Nunn W D, Colburn R W, Black P N
J Biol Chem. 1986 Jan 5;261(1):167-71.
Transport of long-chain fatty acids (LCFA) across the cytoplasmic membrane of Escherichia coli requires functional fadL and fadD genes. The fadD gene codes for an acyl-CoA synthetase (fatty acid: CoA ligase (AMP forming] which has broad chain length specificity and is loosely bound to the cytoplasmic membrane. The fadL gene codes for a 43,000-dalton cytoplasmic membrane protein which, acting by an unknown mechanism, is needed specifically for LCFA transport. As a first step to define the role of the fadL gene product, studies were performed to determine if it functions as a LCFA receptor. The LCFA-binding activity was quantitated in intact cells in the absence of LCFA transport by comparing the binding of LCFA in fadD fadL and fadD fadL+ strains. These studies revealed that (i) fadD fadL+ strains bind 6-fold more LCFA than fadD fadL strains; (ii) fadD fadL strains harboring a plasmid containing the fadL gene bind 16-fold more LCFA than fadD fadL strains harboring only the plasmid vector; and (iii) the fadL-specific LCFA-binding activity is regulated by the fadR gene and catabolite repression. Studies with fadL strains harboring fadL plasmids containing in vitro constructed deletions indicate that mutations which alter the physical properties of the 43,000-dalton fadL gene product also affect fadL gene product-specific LCFA-binding activity. Overall, these studies suggest that one role of the fadL gene product in the LCFA transport process is to sequester LCFA at sites in the cell membrane for transport.
长链脂肪酸（LCFA）穿过大肠杆菌的细胞质膜需要功能性的fadL和fadD基因。fadD基因编码一种酰基辅酶A合成酶（脂肪酸：辅酶A连接酶（AMP形成）），该酶具有广泛的链长特异性，并且松散地结合在细胞质膜上。fadL基因编码一种43000道尔顿的细胞质膜蛋白，其通过未知机制发挥作用，是LCFA转运所特需的。作为确定fadL基因产物作用的第一步，进行了研究以确定它是否作为LCFA受体发挥作用。通过比较fadD fadL和fadD fadL+菌株中LCFA的结合情况，在不存在LCFA转运的完整细胞中对LCFA结合活性进行了定量。这些研究表明：（i）fadD fadL+菌株结合的LCFA比fadD fadL菌株多6倍；（ii）携带含有fadL基因的质粒的fadD fadL菌株比仅携带质粒载体的fadD fadL菌株结合的LCFA多16倍；（iii）fadL特异性的LCFA结合活性受fadR基因和分解代谢物阻遏的调节。对携带含有体外构建缺失的fadL质粒的fadL菌株的研究表明，改变43000道尔顿fadL基因产物物理性质的突变也会影响fadL基因产物特异性的LCFA结合活性。总体而言，这些研究表明fadL基因产物在LCFA转运过程中的一个作用是在细胞膜位点螯合LCFA以进行转运。
