# Fibrinogen‐binding M‐related proteins facilitate the recruitment of plasminogen by Streptococcus pyogenes

## TL;DR

This study shows that M-related proteins in Streptococcus pyogenes bind fibrinogen and help recruit plasminogen, which may contribute to infection and inflammation.

## Contribution

The study reveals that Mrp proteins provide an alternative mechanism for plasminogen recruitment after fibrinogen binding.

## Key findings

- Mrp proteins bind fibrinogen with nanomolar affinity via Fragment D.
- Pre-incubation with fibrinogen significantly enhances plasminogen binding by Mrp.
- Mrp are dimeric fibrillar proteins with lengths between 45.4 and 47.3 nm.

## Abstract

Group A Streptococcus (GAS) M‐related proteins (Mrp) are dimeric α‐helical coiled‐coil cell‐wall‐attached proteins. During infection, Mrp recruit human fibrinogen (Fg) to the bacterial surface, enhancing phagocytosis resistance and promoting growth in human blood. However, Mrp exhibit a high degree of sequence diversity, clustering into four evolutionarily distinct groups. It is currently unknown whether this diversity affects the host–pathogen interactions mediated by Mrp. In this study, nine Mrp sequences from the four major evolutionary groups were selected to examine the effect of sequence diversity on protein–protein interactions with Fg. Negative staining transmission electron microscopy confirmed that Mrp are fibrillar proteins measuring between 45.4 and 47.3 nm in length, and mass photometry confirmed the ability of Mrp to form dimers. Surface plasmon resonance was used to evaluate the affinity of each Mrp for Fg. All Mrp studied bound to Fg via Fragment D (FgD) with nanomolar affinity. Previous studies have linked the acquisition of plasminogen (Plg) by GAS Fg‐binding M proteins to tissue destruction and excessive stimulation of the human inflammatory response during infection. Our findings show that Mrp provide an alternative mechanism for Plg recruitment, as Plg binding by Mrp was significantly enhanced following pre‐incubation with Fg. These data suggest that Mrp play an important role in GAS host–pathogen interactions. However, further studies are necessary to investigate the relevance of these findings in vivo.