Extended Data Fig. 5: The Elp-Hdr complex of M. marburgensis is structurally similar to the Fdh-Hdr region of the Fdh-Hdr-Fmd complex of M. hungatei.

a, Composite maps of the two different conformational states of the Elp-Hdr complex, which are very similar to the states 1 and 2 described for Fdh-Hdr-Fmd in M. hungatei¹⁸. b, The structure of the Elp-Hdr complex (left) is highly similar to the Fdh-Hdr region of the Fdh-Hdr-Fmd complex (right) of M. hungatei (PDB:7BKC). c, Atomic models of the conformational states 1 (left) and 2 (right) of the Elp-Hdr mobile arm composed of subunits ElpA (blue), B (green) and C (purple), and the N- and C-terminal domains of HdrA (khaki). Following the proposed model of electron transfer in Fdh-Hdr-Fmd¹⁸, in Elp-Hdr State 1 the [2Fe-2S] cluster of ElpC (EC) moves closer to the bifurcating FAD’ of HdrA’ (25 Å distance) to transfer two electrons through an unknown mechanism. The complex transitions to State 2 through the rotation of the mobile arm, by which the [4Fe-4S] cluster of the HdrA C terminus (HA3) moves closer to the reduced FAD’ (20 Å distance). The high-potential electron is transferred from the hydroquinone state of FAD’ to CoM-S-S-CoB via HA4’, whereas the low-potential electron from the flavosemiquinone state is transferred to HA3, the ‘shuttle cluster’. A transition back to conformational state 1 brings HA3 near enough to HA5’ for efficient electron transfer. d, ElpA (blue) is highly similar to FdhA (PDB:7BKC, orange), but lacks the molybdopterin-binding (MopB) domain and is inactive for the Fdh reaction. The AlphaFold2 model of M. hungatei FdhA (AF-Q2FRK1-F1) is also displayed (grey) to show the MopB domain, which was not deposited for M. hungatei FdhA (orange) due to low map resolution¹⁸; however, unlike for the Elp complex, clear density was observed for the MopB domain of M. hungatei FdhA. e, ElpC is highly similar to M. hungatei MvhD and shows the [2Fe-2S] cluster (EC) for electron transfer to the bifurcating FAD of HdrA.