Calculating metalation in cells reveals CobW acquires CoII for vitamin B12 biosynthesis while related proteins prefer ZnII

Abstract Protein metal-occupancy (metalation) in vivo has been elusive. To address this challenge, the available free energies of metals have recently determined from responses metal sensors. Here, we use these energy values to develop a metalation-calculator which accounts for inter-metal competition and changing metal-availabilities inside cells. We calculator understand function mechanism GTPase CobW, predicted Co II -chaperone vitamin B 12 . Upon binding nucleotide (GTP) Mg , CobW assembles high-affinity site that can obtain or Zn intracellular milieu. In idealised cells with sensors at mid-points their responses, within cytosol enables outcompete CobW. Thus, is cognate metal. However, after growth different [Co ], -occupancy ranges 10 97% matches CobW-dependent synthesis. The also reveals related GTPases comparable affinities preferentially acquire due relatively weaker affinities. made here other proteins.