Re-face stereospecificity of NADP dependent methylenetetrahydromethanopterin dehydrogenase from Methylobacterium extorquens AM1 as determined by NMR spectroscopy

MtdA catalyzes the dehydrogenation of N(5),N(10)-methylenetetrahydromethanopterin (methylene-H4MPT) with NADP(+) as electron acceptor. In the reaction two prochiral centers are involved, C14a of methylene-H4MPT and C4 of NADP(+), between which a hydride is transferred. The two diastereotopic protons at C14a of methylene-H4MPT and at C4 of NADPH can be seen separately in 1H-NMR spectra. This fact was used to determine the stereospecificity of the enzyme. With (14aR)-[14a-2H(1)]-[14a-13C]methylene-H4MPT as the substrate, it was found that the pro-R hydrogen of methylene-H4MPT is transferred by MtdA into the pro-R position of NADPH.