# Functional divergence of MdpS and MdpS2 reveals mucin-targeting strategies in Streptococcus oralis

## TL;DR

This study explores how two proteases in Streptococcus oralis help break down mucins, supporting bacterial adaptation in the mouth and influencing biofilm behavior.

## Contribution

The study reveals the functional divergence and complementary roles of MdpS and MdpS2 in mucin degradation and biofilm dynamics.

## Key findings

- MdpS2 selectively modulates MUC5B-rich mucus and promotes biofilm dispersal.
- MdpS and MdpS2 show overlapping but distinct mucin hydrolysis patterns.
- Both proteases are upregulated during late biofilm growth and affect mucus structure.

## Abstract

Mucin degradation is essential for understanding oral microbial adaptation, yet the enzymes involved remain incompletely understood. Herein, we have characterised two mucin-degrading proteases, MdpS and MdpS2, from the oral commensal Streptococcus oralis.

MdpS2 was characterised using physicochemical assays and substrate profiling and was compared to MdpS. Further Mdp characterisation included structural modelling, and functional assays analysing the gene expression during biofilm growth on salivary MUC5B, enzyme-induced biofilm dispersal, and mucus degradation analysed through nanoLC-MS/MS, sedimentation profiling, and microrheology.

MdpS2 shared conformational homology with MdpS despite low sequence identity and showed greater tolerance to pH and sodium chloride. Both genes were significantly upregulated during late stationary biofilm phase. MdpS and MdpS2 hydrolysed MUC5B extensively, with overlapping but distinct hydrolysis patterns. MdpS2 promoted biofilm dispersal and caused a pronounced reduction in MUC5B size and compactness. Microrheology showed selective modulation of MUC5B-rich mucus by MdpS2, while MdpS affected both MUC5B and MUC5AC networks.

MdpS and MdpS2 exhibit complementary biochemical and functional profiles, supporting their roles in mucin degradation and biofilm remodelling. These findings advance our understanding of how early colonizing streptococci may interact with mucosal surfaces, influence biofilm dynamics and oral ecology, and suggest potential applications in targeting mucus-related disorders.

•MdpS and MdpS2 are functionally complementary proteases that enable Streptococcus oralis to degrade salivary mucins.•MdpS2 selectively modulates MUC5B-rich mucus, disrupts MUC5B networks, and can promote biofilm dispersal.•These findings suggest that MdpS and MdpS2 may contribute to mucosal adaptation and biofilm remodelling, with potential applications in managing mucus-related disorders.

MdpS and MdpS2 are functionally complementary proteases that enable Streptococcus oralis to degrade salivary mucins.

MdpS2 selectively modulates MUC5B-rich mucus, disrupts MUC5B networks, and can promote biofilm dispersal.

These findings suggest that MdpS and MdpS2 may contribute to mucosal adaptation and biofilm remodelling, with potential applications in managing mucus-related disorders.