Multi-metal Restriction by Calprotectin Impacts De Novo Flavin Biosynthesis in Acinetobacter baumannii

Abstract

Calprotectin (CP) inhibits bacterial viability through extracellular chelation of transition metals. However, how CP influences general metabolism remains largely unexplored. We show here that CP restricts bioavailable Zn and Fe to the pathogen Acinetobacter baumannii, inducing an extensive multi-metal perturbation of cellular physiology. Proteomics reveals severe metal starvation, and a strain lacking the candidate Zn^II metallochaperone ZigA possesses altered cellular abundance of multiple essential Zn-dependent enzymes and enzymes in de novo flavin biosynthesis. The ΔzigA strain exhibits decreased cellular flavin levels during metal starvation. Flavin mononucleotide provides regulation of this biosynthesis pathway, via a 3,4-dihydroxy-2-butanone 4-phosphate synthase (RibB) fusion protein, RibBX, and authentic RibB. We propose that RibBX ensures flavin sufficiency under CP-induced Fe limitation, allowing flavodoxins to substitute for Fe-ferredoxins as cell reductants. These studies elucidate adaptation to nutritional immunity and define an intersection between metallostasis and cellular metabolism in A. baumannii.

Keywords: 3,4-dihydroxy-2-butanone 4-phosphate synthase (DHBPS); Acinetobacter baumannii; antimicrobial activity; calprotectin; host-microbe interaction; nutritional immunity; riboflavin biosynthesis; transition metal homeostasis.