Complete amino acid sequence of the 4Fe-4S, thermostable ferredoxin from Clostridium thermoaceticum

The complete amino acid sequence of the 4Fe-4S ferredoxin from the thermophilic bacterium Clostridium thermoaceticum has been determined. The protein is extremely thermostable and is the only known clostridial ferredoxin to contain a single [4Fe-4S] cluster. The sequence totals 63 residues and includes the first tryptophan (Trp-26) reported for a clostridial ferredoxin, and other amino acids not commonly found in clostridial or clostridial-like ferredoxins: methionine (Met-1), histidine (His-33), arginine (Arg-49), and leucine (Leu-9, -19, and -31). Sequence homology to clostridial and other 8Fe-8S ferredoxins is limited to eight to nine residues at the amino-terminal sulfhydryl grouping (Cys-10, -13, -16, and -20) and two to five residues in the carboxyterminal region. This ferredoxin is, thus, sequentially distinct from all known clostridial ferredoxins and from other bacterial ferredoxins in both the 8Fe-8S and 4Fe-4S classes.