Structural Insights into the Staphylococcus aureus DltC-Mediated D-Alanine Transfer

Abstract

Staphylococcus aureus (S. aureus) is a major Gram-positive pathogen, and treatment of S. aureus infections is often challenging due to widespread antibiotic resistance. In Gram-positive bacteria such as S. aureus, D-alanylation of teichoic acids (TA) reduces the net negative charge of the cell envelope and contributes to resistance to diverse antibiotics, particularly cationic antimicrobial peptides. D-alanylation is mediated by the dltABCD operon, which encodes four proteins (DltA, DltB, DltC, and DltD), all of which is essential for the multistep transfer of D-alanine to teichoic acids. Here, we present the first crystal structure of the S. aureus D-alanyl carrier protein DltC and analyze its interaction with DltA using AlphaFold3 and all-atom molecular dynamics simulations. We further show that single substitutions of SaDltA-SaDltC interface residues abolish SaDltC mediated enhancement of SaDltA catalysis. Together, these findings define a catalytically critical S. aureus DltA-DltC interface and provide a structural insight for targeting the D-alanylation pathway as a potential anti-Staphylococcus strategy.