Figure 3

The subunits of methyl-coenzyme M reductase (Mcr). (a) The structure of Mcr (PDB ID: 1HBM) consists of two alpha, two beta, and two gamma subunits. The structure is split into two parts, each consisting of one set of subunits for clarity. The subunit alpha consists of two domains: the N-terminal domain (marine) and the C-terminal domain (dark-violet). The subunit beta also consists of two domains: the N-terminal (light-green) and the C-terminal (dark-green). The subunit gamma is shown in orange color. Two molecules of the cofactor F₄₃₀ are shown together with the substrate heterosulfide (positions indicated by arrows). The pair of split structures on the right is rotated 180 degrees around the y-axis. (b) The structures of the individual domains of the Mcr subunits shown in ribbon representation. The colors are the same as in the chart a. N-terminal domains of subunits alpha and beta, and subunit gamma originate presumably from the common origin with the ferredoxin-like fold. C-terminals of subunits alpha and beta have all-α fold. (c) left-to-right: the structure of cofactor F₄₃₀ in stick representation with the nickel atom shown as a yellow sphere; heterosulfide CoM-S-S-CoB in oxidized form; elementary functional loop with cofactor F₄₃₀ (from the subunit gamma) corresponding to the profile 604.