Detection of Iron Protein Supercomplexes in Pseudomonas aeruginosa by Native Metalloproteomics

Pseudomonas aeruginosa is a major contributor to human infections and is widely distributed in the environment. Its ability for growth under aerobic and anaerobic conditions provides adaptability to environmental changes and to confront immune responses. We applied high-throughput native 2-dimensional metalloproteomics to P. aeruginosa to examine how use of iron within the metallome responds to oxic and anoxic conditions. Metalloproteomic analyses revealed four major iron peaks, each comprised of metalloproteins with synergistic functions, including: 1) respiratory and metabolic enzymes, 2) oxidative stress response enzymes, 3) DNA synthesis and nitrogen assimilation enzymes, and 4) denitrification enzymes and related copper enzymes. Three ferritins co-eluted with the first and third iron peaks, localizing iron storage with these functions. Several metalloenzymes were more abundant at low oxygen, including alkylhydroperoxide reductase C that deactivates organic radicals produced by denitrification, all three classes of ribonucleotide reductases, ferritin (increasing in ratio relative to bacterioferritin), and denitrification enzymes. Superoxide dismutase and homogentisate 1,2-dioxygenase were more abundant at high oxygen. The co-eluting Fe peaks contained multiple iron metalloproteins of varying size, implying the presence protein supercomplexes with related functionality and co-localized iron storage. This coordination with functionality implies cellular organization at the protein complex level optimized for metal trafficking that contributes to efficient iron use and prioritization, particularly for Pseudomonas with its large genome and flexible metabolism. This study provides insight into prokaryotic metallome dynamics in response to oxygen availability and demonstrates the capabilities of native metalloproteomic methods in understanding metal use and protein-protein interactions in biological systems.