Isothermal titration microcalorimetry reveals the cooperative and noncompetitive nature of inhibition of Sinorhizobium meliloti L5-30 dihydrodipicolinate synthase by (S)-lysine.
MosA, a dihydrodipicolinate synthase (DHDPS) from Sinorhizobium meliloti L5-30, catalyzes a class I aldolase reaction that is allosterically inhibited by (S)-lysine. The thermodynamics of (S)-lysine binding to apoenzyme, and to enzyme saturated with pyruvate or with 2-oxobutyrate, are evaluated here using isothermal titration microcalorimetry. Results unambiguously support a noncompetitive mechanism, with substrate-dependent differences in the energetics of inhibitor binding. Inhibition is strikingly cooperative: a second molecule of (S)-lysine binds 10(5) times more tightly than the first.
Phenix
Christopher P
CP
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan, Canada.
Palmer
David R J
DR
D002087:Butyrates / Q000378:metabolism; D002151:Calorimetry / Q000379:methods*; D006836:Hydro-Lyases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D008239:Lysine / Q000494:pharmacology*; D011485:Protein Binding; D019289:Pyruvic Acid / Q000378:metabolism; D016962:Sinorhizobium meliloti / Q000201:enzymology*; D013816:Thermodynamics
D002087:Butyrates; C005087:alpha-ketobutyric acid; D019289:Pyruvic Acid; D006836:Hydro-Lyases; C020040:4-hydroxy-tetrahydrodipicolinate synthase; D008239:Lysine