Insights into Ligand Binding and Catalysis of a Central Step in NAD super(+) Synthesis. Structures of Methanobacterium thermoautotrophicum NMN Adenylyltransferase Complexes

Nicotinamide mononucleotide adenylyltransferase (NMNATase) catalyzes the linking of NMN super(+) or NaMN super(+) with ATP, which in all organisms is one of the common step in the synthesis of the ubiquitous coenzyme NAD super(+), 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 super(+) 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 super(16)HXGH super(19) active site motif in catalysis was probed by mutagenic, enzymatic and crystallographic techniques, including the characterization of an NMN super(+)/SO sub(4) super(2-) complex of mutant H19A NMNATase.