A Binuclear Cluster Supports Functional Asymmetry in Dark-Operative Protochlorophyllide Reductase

A binuclear, sulfur-bridged [Cu2S2] cluster at the NB-protein tetramer interface of DPOR enables functional asymmetry, with Cu–S and Cu–Cu distances of 2.26 and 2.62 Å.

• Why it matters: DPOR’s two identical NB-protein halves act sequentially, but how they communicate to coordinate electron transfer and substrate processing has been unknown.
• What they did: Using Cu K-edge x-ray absorption spectroscopy and cryo-EM, the study identified a sulfur-bridged dicopper cluster at the NB-protein interface, then used mutagenesis and Cu loss to test its role in activity and L-protein binding.
• The result: Cu reduction and a conserved interface cluster in three purple non-sulfur bacteria link BchB C-terminal helices; removing Cu abolishes DPOR activity and asymmetric L-protein binding without disrupting the overall fold.

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