The zinc metalloprotein MigC impacts cell wall biogenesis through interactions with an essential Mur ligase in Acinetobacter baumannii.

Abstract

To colonize and survive in the host, bacterial pathogens like Acinetobacter baumannii must acquire zinc (Zn). To maintain Zn homeostasis, A. baumannii synthesizes proteins of the COG0523 family which are predicted to chaperone Zn to metalloproteins. Bioinformatic tools identified A. baumannii A1S_0934 as a COG0523 protein, and yeast two-hybrid screening revealed that MurD, an essential muramyl ligase, interacts with A1S_0934. As such, we have named A1S_0934 MurD interacting GTPase COG0523 (MigC). Here we show that MigC is a GTPase whose activity is stimulated upon Zn coordination to a characteristic CxCC (C = Cys; x = Leu/Ile/Met) motif to form a S3(N/O) complex. MigC-deficient strains (ΔmigC) display sensitivity to Zn depletion and exhibit altered cell wall architecture in vitro. Biochemical and functional assays confirm the MigC-MurD interaction, which inhibits the catalytic activity of MurD. CRISPRi knockdowns of murD reduce A. baumannii fitness and increase filamentation during Zn depletion, a phenotype reversed in ΔmigC strains, suggesting that MigC also inhibits MurD activity in cells. ΔmigC cells are elongated and sensitized to ceftriaxone, a cephalosporin antibiotic, consistent with decreased cell wall integrity. The ΔmigC strain has reduced ability to colonize in a murine model of pneumonia highlighting the importance of the MigC-MurD interaction induced by A. baumannii infection. Together these data suggest that MigC impacts cell wall biogenesis, in part through interactions with MurD, emphasizing the importance of MigC and MurD to the survival and pathogenicity of A. baumannii while expanding the potential functions of the COG0523 family of enzymes.