MigC Biochemical Data (Fig 2, Fig 4, S1 Fig, S3 Fig, and S6 Fig)

To establish colonization within the host, bacterial pathogens like Acinetobacter baumannii must acquire zinc (Zn). To regulate Zn homeostasis, A. baumannii produces COG0523 family proteins, which are predicted to chaperone Zn for metalloprotein incorporation. Bioinformatic analyses identified A1S_0934 as a COG0523 protein in A. baumannii, and yeast two-hybrid screening revealed its interaction with MurD, an essential muramyl ligase. Based on this, we designated A1S_0934 as MurD-interacting GTPase COG0523 (MigC). Here, we demonstrate that MigC functions as a GTPase, with its activity enhanced upon Zn coordination via a conserved CxCC (C = Cys; x = Leu/Ile/Met) motif, forming an S3(N/O) complex. Strains lacking migC (ΔmigC) exhibit Zn depletion sensitivity and altered cell wall architecture in vitro. Biochemical and functional assays confirm that MigC interacts with MurD and inhibits its catalytic activity. CRISPRi-mediated murD knockdown reduces A. baumannii fitness and induces filamentation under Zn-limited conditions, a phenotype reversed in ΔmigC strains, indicating that MigC suppresses MurD activity in cells. Additionally, ΔmigC cells are elongated and more susceptible to ceftriaxone, consistent with compromised cell wall integrity. In a murine pneumonia model, ΔmigC exhibits reduced colonization, highlighting the significance of the MigC-MurD interaction during infection. Collectively, these findings suggest that MigC influences cell wall biogenesis, partly through MurD inhibition, underscoring the roles of MigC and MurD in A. baumannii survival and pathogenicity while broadening the functional scope of COG0523 family proteins.