Enzyme-assisted suicide: molecular basis for the antifungal activity of 5-hydroxy-4-oxonorvaline by potent inhibition of homoserine dehydrogenase.
The structure of the antifungal drug 5-hydroxy-4-oxonorvaline (HON) in complex with its target homoserine dehydrogenase (HSD) has been determined by X-ray diffraction to 2.6 A resolution. HON shows potent in vitro and in vivo activity against various fungal pathogens despite its weak (2 mM) affinity for HSD in the steady state. The structure together with structure-activity relationship studies, mass spectrometry experiments, and spectroscopic data reveals that the molecular mechanism of antifungal action conferred by HON involves enzyme-dependent formation of a covalent adduct between C4 of the nicotinamide ring of NAD(+) and C5 of HON. Furthermore, novel interactions are involved in stabilizing the (HON*NAD)-adduct, which are not observed in the enzyme's ternary complex structure. These findings clarify the apparent paradox of the potent antifungal actions of HON given its weak steady-state inhibition characteristics.
Antimicrobial Research Centre and Department of Biochemistry, McMaster University, Hamilton L8N 3Z5, Canada.
Suzanne L
SL
Jacques
I Ahmad
IA
Mirza
Linda
L
Ejim
Kalinka
K
Koteva
Donald W
DW
Hughes
Kirk
K
Green
Robert
R
Kinach
John F
JF
Honek
Hoi Kiong
HK
Lai
Albert M
AM
Berghuis
Gerard D
GD
Wright
D000622:Aminolevulinic Acid / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology*; D000935:Antifungal Agents / Q000494:pharmacology*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006715:Homoserine Dehydrogenase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D009243:NAD / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship
D000935:Antifungal Agents; D004791:Enzyme Inhibitors; D009243:NAD; C058222:2-amino-5-hydroxy-4-oxopentanoic acid; D000622:Aminolevulinic Acid; D006715:Homoserine Dehydrogenase