Ali S T, Moir A J, Ashton P R, Engel P C, Guest J R
Krebs Institute, Department of Molecular Biology and Biotechnology, Sheffield, UK.
Mol Microbiol. 1990 Jun;4(6):943-50. doi: 10.1111/j.1365-2958.1990.tb00667.x.
The overexpression of a subgene encoding a hybrid lipoyl domain of the dihydrolipoamide acetyltransferase component of the pyruvate dehydrogenase complex of Escherichia coli has previously been shown to result in the formation of lipoylated and unlipoylated products. Overexpression of the same subgene in a lipoic acid biosynthesis mutant growing under lipoate-deficient conditions has now been shown to produce domains modified by octanoylation as well as unmodified domains. It was concluded from the mass of a lipoyl-binding-site peptide that the modification involves N6-octanoylation of the lysine residue (Lys244) that is normally lipoylated, and this was confirmed by the trypsin-insensitivity of the corresponding Lys244-Ala-245 bond, and the absence of modification in a mutant domain in which Lys244 is replaced by Gln. This novel protein modification raises interesting questions concerning the pathway of lipoic acid biosynthesis and the mechanism of enzyme lipoylation.
先前已表明，编码大肠杆菌丙酮酸脱氢酶复合体二氢硫辛酰胺乙酰转移酶组分的杂合硫辛酰结构域的亚基因的过表达会导致硫辛酰化和未硫辛酰化产物的形成。现在已表明，在硫辛酸生物合成突变体中，在硫辛酸缺乏条件下生长时，同一亚基因的过表达会产生经辛酰化修饰的结构域以及未修饰的结构域。根据硫辛酰结合位点肽的质量得出结论，该修饰涉及通常被硫辛酰化的赖氨酸残基（Lys244）的N6-辛酰化，相应的Lys244-Ala-245键对胰蛋白酶不敏感以及在Lys244被Gln取代的突变结构域中不存在修饰证实了这一点。这种新的蛋白质修饰引发了有关硫辛酸生物合成途径和酶硫辛酰化机制的有趣问题。
