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 li nking of NMN+ or NaMN+ with ATP, which in all organisms is one of the commo n step in the synthesis of the ubiquitous coenzyme NAD(+) via both de novo and salvage biosynthetic pathways. The structure of Methanobacterium thermo autotrophicum NMNATase determined using multiwavelength anomalous dispersio n phasing revealed a nucleotide-binding fold common to nucleotidyltransfera se proteins. An NAD+ molecule and a sulfate ion were bound in the active si te allowing the identification of residues involved in product binding. In addition, the role of the conserved (16)HXGH(19) active site motif in catal ysis was probed by mutagenic, enzymatic and crystallographic techniques, in cluding the characterization of an NMN+/SO42- complex of mutant H19A NMNATa se.