CDNA-DERIVED AMINO-ACID-SEQUENCE OF THE NADH-BINDING 51-KDA SUBUNIT OF THE BOVINE RESPIRATORY NADH DEHYDROGENASE REVEALS STRIKING SIMILARITIES TO A BACTERIAL NAD+-REDUCING HYDROGENASE

A lambda-gt10 bovine brain and a lambda-gt11 bovine heart cDNA library were screened with oligonucleotide probes corresponding to partial protein sequences directly determined from the isolated 51-kDa subunit of the bovine respiratory-chain NADH dehydrogenase. Clones were isolated that encode a protein of 464 amino acids containing all the 11 partial tryptic peptide sequences determined from the 51-kDa subunit. The size and amino acid composition of this protein agree with those determined for the purified 51-kDa subunit. Furthermore, this protein contains a putative NADH-binding domain, a possible FMN-binding site, and a putative binding site for an iron-sulfur cluster. The above evidence indicates that the cloned protein is the 51-kDa subunit or its precursor. A search for sequence similarity with proteins in the Protein Identification Resource data base has revealed that the 51-kDa subunit has 32% amino acid sequence identity with a major portion of the alpha-subunit of the soluble NAD+-reducing hydrogenase from Alcaligenes eutrophus. In particular, there are three segments of high sequence similarity (70-88%) between the two proteins which correspond to the three ligand-binding sites.