Reed K E, Cronan J E
Department of Microbiology, University of Illinois, Urbana-Champaign 61801.
J Bacteriol. 1993 Mar;175(5):1325-36. doi: 10.1128/jb.175.5.1325-1336.1993.
Two genes, lipA and lipB, involved in lipoic acid biosynthesis or metabolism were characterized by DNA sequence analysis. The translational initiation site of the lipA gene was established, and the lipB gene product was identified as a 25-kDa protein. Overproduction of LipA resulted in the formation of inclusion bodies, from which the protein was readily purified. Cells grown under strictly anaerobic conditions required the lipA and lipB gene products for the synthesis of a functional glycine cleavage system. Mutants carrying a null mutation in the lipB gene retained a partial ability to synthesize lipoic acid and produced low levels of pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase activities. The lipA gene product failed to convert protein-bound octanoic acid moieties to lipoic acid moieties in vivo; however, the growth of both lipA and lipB mutants was supported by either 6-thiooctanoic acid or 8-thiooctanoic acid in place of lipoic acid. These data suggest that LipA is required for the insertion of the first sulfur into the octanoic acid backbone. LipB functions downstream of LipA, but its role in lipoic acid metabolism remains unclear.
通过DNA序列分析对参与硫辛酸生物合成或代谢的两个基因lipA和lipB进行了表征。确定了lipA基因的翻译起始位点，并将lipB基因产物鉴定为一种25 kDa的蛋白质。LipA的过量表达导致包涵体的形成，可从中轻松纯化该蛋白质。在严格厌氧条件下生长的细胞合成功能性甘氨酸裂解系统需要lipA和lipB基因产物。在lipB基因中携带无效突变的突变体保留了部分合成硫辛酸的能力，并产生低水平的丙酮酸脱氢酶和α-酮戊二酸脱氢酶活性。lipA基因产物在体内无法将与蛋白质结合的辛酸部分转化为硫辛酸部分；然而，lipA和lipB突变体的生长都可以由6-硫辛酸或8-硫辛酸替代硫辛酸来支持。这些数据表明，将第一个硫插入辛酸主链需要LipA。LipB在LipA的下游起作用，但其在硫辛酸代谢中的作用仍不清楚。
