Conservation of C4BP-binding sequence patterns in Streptococcus pyogenes M and Enn proteins

Area of Science:

• Microbiology
• Immunology
• Structural Biology

Background:

• Streptococcus pyogenes (Strep A) utilizes M proteins to recruit C4b-binding protein (C4BP), evading immune system destruction.
• The hypervariable region (HVR) of M proteins is critical for C4BP binding, with known patterns M2 and M22 implicated in vaccine design.

Purpose of the Study:

• To identify novel C4BP-binding patterns in Strep A M proteins beyond the known M2 and M22.
• To investigate the prevalence and functional significance of these patterns in M and M-like Enn proteins for vaccine development.

Main Methods:

• Determined structures of M68 and M87 HVRs complexed with C4BP fragments.
• Utilized mutagenesis to identify key amino acids for C4BP binding and refine/generate binding patterns.
• Analyzed M and Enn proteins for the presence of identified C4BP-binding patterns.

Main Results:

• Identified new C4BP-binding patterns (M68, M87) in M proteins lacking previously known motifs.
• M22 pattern was most prevalent, followed by M87, M2, and rarely M68.
• Identified C4BP-binding patterns were also present in M-like Enn proteins, confirming their binding.

Conclusions:

• C4BP-binding patterns are widespread in Strep A, found in M and/or Enn proteins across various M types.
• These prevalent patterns represent promising targets for developing effective Strep A vaccines.