Structure and Function Characterization of the a1a2 Motifs of Streptococcus pyogenes M Protein in Human Plasminogen Binding

• Published in: Journal of molecular biology Vol. 431; no. 19; pp. 3804 - 3813
• Main Authors: Quek, Adam J.H., Mazzitelli, Blake A., Wu, Guojie, Leung, Eleanor W.W., Caradoc-Davies, Tom T., Lloyd, Gordon J., Jeevarajah, Devadharshini, Conroy, Paul J., Sanderson-Smith, Martina, Yuan, Yue, Ayinuola, Yetunde A., Castellino, Francis J., Whisstock, James C., Law, Ruby H.P.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 06.09.2019
• Subjects: a1a2 repeat; lysine-binding site; PAM; plasminogen kringle 2; RH motif; lysine-binding site; a1a2 repeat; RH motif; PAM; plasminogen kringle 2
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2019.07.003

Plasminogen (Plg)-binding M protein (PAM) is a group A streptococcal cell surface receptor that is crucial for bacterial virulence. Previous studies revealed that, by binding to the kringle 2 (KR2) domain of host Plg, the pathogen attains a proteolytic microenvironment on the cell surface that facilitates its dissemination from the primary infection site. Each of the PAM molecules in their dimeric assembly consists of two Plg binding motifs (called the a1 and a2 repeats). To date, the molecular interactions between the a1 repeat and KR2 have been structurally characterized, whereas the role of the a2 repeat is less well defined. Here, we report the 1.7-Å x-ray crystal structure of KR2 in complex with a monomeric PAM peptide that contains both the a1 and a2 motifs. The structure reveals how the PAM peptide forms key interactions simultaneously with two KR2 via the high-affinity lysine isosteres within the a1a2 motifs. Further studies, through combined mutagenesis and functional characterization, show that a2 is a stronger KR2 binder than a1, suggesting that these two motifs may play discrete roles in mediating the final PAM-Plg assembly. [Display omitted] •PAM is a major virulence factor of GAS and a receptor for human Plg.•PAM contains two Plg KR2 binding motifs (a1 and a2).•Co-crystal structure shows VEK75 binds to two KR2 via the a1 and a2 motifs.•Mutational studies reveal that a2 has higher affinity for Plg.•This study provides new insights into the high affinity interaction between PAM and Plg