Insights into ligand binding and catalysis of a central step in NAD+ synthesis: structures of Methanobacterium thermoautotrophicum NMN adenylyltransferase complexes.

Nicotinamide mononucleotide adenylyltransferase (NMNATase) catalyzes the linking of NMN(+) or NaMN(+) with ATP, which in all organisms is one of the common step in the synthesis of the ubiquitous coenzyme NAD(+), via both de novo and salvage biosynthetic pathways. The structure of Methanobacterium thermoautotrophicum NMNATase determined using multiwavelength anomalous dispersion phasing revealed a nucleotide-binding fold common to nucleotidyltransferase proteins. An NAD(+) molecule and a sulfate ion were bound in the active site allowing the identification of residues involved in product binding. In addition, the role of the conserved (16)HXGH(19) active site motif in catalysis was probed by mutagenic, enzymatic and crystallographic techniques, including the characterization of an NMN(+)/SO4(2-) complex of mutant H19A NMNATase.