Crystal structure of group A streptococcus Mac-1: insight into dimer-mediated specificity for recognition of human...

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Group A Streptococcus utilizes cysteine proteases Mac-1 and Mac-2 for immune evasion.
• These proteases target host immunoglobulin G (IgG) and Fc receptors, hindering immune responses.

Purpose of the Study:

• To determine the crystal structures of Mac-1 and its inactive mutant.
• To elucidate the structural basis of Mac-1's catalytic mechanism and dimer formation.
• To investigate the role of the dimer interface in Mac-1 function and host-pathogen interactions.

Main Methods:

• X-ray crystallography was used to obtain structures of Mac-1 and its C94A mutant.
• Site-directed mutagenesis was employed to identify key catalytic residues and analyze the dimer interface.
• IgG binding assays and enzymatic activity measurements were performed.

Main Results:

• Mac-1 adopts a papain fold, despite lacking sequence homology to other papain-like proteases.
• The enzyme forms a symmetric dimer through a unique interface, critical for IgG binding and catalytic cooperativity.
• Mutations at the dimer interface significantly reduced IgG binding and enzymatic activity.
• A distinct tunnel at the dimer interface was identified as a potential drug target.

Conclusions:

• The dimeric structure of Mac-1 is essential for its function in IgG binding and catalysis.
• The identified structural features provide insights into Mac-1 and Mac-2 functional differences.
• The Mac-1 dimer interface represents a promising target for developing novel antimicrobial agents against Group A Streptococcus.