Correlation of x-ray deduced and experimental amino acid sequences of trimethylamine dehydrogenase

The amino acid sequence of the iron-sulfur-flavoprotein, trimethylamine dehydrogenase, isolated from the bacterium W3A1 has been deduced from the x-ray diffraction pattern obtained at 2.4-A resolution. This sequence has been compared to portions of the primary sequence derived by gas-phase sequencing of isolated peptides obtained from cyanogen bromide and endoprotease Arg-C and Asp-N digestions of the purified enzyme. A consensus sequence has resulted and is comprised of 729 amino acids with Ala at both NH2- and COOH-terminal positions. The consensus sequence contains 13 cysteine residues. Approximately 80% of the sequence has been confirmed by direct sequencing with approximately 81% agreement with the x-ray deduced sequence. The calculated subunit molecular mass of the apoenzyme is 78,899 Da, in good agreement with published values of approximately 83,000. The anomalous scattering map from the native protein has also been shown to provide accurate information about the positions of most of the weak anomalous scattering centers such as sulfur or phosphorus atoms and to complement x-ray or chemical sequencing methods.