Identification of the active site histidine in the corrinoid protein MtrA of the energy-conserving methyltransferase complex from Methanobacterium thermoautotrophicum.

TLDR: In this article, the active site histidine residue was identified by site-directed mutagenesis to be His84 in the MtrA sequence that contains three histidines.

Abstract: The energy-conserving corrinoid-containing MtrA-H complex from Methanobacterium thermoautotrophicum is composed of eight different subunits of which MtrA harbors the corrinoid prosthetic group. EPR spectroscopic evidence has recently been presented for a histidine residue as a cobalt ligand of the cobamide [Harms, U. & Thauer, R. K. (1996a) Eur J. Biochem. 241, 149–154]. This active site histidine was now identified by site-directed mutagenesis to be His84 in the MtrA sequence that contains three histidines. This result was substantiated by sequence comparison of MtrA froin M. thermoautotrophicum, Methanococcus jannaschii, and Methanopyrus kandleri and of MtxA from Methanosarcina barkeri showing that only His84 is conserved. For comparison, the DNA sequences of the mtrEDCBAGH operon in M. kundleri and of the mtxXAH operon in M. barkeri were determined.