Getting the adrenaline going: crystal structure of the adrenaline-synthesizing enzyme PNMT.
BACKGROUND
Adrenaline is localized to specific regions of the central nervous system (CNS), but its role therein is unclear because of a lack of suitable pharmacologic agents. Ideally, a chemical is required that crosses the blood-brain barrier, potently inhibits the adrenaline-synthesizing enzyme PNMT, and does not affect other catecholamine processes. Currently available PNMT inhibitors do not meet these criteria. We aim to produce potent, selective, and CNS-active PNMT inhibitors by structure-based design methods. The first step is the structure determination of PNMT.


RESULTS
We have solved the crystal structure of human PNMT complexed with a cofactor product and a submicromolar inhibitor at a resolution of 2.4 A. The structure reveals a highly decorated methyltransferase fold, with an active site protected from solvent by an extensive cover formed from several discrete structural motifs. The structure of PNMT shows that the inhibitor interacts with the enzyme in a different mode from the (modeled) substrate noradrenaline. Specifically, the position and orientation of the amines is not equivalent.


CONCLUSIONS
An unexpected finding is that the structure of PNMT provides independent evidence of both backward evolution and fold recruitment in the evolution of a complex enzyme from a simple fold. The proposed evolutionary pathway implies that adrenaline, the product of PNMT catalysis, is a relative newcomer in the catecholamine family. The PNMT structure reported here enables the design of potent and selective inhibitors with which to characterize the role of adrenaline in the CNS. Such chemical probes could potentially be useful as novel therapeutics.
Martin
J L
JL
Centre for Drug Design and Development and Special Research Centre for Functional and Applied Genomics, Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD 4072, Australia. j.martin@imb.uq.edu.au
Begun
J
J
McLeish
M J
MJ
Caine
J M
JM
Grunewald
G L
GL
D001665:Binding Sites; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology; D004837:Epinephrine / Q000096:biosynthesis*; D019143:Evolution, Molecular; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D010625:Phenylethanolamine N-Methyltransferase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012435:S-Adenosylhomocysteine / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D013379:Substrate Specificity
D004791:Enzyme Inhibitors; D008024:Ligands; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D010625:Phenylethanolamine N-Methyltransferase; D004837:Epinephrine