Extended Data Figure 2: Respiratory chain-powered, non-stereospecific reduction of Met-O in periplasmic proteins by the MsrPQ system maintains envelope integrity.

Upon exposure to reactive species of chlorine (RCS) and/or reactive species of oxygen (ROS), methionine residues (Met) in periplasmic proteins such as SurA and Pal get oxidized and randomly form either the R- or the S- diastereoisomer of Met-O. This results in the loss of function of some proteins important for maintaining the integrity of the envelope, such as SurA, giving rise to envelope defects. MsrP catalyses the reduction of both diastereoisomers of Met-O with the help of its molybdenum-molybdopterin (Mo-MPT) cofactor. Electrons for reduction are provided by the quinone (Q) pool of the respiratory chain through MsrQ, the inner membrane haem b-containing partner of MsrP. PG, peptidoglycan.