Nyström S, Wallbrandt P, Wieslander A
Department of Biochemistry, University of Umeå, Sweden.
Eur J Biochem. 1992 Feb 15;204(1):231-40. doi: 10.1111/j.1432-1033.1992.tb16629.x.
Mycoplasmas are small bacteria without a cell wall, often found as surface parasites on eukaryotic cells. Of the more than 200 membrane proteins from Acholeplasma laidlawii resolved by two-dimensional PAGE, 23 were covalently modified with acyl chains. These acyl proteins had lower pI values than average and were all labelled by different exogenously supplied radioactive fatty acids attached by O-ester bonds. The fatty acids were selectively incorporated in the order myristic acid (14:0) greater than palmitic acid (16:0) greater than stearic acid (18:0) greater than oleic acid (18:1). However, endogenously synthesised saturated fatty acids, most of which were 16:0, were preferred over the supplied ones. A fraction of the exogenous 14:0 was elongated to 16:0. Absence of saturated fatty acids increased the incorporation of 18:1. The maximum extent of modification was one acyl chain for protein T2, on the exterior surface and two acyl chains for protein D12, spanning them membrane. Exogenously supplied fatty acids were incorporated into membrane lipids in proportion to their occurrence. However, the acylated proteins always contained 8-10 times more saturated chains than did the lipids. When exogenously supplied, all A. laidlawii polar membrane lipids could donate acyl chains to the acylated proteins but the neutral fraction (fatty acids and diacylglycerol) was most efficient. An incorporation into the acylated proteins of labelled cysteine, but not glucose or glycerol, was observed. Acylated proteins with different chains interacted similarly with a Triton X-114 detergent phase, and no full-size proteins (or acylated fragments) were released from cells by proteolytic enzymes. The results indicate an anchoring with peptide segments in addition to the acyl chains. Both 14:0 and 16:0 were attached at one end of both T2 and D12, but the N-terminal methionine of T2 was not acylated. The extent of modification and preference for saturated chains in the A. laidlawii membrane acylated proteins is more similar to eukaryotic than to eubacterial proteins.
支原体是一种无细胞壁的小细菌，常作为真核细胞表面的寄生虫被发现。通过二维聚丙烯酰胺凝胶电泳解析出的来自莱氏无胆甾原体的200多种膜蛋白中，有23种被酰基链共价修饰。这些酰基化蛋白的等电点值低于平均值，并且都被通过O - 酯键连接的不同外源性供应的放射性脂肪酸标记。脂肪酸按肉豆蔻酸（14:0）>棕榈酸（16:0）>硬脂酸（18:0）>油酸（18:1）的顺序被选择性掺入。然而，内源性合成的饱和脂肪酸（其中大部分是16:0）比供应的脂肪酸更受青睐。一部分外源性的14:0被延长为16:0。饱和脂肪酸的缺失增加了18:1的掺入。修饰的最大程度是，外表面的蛋白T2有一条酰基链，跨膜的蛋白D12有两条酰基链。外源性供应的脂肪酸按其存在比例掺入膜脂中。然而，酰基化蛋白中的饱和链含量总是比脂质多8 - 10倍。当外源性供应时，所有莱氏无胆甾原体的极性膜脂都能将酰基链捐赠给酰基化蛋白，但中性部分（脂肪酸和二酰甘油）最有效。观察到标记的半胱氨酸而非葡萄糖或甘油掺入酰基化蛋白中。带有不同链的酰基化蛋白与Triton X - 114去污剂相的相互作用相似，并且没有全长蛋白（或酰基化片段）被蛋白水解酶从细胞中释放出来。结果表明除了酰基链外，还有肽段参与锚定。14:0和16:0都连接在T2和D12的一端，但T2的N端甲硫氨酸没有被酰基化。莱氏无胆甾原体膜酰基化蛋白中修饰的程度和对饱和链的偏好与真核蛋白比与真细菌蛋白更相似。
