Cloning and sequencing of the structural gene for the small subunit of methylamine dehydrogenase from Methylobacterium extorquens AM1: evidence for two tryptophan residues involved in the active center.

In two independent clone libraries, clones were identified that hybridized with oligonucleotide probes based on N- or C-terminal polypeptide sequence of the small subunit of methylamine dehydrogenase from Methylobacterium extorquens AM1. Plasmids from all clones had in common a 5.2 kb Bam HI-HindIII DNA fragment. A 0.57 kb SacII-BclI subfragment that hybridized to the oligonucleotide probes was sequenced. Nucleotide sequence analysis coincided with polypeptide sequence data in the structural part of the small subunit with a single contradiction: amino acid 17 is Asp rather than Asn. The two amino acids that are involved in the active center which had not been determined from previous polypeptide sequencing proved to be tryptophans.