The crystal structure of methenyltetrahydromethanopterin cyclohydrolase from Methanobrevibacter ruminantium.

Methenyltetrahydromethanopterin cyclohydrolase (Mch) is involved in the methanogenesis pathway of archaea as a C1 unit carrier where N(5) -formyl-tetrahydromethanopterin is converted to methenyl-tetrahydromethanopterin. Mch from Methanobrevibacter ruminantium was cloned, purified, crystallized and its crystal structure solved at 1.37 Å resolution. A biologically active trimer, the enzyme is composed of two domains including an N-terminal domain of six α-helices encompassing a series of four β-sheets and a predominantly anti-parallel β-sheet at the C-terminus flanked on one side by α-helices. Sequence and structural alignments have helped identify residues involved in substrate binding and trimer formation.