Role of the carbonyl group in thioester chain length recognition by the medium chain acyl-CoA dehydrogenase.
Medium chain acyl-CoA dehydrogenase from pig kidney catalyzes the oxidation of acyl-CoA thioesters to trans-2-enoyl-CoA derivatives with an optimal chain length of about C-8. The binding energy for alkyl-SCoA thioethers shows no such optimum but increases linearly from C-2 to C-16 with a slope of about 390 cal/-CH2 group. In contrast, four types of CoA-thioester analogues (2-aza-acyl-, 3-thia-acyl-, 3-keto-acyl-, and trans-2-enoyl-) yield an incremental binding energy of about 800 cal/-CH2 group until a chain length of about C-8 is reached. The observed binding energy then decreases, or remains constant, with increasing chain length. Studies with dithiooctanoyl-CoA and 2-azadithiooctanoyl-CoA show that the C = S moiety is accommodated poorly by the medium chain dehydrogenase. A model for chain length discrimination, based on the crystal structure of the enzyme [Kim, J. J. P., Wang, M., & Paschke, R. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 7523-7527], is proposed in which hydrogen-bonding interactions between enzyme and thioester carbonyl oxygen atom are maximized at optimal chain lengths. Oversized chains decrease the frequency of effective alignment between enzyme and the C-1 to C-3 region of thioester ligands. Thus the extent of polarization of bound 4-thia-trans-2-enoyl-CoA thioesters decreases sharply with chains longer than C-12.(ABSTRACT TRUNCATED AT 250 WORDS)
Trievel
R C
RC
Department of Chemistry and Biochemistry, University of Delaware, Newark 19716, USA.
Wang
R
R
Anderson
V E
VE
Thorpe
C
C
D042964:Acyl-CoA Dehydrogenase; D044944:Acyl-CoA Dehydrogenases / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D002942:Circular Dichroism; D003065:Coenzyme A / Q000737:chemistry; D004952:Esters / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000201:enzymology; D009682:Magnetic Resonance Spectroscopy; D013056:Spectrophotometry, Ultraviolet; D013379:Substrate Specificity; D013552:Swine; D013816:Thermodynamics
D004952:Esters; D044944:Acyl-CoA Dehydrogenases; D042964:Acyl-CoA Dehydrogenase; D003065:Coenzyme A