The hypothesis that this relatively conserved region, corresponding to L21CE31 in M22, is part of the binding region is supported by inhibition experiments with short synthetic peptides in the M4 system [18]. to that derived from known C4BP-binding HVRs (Physique 5A). In particular, the C-terminal half is less variable than the N-terminal half and includes two dominating Leu residues and a preponderance of negatively charged residues. (B) Logo derived from 11 nonCC4BP-binding HVRs. The appearance of this logo Sivelestat sodium salt is Rabbit Polyclonal to RRAGB different from that of the logos in Figures 5A and (A). Although dominating Leu residues are seen also in this logo (most likely reflecting a coiled-coil structure), the variability is similar in both halves of the logo, and it is not clear that this C-terminal half contains a preponderance of negatively charged residues. The logos must be compared with caution, but this analysis suggests that the distribution of residues is different for those HVRs that bind C4BP and those that do not. To construct these logos, residues 1C50 of the indicated HVRs were aligned using ClustalW. The two most conserved Leu residues were used to manually align these HVRs to those analyzed in Physique 5A. Note that the logos shown here only include the 39 residues predicted to correspond to the C4BP-binding region analyzed in Physique 5A. (303 KB PDF) ppat.0020047.sg001.pdf (303K) GUID:?31143DE0-AE65-4108-BDF9-4844CFD26FA9 Abstract Many pathogenic microorganisms evade host immunity through extensive sequence variability in a protein region targeted by protective antibodies. In spite of the sequence variability, a variable region commonly retains an important ligand-binding function, reflected in the presence of a highly conserved sequence motif. Here, we analyze the limits of Sivelestat sodium salt sequence divergence in a ligand-binding region by characterizing the hypervariable region (HVR) of M protein. Our studies were focused on HVRs that bind the human match regulator C4b-binding protein (C4BP), a ligand that confers phagocytosis resistance. A previous comparison of C4BP-binding HVRs recognized residue identities that could be a part of a binding motif, but the extended analysis reported here shows that no residue identities remain when additional C4BP-binding HVRs are included. Characterization of the HVR in the M22 protein indicated that two relatively conserved Leu residues are essential for C4BP binding, but these residues are probably core residues in a coiled-coil, implying that they do not directly contribute to binding. In contrast, substitution of either of two relatively conserved Glu residues, predicted to be solvent-exposed, experienced no effect on C4BP binding, although each of these changes experienced a major effect on the antigenic properties of the HVR. Together, these findings show that HVRs of M proteins have an extraordinary capacity for sequence divergence and antigenic variability while retaining a specific ligand-binding function. Synopsis Sivelestat sodium salt Many Sivelestat sodium salt pathogens have evolved mechanisms to evade host immunity. In one such mechanism, the sequence of a surface protein varies among different strains of a pathogen. This sequence variability represents an apparent paradox, because the variable protein must retain an important function. The authors analyzed this problem in a major human pathogen. The surface-localized M protein of this bacterium varies extensively in sequence between bacterial strains, allowing immune escape. Nevertheless, the most variable part of the M protein generally binds a human plasma protein. By hijacking this human protein the bacteria evade attack by complement an important part of the innate immune system. Comparison of the ligand-binding region in different M proteins showed that these regions lack a shared amino acid sequence motif. Thus, a variable protein can retain a ligand-binding function in the absence of a conserved binding motif. Evidence is also presented that a single amino acid switch in the variable region may cause a major antigenic change, providing a selective advantage for the bacteria. Together, these data bear witness to the remarkable ability of pathogens to escape host immunity, without losing ability to cause disease. Introduction Sequence variability is usually a common feature in surface proteins of pathogenic microorganisms. Such variability may confer increased fitness because it allows the pathogen to use option receptors or allows contamination of different tissues or even different species [1C5]. However,.
The hypothesis that this relatively conserved region, corresponding to L21CE31 in M22, is part of the binding region is supported by inhibition experiments with short synthetic peptides in the M4 system [18]