This presentation will focus on the native Fwd complex which has been purified and crystallized under anoxic atmosphere. The structure was solved using the anomalous signal from the tungsten active center. Fwd complex is composed of six different subunits FwdABCDFG organized in a Fwd(ABCDFG)2 dodecamer or Fwd(ABCDFG)4 24-meric supercomplex. FwdF subunit is the first polyferredoxin, which was structurally solved and generates interfaces in these oligomeric states. A giant electron wires of 42[4Fe-4S] clusters in Fwd(ABCDFG)4 electronically connects the four active sites. FwdB and FwdD compose a formate dehydrogenase-like module, which will use electrons from FwdF polyferredoxin. The tungstopterin cofactor, embedded between FwdB and FwdD, reduce CO2 to formate. Formate is a possible intermediate of the reaction and could be transferred from the tungstopterin active site in FwdB/FwdD to the metallohydrolase subunit FwdA via an inner cavity. The dinuclear metal center of FwdA could condense formate with the amino group of methanofuran which results in formyl-methanofuran formation.

Present structural results reinterpret the previous catalytic mechanism of the Fwd complex highlighting an unforeseen CO2 fixation system. The organization of the polyferredoxin in a giant electron network might accumulate electron to force/enhance CO2 reduction, working as a bio-capacitor.

Contact : ibs.seminaires@ibs.fr