Ribosyl geometry in the transition state of Streptococcus pneumoniae methylthioadenosine nucleosidase from the 3′-²H kinetic isotope effect

Synthesis of [3′-²H]-labeled 5′-methylthioadenosine (MTA) derivatives permitted measurement of the [3′-²H] KIE of the reaction catalyzed by Streptococcus pneumoniae methylthioadenosine nucleosidase (spMTAN). The key [3′-²H] KIE revealed the partial 3′-OH polarization and H3′-endo→exo ribosyl configuration at the spMTAN transition state. A new understanding of the transition state stabilization of spMTAN-catalyzed hydrolysis is uncovered in structural features at the spMTAN transition state.