Analogs of palmitoyl-CoA that are substrates for myristoyl-CoA:protein N-myristoyltransferase.
Saccharomyces cerevisiae myristoyl-CoA:protein N-myristoyltransferase (Nmt1p; EC 2.3.1.97) is an essential enzyme that is highly selective for myristoyl-CoA in vivo. It is unclear why myristate (C14:0), a rare cellular fatty acid, has been selected for this covalent protein modification over more abundant fatty acids such as palmitate (C16:0), nor is it obvious how the enzyme's acyl-CoA binding site is able to discriminate between these two fatty acids. Introduction of a cis double bond between C5 and C6 of palmitate [(Z)-5-hexadecenoic acid] or a triple bond between C4 and C5 or C6 and C7 (Y4- and Y6-hexadecenoic acids) yields compounds that, when converted to their CoA derivatives, approach the activity of myristoyl-CoA as Nmt1p substrates in vitro. Kinetic studies of 42 C12-C18 fatty acids containing triple bonds, para-phenylene, or a 2,5-furyl group, as well as cis and trans double bonds, suggest that the geometry of the enzyme's acyl-CoA binding site requires that the acyl chain of active substrates assume a bent conformation in the vicinity of C5. Moreover, the distance between C1 and the bend appears to be a critical determinant for optimal positioning of the acyl-CoA in this binding site so that peptide substrates can subsequently bind in the sequential ordered bi-bi reaction mechanism. Identification of active, conformationally restricted analogs of palmitate offers an opportunity to "convert" wild-type or mutant Nmts to palmitoyltransferases so that they can deliver these C16 fatty acids to critical N-myristoylproteins in vivo. nmt181p contains a Gly-451-->Asp mutation, which causes a marked reduction in the enzyme's affinity for myristoyl-CoA. Strains of S. cerevisiae containing nmt1-181 exhibit temperature-sensitive myristic acid auxotrophy: their complete growth arrest at 37 degrees C is relieved when the medium is supplemented with 500 microM C14:0 but not with C16:0. The CoA derivatives of (Z)-5-hexadecenoic and Y6-hexadecynoic acids are as active substrates for the mutant enzyme as myristoyl-CoA at 24 degrees C. However, unlike C16:0, they produce growth arrest of nmt181p-producing cells at this "permissive" temperature, suggesting that these C16 fatty acids do not allow expression of the biological functions of essential S. cerevisiae N-myristoylproteins.
Rudnick
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DA
Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, MO 63110.
Lu
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Jackson-Machelski
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Hernandez
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JC
Li
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Gokel
G W
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Gordon
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JI
D000214:Acyl Coenzyme A / Q000378:metabolism*; D000217:Acyltransferases / Q000378:metabolism*; D007700:Kinetics; D010171:Palmitoyl Coenzyme A / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D000214:Acyl Coenzyme A; D010171:Palmitoyl Coenzyme A; D000217:Acyltransferases; C050480:glycylpeptide N-tetradecanoyltransferase