Conformational characteristics of the complete cequence of group A streptococcal M6 protein

Abstract

M protein is considered a virulence determinant on the streptococcal cell wall by virtue of its ability to allow the organism to resist attack by human neutrophils. The complete DNA sequence of the M6 gene from streptococcal strain D471 has allowed, for the first time, the study of the structural characteristics of the amino acid sequence of an entire M protein molecule. Predictive secondary structural analysis revealed that the majority of this fibrillar molecule exhibits strong alpha-helical potential and that, except for the ends, nonpolar residues in the central region of the molecule exhibit the 7-residue periodicity typical for coiled-coil proteins. Differences in this heptad pattern of nonpolar residues allow this central rod region to be divided into three subdomains which correlate essentially with the repeat regions A, B, and C/D in the M6 protein sequence. Alignment of the N-terminal half of the M6 sequence with PepM5, the N-terminal half of the M5 protein, revealed that 42% of the amino acids were identical. The majority of the identities were "core" nonpolar residues of the heptad periodicity which are necessary for the maintenance of the coiled coil. Thus, conservation of structure in a sequence-variable region of these molecules may be biologically significant. Results suggest that serologically different M proteins may be built according to a basic scheme: an extended central coiled-coil rod domain (which may vary in size among strains) flanked by functional end domains.

The Amino-Terminal Region of Drosophila MSL1 Contains Basic, Glycine-Rich, and Leucine Zipper-Like Motifs That Promote X Chromosome Binding, Self-Association, and MSL2 Binding, Respectively

“…In the case of long heptad-containing regions, trigger motifs are sometimes used in the sequence to provide a short length of highly stable coiled coil that acts as a nucleating point for subsequent coiled-coil formation (23,44). For short lengths of coiled coil, however, other features may play an important role in either stabilizing or facilitating the formation of coiled-coil structure (13). If the apolar region of MSL1 does serve as a trigger for dimerization, then the first turn of the ␣-helix would be expected to be important in zipping together the two proteins.…”

Isolation and characterization of the cell-associated region of group A streptococcal M6 protein

“…This places a small segment of the helical central rod region (residues 298 through 362) as well as the proline-and glycine-rich region (residues 363 through 416) of the M protein within the cell wall (12). Evidence peptidoglycan is L-Ala-L-Ala (13), the absence of additional alanines from the amino acid composition of the wall-associated fragment (Table 1), which would be contributed by the peptide portion of the peptidoglycan, rules out any linkage through this moiety.…”

“…Adjacent to the membrane anchor is a proline-and glycine-rich region which is likely to be located within the cell wall. The nearly regular placement of proline and giycine within the sequence suggests that this region may form a regular structure (12,16 From earlier studies, it is clear that the M protein is associated with the cell wall fraction of the streptococcal cell (9). In this study we isolated the cell wall-associated region of the M6 molecule directly from the streptococcus to determine both the region of the molecule located within the wall and the mechanism by which the molecule is attached.…”

“…From physicochemical and amino acid sequence analyses of the M5 (22), M6 (12,16), and M24 proteins (2), it is clear that M protein is composed of two alpha-helical protein chains wound around each other to form a coiled-coil structure (12,27). Although the majority of structural and immunochemical data on the M protein is derived from an amino-terminal fragment released from the streptococcus by limited pepsin digestion (2,3,(22)(23)(24)27), information regarding the Cterminal portion of this molecule is beginning to emerge (12,16,17,19,20,28).…”

“…Adjacent to the membrane anchor is a proline-and glycine-rich region which is likely to be located within the cell wall. The nearly regular placement of proline and giycine within the sequence suggests that this region may form a regular structure (12,16). This C-terminal region was found to have strong sequence homology with the so-called cell anchor region of staphylococcal protein A (5,16) and the C-terminal end of protein G, an immunoglobulin-binding protein from group G streptococci (5).…”