, 19B and 19C. Genomic DNA that contained the ply gene from group 19 strains were analyzed by the polymerase chain reaction (PCR). Type 2 oligonucleotide primers recognized and initiated synthesis of an identical 1.5 kb DNA fragment in types 2, 19F, 19A, 19B, and 19C. Their sizes of restriction DNA fragments were also found to be homologous. Thus, group 19 ply genes showed remarkably similar characteristics. A difficult problem in the development of vaccines against bacterial diseases is the poor immune response of young children to purified PSs. The efficacy of pneumococcal vaccine might be improved by supplementation with inactivated pneumolysin in the form of a PS-protein conjugate.

Analysis of the immunoglobulin A protease gene of Streptococcus sanguis

The amino acid sequence T-P-P-T-P-S-P-S is tandemly duplicated in the heavy chain of human immunoglobulin A1 (IgA1), the major antibody in secretions. The bacterial pathogen Streptococcus sanguis, a precursor to dental caries and a cause of bacterial endocarditis, yields IgA protease that cleaves only the Pro-Thr peptide bond in the left duplication, while the type 2 IgA proteases of the genital pathogen Neisseria gonorrhoeae and the respiratory pathogen Haemophilus influenzae cleave only the P-T bond in the right half. We have sequenced the entire S. sanguis iga gene cloned into Escherichia coli. A segment consisting of 20 amino acids tandemly repeated 10 times, of unknown function, occurs near the amino-terminal end of the enzyme encoded in E. coli. Identification of a predicted zinc-binding region in the S. sanguis enzyme and the demonstration that mutations in this region result in production of a catalytically inactive protein support the idea that the enzyme is a metalloprotease. The N. gonorrhoeae and H. influenzae enzymes were earlier shown to be serine-type proteases, while the Bacteroides melaninogenicus IgA protease was shown to be a cysteine-type enzyme. The streptococcal IgA protease amino acid sequence has no significant homology with either of the two previously determined IgA protease sequences, that of type 2 N. gonorrhoeae and type 1 H. influenzae. The differences in both structure and mechanism among these functionally analogous enzymes underscore their role in the infectious process and offer some prospect of therapeutic intervention.

Endotoxin release from neisseria meningitidis. Relationship between key bacterial characteristics and meningococcal disease

A method was established in order to measure total and filtrable (CF) endotoxin in cultures of Neisseria meningitidis strains. The Limulus lysate (LAL) test gave results which paralleled those of the standard rabbit pyrogen test and of gas chromatography (GLC), concerning detection of different CF endotoxin levels. Meningococci varied in their ability to produce CF endotoxin. Cultures of similar bacterial densities, whether with a high (E+) or a low (E-) release of endotoxin in CF, had both high yields of endotoxin in sonicated culture suspensions determined by the LAL test. GLC demonstrated only small differences in total LPS contents between E+ and E- strains. This suggests that strains with similar cell wall endotoxin contents may vary in CF endotoxin. Electron microscopy revealed that E+ strains presented a high number of free, outer cell wall fragments (blebs, tubuli, membranes and aggregates of such structures) in surroundings. Few such free, small structures were found around E- strains. The amount of CF endotoxin of E+ strains was in part a function of the number of colony forming units (CFU/ml), and generally followed the growth curve. Because of its moment of appearance, and also based on electron microscopy findings, CF endotoxin appeared mainly to be released from living bacteria. The CF level of endotoxin was low or not detected at all in cultures of E- strains although their cultures reached higher mean CFU-levels than the niveaus required for the detection of CF endotoxin in the E+ strains. The E+ property was strain dependent. Meningococci isolated from CSF or blood had a significantly higher proportion of E+ strains (88.2%) and a higher CF endotoxin titre (greater than or equal to 10(3); 34.5%), than isolates from carriers (32.3% and 10.8%, respectively) (p less than 0.001 and p less than 0.001, respectively). A high mean CFU/ml in cultures seemed to be more often associated with isolates from patients than from carriers, more often with the presence than abscence of capsular polysaccharide (p less than 0.05), and more often with the presence than absence of the E+ property (p = 0.002). E+ strains were mostly serogroupable (i.e. encapsulated), regardless of source of the isolate (99% case and 80% carrier isolates). In contrast, serogroupable bacteria were not necessarily E+ when isolated from carriers (54.8%). The serogroup most apt to cause disease tended to have the highest proportion of E+ strains and the highest level of CF endotoxin.(ABSTRACT TRUNCATED AT 400 WORDS)

Purification, characterization, and comparison of the immunoglobulin A1 proteases of Neisseria gonorrhoeae

Each isolate of Neisseria gonorrhoeae produces one of two distinct immunoglobulin A1 (IgA1) proteases, type 1 or type 2, which are known to possess different cleavage specificities for peptide bonds in the hinge region of human IgA1. Both proteases were secreted into the culture medium throughout exponential growth; however, the activity level of the type 2 protease was 10-fold that observed for the type 1 enzyme. The type 2 protease was quite stable and resistant to a variety of inhibitors. In contrast, the type 1 enzyme was highly unstable and inhibited by low concentrations of metal chelators, salts, and thiol- or serine-specific chemical reagents. Both types of gonococcal IgA1 protease were purified from broth culture supernatants by a combination of anion-exchange, chromatofocusing, and molecular sieve chromatography techniques. The stable type 2 enzyme comprised a 114-kilodalton (kDa) peptide which converted to a still active 109-kDa peptide during isolation. In contrast, the type 1 protease possessed a 112-kDa peptide which did not convert to a smaller form and which could not be dissociated from peptides of 34 and 31 kDa without complete loss of enzyme activity.

Genetic structure of Neisseria meningitidis populations in relation to serogroup, serotype, and outer membrane protein pattern

The genetic structure of populations of Neisseria meningitidis was examined by an analysis of electrophoretically demonstrable allelic variation at 15 genes encoding enzymes in 650 isolates of eight serogroups (A, B, C, W135, X, Y, Z, and 29E) and 38 nonserogroupable isolates. A total of 331 distinctive multilocus genotypes (electrophoretic types, ETs) was identified, among which mean genetic diversity per locus (H = 0.547) was greater than in Escherichia coli and other bacterial species thus far studied. The intercontinental distribution of some ETs and the recovery of organisms of identical genotype over periods of many years strongly suggest that the genetic structure of N. meningitidis is basically clonal as a consequence of low rates of recombination of chromosomal genes. Variation among strains in serogroup, serotype, and the electrophoretic pattern of the major outer membrane proteins has little relationship to the complex structure of populations revealed by enzyme electrophoresis, which involves 14 major lineages of clones diverging from one another at genetic distances greater than 0.50. Genetic diversity among ETs of isolates of the same serogroup was, on average, 84% of that in the total sample. Clones of serogroup A were unusual in being genotypically less heterogeneous than those of other serogroups and in forming a single phylogenetic group. Isolates of the same serotype or outer membrane protein pattern were also highly heterogeneous; on average, 87 and 97%, respectively, of the total species diversity was represented by ETs of the same serotype or outer membrane protein.

Immunoglobulin A1 protease types of Neisseria gonorrhoeae and their relationship to auxotype and serovar

Immunoglobulin A1 (IgA1) proteases are extracellular bacterial proteolytic enzymes which correlate with virulence in several species of human pathogens. We report that Neisseria gonorrhoeae produced two distinct types of IgA1 protease, each of which cleaved a different peptide bond in the hinge region of human IgA1. The type of IgA1 protease produced correlated with both nutritional auxotype and outer membrane protein I serovar in this organism. Gonococcal type 1 IgA1 protease was produced primarily by N. gonorrhoeae strains which require arginine, hypoxanthine, and uracil (AHU) and which belong to the protein IA-1 or IA-2 serovar. Most isolates of other auxotypes and serovars produced type 2 IgA1 protease. Although both the AHU auxotype and protein IA serogroup were found to be associated with disseminated gonococcal infection, there was no direct correlation of IgA1 protease type with disseminated or with uncomplicated gonorrhea.

Gene structure and extracellular secretion of Neisseria gonorrhoeae IgA protease

Several human bacterial pathogens, including the Gram-negative diplococcus Neisseria gonorrhoeae, produce extracellular proteases that are specific for human immunoglobulin IgA1. Immunoglobulin A (IgA) proteases have been studied extensively and the genes of some species cloned in Escherichia coli, but their role in pathogenesis remains unclear. Recently we derived a DNA fragment of 5 kilobases (kb) from N. gonorrhoeae MS11 directing extracellular active enzyme in E. coli. Although the mature enzyme of strain MS11 was shown to have a relative molecular mass of 106,000 (Mr 106K) in gels, the DNA sequence of this cloned fragment reveals a single gene coding for a 169K precursor of IgA protease. The precursor contains three functional domains, the amino-terminal leader which is assumed to initiate the inner membrane transport of the precursor, the protease, and a carboxyl-terminal 'helper' domain apparently required for extracellular secretion (excretion). Based on the structural features of the precursor, we propose a model in which the helper serves as a pore for excretion of the protease domain through the outer membrane. IgA protease acquires an active conformation as its extracellular transport proceeds and is released as a proform from the membrane-bound helper by autoproteolysis. The soluble proform further matures into the 106 K IgA protease and a small stable alpha-protein.

[Immunoglobulin A and its significance for mucosa immunity--a contribution to the understanding of microbial interactions]

The secretory immunoglobulin A is still dominating with regard to knowledges and further investigations of the causes of mucosal immunity. Origin, formation, structure and mode of action of s-IgA are extensively explored. In the clinical range results of researches on symptoms and consequences of selective IgA deficiency are gaining importance, increasingly. Patients with IgA defect suffer up to 40 times more frequently from allergies and autoimmunopathies. In the induction of the immune response cellular components of mucosa immunity attaining the Lamina propria and the epithelium with the effector cells of Peyer's patches play a particular role.

Restriction site polymorphism in genes encoding type 2 but not type 1 gonococcal IgA1 proteases

Neisseria gonorrhoeae produces two phenotypically distinct types of IgA1 proteases, each of which cleaves a specific peptide bond in the hinge region of the human IgA1 heavy chain. The genes encoding IgA1 protease from twenty-eight different strains of N. gonorrhoeae, including twelve which produce type 1 enzyme, thirteen which produce type 2 enzyme, and three which are protease negative, were analyzed. Nine restriction site patterns were found in the iga genes. All twelve type 1 strains showed identical restriction maps of the iga gene, which differed from all the iga-2 variants. The three protease negative strains each contained DNA homologous to the probe. While strain to strain variation in restriction maps of specific genes is not unique and has been reported in N. gonorrhoeae previously, the existence of such restriction site polymorphism among iga-2 genes contrasts strongly with the lack of such variation among iga-1 genes. The basis for this lack of diversity among the iga-1 genes is under further investigation.

The site of cleavage in human alpha chains of IgA1 and IgA2:A2m(1) allotype paraproteins by the clostridial IGA protease

Fc fragments of human immunoglobulin A(IgA) of IgA1 subclass and IgA2 subclass of A2m(1) allotype were prepared from IgA paraproteins by digestion with a protease from Clostridium sp. (M.O.-6). The N-terminal tetrapeptide of Val-Pro-Ser-Thr- for the Fc of IgA1 subclass, and that of Val-Pro-Pro-Pro- for the Fc of IgA2:A2m(1) allotype, were identified by sequence analysis. The site of cleavage by the protease was defined to be at the Pro-Val peptide bond, which is a common peptide bond present at 221-222 in both alpha chains. IgA of IgA2 subclass of A2m(2) allotype is resistant to the protease due to the different, Arg-Val, peptide bond at the same position.

IgA1 protease cleaves heavy chains independently in dimeric human IgA1

Bacterial IgA1 proteases have substrate specificity for human IgA1 immunoglobulin, and cleave both the heavy (alpha) chains where they are paired by disulfide bonds in the hinge region. To determine if the close apposition of the alpha chains allows a single enzyme-substrate-binding event to cleave both hinge region peptides we quantitated the relative levels of intermediate products during the course of complete hydrolysis of an IgA1 paraprotein. The substrate had four Fab regions, analogous to a secretory IgA dimer. The experimental data were then compared to computer-generated models in which various levels of cooperativity among Fab regions were tested. The results most closely conformed to a model in which each individual alpha chain is proteolyzed independently, without regard to the total number of hinge region peptides available in the substrate IgA1. These results will be used to guide the design of IgA1 hinge region peptide analogues as IgA1 protease inhibitors.

Neisseria meningitidis

N. meningitidis continues to be a worldwide cause of human disease, usually in otherwise healthy individuals. The natural habitat and reservoir for meningococci are the mucosal surfaces of the human nasopharynx and to a lesser extent, the urogenital tract and anal canal. In most instances meningococcal colonization of mucosal surfaces is asymptomatic but may produce local infection. In those individuals who lack serum bactericidal activity against the meningococcus, colonization of mucosal surfaces and bloodstream invasion by N. meningitidis can lead to devastating meningitis and septicemia. Recent studies on the ultrastructure of the meningococcus and on the mechanisms of pathogenesis have given us new insight into meningococcal infections and suggest ways for improved immunoprophylaxis. Currently, penicillin is the drug of choice for the treatment of meningococcal meningitis and septicemia. However, the report of meningococci with antibiotic resistant plasmids is alarming and in the future may alter traditional treatment regimens.

Purification and characterization of an immunoglobulin A1 protease from Bacteroides melaninogenicus

Attention has recently been focused on bacterial proteases with the capacity to cleave immunoglobulin A (IgA proteases) as possible pathogenic factors in bacterial meningitis, gonorrhoea, and destructive periodontal disease. Here, we describe a method for the rapid purification of a specific IgA1 protease from Bacteroides melaninogenicus. The IgA1 protease was purified 6,172-fold with a yield of 9% by ammonium sulfate precipitation, DEAE-ion exchange chromatography, and separation on a preparative TSK-G 3000SWG high-pressure gel permeation chromatography column. The enzyme was specific for human IgA1 and cleaved a prolyl-seryl peptide bond in the hinge region of the alpha 1 chain between residues 223 and 224. The molecular weight of the enzyme was 62,000, the isoelectric point was 5.0, and the Km was 3.4 X 10(-6). The enzyme was active over a broad pH range and had maximal activity at pH 5.0. B. melaninogenicus IgA1 protease was classified as a thiol protease on the basis of its inhibition by traditional protease inhibitors and the fact that it was active only under reducing conditions.

Nucleotide sequence homology between the immunoglobulin A1 protease genes of Neisseria gonorrhoeae, Neisseria meningitidis, and Haemophilus influenzae

Isolated DNA fragments encoding the immunoglobulin A1 (IgA1) protease of Neisseria gonorrhoeae were used as hybridization probes to search for homologous sequences in whole cell DNA from Neisseria meningitidis and Haemophilus influenzae. Significant homology was detected. That the detected homology represented IgA1 protease-specific sequences was confirmed by the cloning of these sequences in Escherichia coli HB101 and demonstrating the expression of IgA1 protease by these transformed cells. Molecular probing of commensal Neisseria and Haemophilus species, which do not elaborate IgA1 protease activity, revealed that they were devoid of sequence homology with the cloned IgA1 protease gene DNA.

Immunoglobulin A proteases in gram-negative bacteria isolated from human urinary tract infections

Several strains of gram-negative bacteria (seven genera, eight species) isolated from patients with urinary tract infections were found to hydrolyze myeloma immunoglobulin A (IgA) protein. Human IgG and IgM and colostrum IgA were not degraded by these organisms. Examination of cleavage digests showed two fragments of different electrophoretic mobilities, with antigenic reactivity and sodium dodecyl sulfate polyacrylamide gel electrophoresis profiles consistent with their identification as Fc and Fab components. The immunoelectrophoresis patterns of cleavage digests suggested that the proteases responsible for this hydrolysis may be dissimilar in the specificity of their IgA cleavage sites.

Antigenic heterogeneity of immunoglobulin A1 proteases from encapsulated and non-encapsulated Haemophilus influenzae

Indirect evidence suggests that immunoglobulin A1 (IgA1) proteases may be factors in the pathogenesis of certain infectious diseases, including meningitis, gonorrhoea, and destructive periodontitis. Bacterial IgA1 proteases are therefore potential candidates as vaccines. In this study, IgA1 proteases from 166 clinical isolates and reference strains of Haemophilus influenzae and Haemophilus aegyptius were compared with regard to specific activity and pattern of enzyme inhibition by antisera raised against IgA1 protease from nine selected strains of H. influenzae. A total of 93% of H. influenzae strains and all H. aegyptius strains had detectable IgA1 protease activity. The majority of strains cleaved a prolyl-seryl or a prolyl-threonyl peptide bond in the alpha 1 hinge region, whereas occasional H. influenzae strains possessed two separate IgA1 proteases with these two specific activities. Of the 155 IgA1 protease-producing strains, all except 12 could be assigned to one of 14 IgA1 protease "inhibition types," each defined by a characteristic pattern of inhibition by the nine antisera. There was no correlation between IgA1 protease type and biotype of the strains. However, among 92 encapsulated H. influenzae strains, a close correlation between capsular serotype and IgA1 protease type was observed. With the exception of serotype f, strains of all capsular serotypes produced an exclusive antigenic type of IgA1 protease. All 38 strains of serotype b produced IgA1 protease of inhibition type 1, which was never demonstrated in non-encapsulated H. influenzae strains. These results facilitate the detection of an antibody response against specific IgA1 proteases and are of practical value for a possible future vaccine against H. influenzae serotype b infections.

Inhibition of microbial IgA proteases by human secretory IgA and serum

Microbial IgA proteases cleave human serum IgA1 immunoglobulin, but human secretory IgA is resistant to hydrolysis. We have found this resistance to be due to an inhibition of protease activity that is mediated by the Fab region of secretory IgA. The IgA proteases of the genus Neisseria are more sensitive to inhibition than is the protease of Streptococcus sanguis. There is also a serum inhibitor of Neisseria proteases that co-chromatographs with IgG. Monoclonal (myeloma) human IgG proteins and plasma protease inhibitors such as alpha-1-antitrypsin and alpha-2-macroglobulin do not inhibit. Human sera do not contain inhibitor to S. sanguis protease activity. We conclude that microbial IgA proteases are subject to inhibition by IgA in secretions and IgG in serum, and this activity is most consistent with being an anti-enzyme antibody. The insensitivity of S. sanguis IgA protease to inhibition is unexplained but provides further evidence that the IgA proteases are structurally diverse.

Allotypic and isotypic aspects of human immunoglobulin A

The location of isotypic, isoallotypic and allotypic determinants is reviewed in the light of data obtained when specific antisera are tested with proteolytic fragments of IgA molecules or mutants of IgA obtained from patients with alpha-heavy chain disease. Isotypic determinants are distributed throughout the alpha chain constant regions although when intact IgA proteins are used as immunogens the CH3 domain is immunodominant. Alpha 1 subclass specific isotypic determinants are present in both Fab and Fc fragments. Amino acid sequence analysis suggest that alpha 1 subclass isotypic determinants depend on substitution in the CH1, hinge and/or CH2 domain. The isoallotypic determinants nA2m(2) appears to be located on the CH1 domain and appears to require disulphide-linked alpha chains for its expression. The allotypic determinant A2m(2) appears to be located in the CH3 domain involving residues 428, 458 and/or 467. The latter residues are present in both A2m(1) and A1 proteins which indicates that for A2m(1) to be the antithetical determinant of A2m(2), the determinant formed by residues 428, 458 and/or 467 in these proteins must be influenced by subclass differences which allows its expression in A2m(1) proteins and not in A1 proteins.

Molecular biology of Haemophilus influenzae IgA1 proteases

IgA1 proteases of two distinct specificities were demonstrated among 95 isolates of Haemophilus influenzae and nine isolates of H. aegyptius. The two enzymes cleaved two different peptide bonds in the hinge region of the alpha chain of IgA1: a prolyl-seryl bond located at position 231-232 (type A cleavage) and a prolyl-threonyl peptide bond between residues 235 and 236 (type B cleavage). Each strain of H. influenzae produced either one or both of these types of enzymes, whereas all H. aegyptius strains produced type A enzyme only. The application of enzyme-neutralizing antibodies to the study of IgA1 proteases produced by the 104 strains of H. influenzae and H. aegyptius revealed at least 15 different types of protease activities based on inhibition patterns in nine selected antibody preparations. The types of IgA1 proteases closely correlated with the serotype of encapsulated strains of H. influenzae. The study suggests that H. influenzae strains produce at least two serologically different IgA1 proteases with distinct or identical enzymatic activities.