Fig. 6.
Plausible mechanism of P-cluster maturation on Av1. Assembly of P-cluster on Av1 occurs stepwise, starting with two pairs of [4Fe–4S]-like clusters, one in each αβ-dimer of Av1 (represented by Av1ΔnifH). Upon the combined action of Av2 and perhaps other unknown factors, one pair of the [4Fe–4S]-like clusters is converted to a fully assembled P-cluster (represented by Av1ΔnifZΔnifB). At this point, depending on the availability of FeMoco and the rate at which FeMoco is inserted, either the second pair of [4Fe–4S]-like clusters is converted to a P-cluster before the insertion of FeMoco (represented by Av1ΔnifB) or the FeMoco is inserted into the αβ-dimer containing the assembled P-cluster before the formation of the second P-cluster (represented by Av1ΔnifZ). In either case, maturation of the second P-cluster is assisted by the concerted action of NifZ and Av2/MgATP, as well as some other factors that may further improve the efficiency of this process.