Yao X, Wei D, Soden C, Summers M F, Beckett D
Department of Chemistry and Biochemistry and Howard Hughes Medical Institute, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA.
Biochemistry. 1997 Dec 9;36(49):15089-100. doi: 10.1021/bi971485f.
The biotin carboxyl carrier protein (BCCP) is a subunit of acetyl-CoA carboxylase, a biotin-dependent enzyme that catalyzes the first committed step of fatty acid biosynthesis. In its functional cycle the biotin carboxyl carrier protein engages in heterologous protein-protein interactions with three distinct partners, depending on its state of posttranslational modification. Apo-BCCP interacts specifically with the biotin holoenzyme synthetase, BirA, which results in the posttranslational attachment of biotin to an essential lysine residue on BCCP. Holo-BCCP then interacts with the biotin carboxylase subunit, which leads to the addition of the carboxylate group of bicarbonate to biotin. Finally, the carboxybiotinylated form of BCCP interacts with transcarboxylase in the conversion of acetyl-CoA to malonyl-CoA. The determinants of protein-protein interaction specificity in this system are unknown. One hypothesis is that posttranslational modification of BCCP may result in conformational changes that regulate specific protein-protein interactions. To test this hypothesis, we have determined the NMR solution structure of the unbiotinylated form of an 87 residue C-terminal domain fragment of BCCP (apoBCCP87) from Escherichia coli acetyl-CoA carboxylase and compared this structure with the high-resolution structure of the biotinylated form that was recently solved by X-ray crystallographic techniques. Although the overall folding of the two proteins is highly similar, small structural differences are apparent for residues of the biotin-binding loop that may be important for mediating specific protein-protein interactions.
生物素羧基载体蛋白（BCCP）是乙酰辅酶A羧化酶的一个亚基，乙酰辅酶A羧化酶是一种生物素依赖性酶，催化脂肪酸生物合成的首个关键步骤。在其功能循环中，生物素羧基载体蛋白根据其翻译后修饰状态，与三个不同的伙伴进行异源蛋白质-蛋白质相互作用。脱辅基BCCP与生物素全酶合成酶BirA特异性相互作用，这导致生物素在翻译后附着到BCCP上一个必需的赖氨酸残基上。全酶BCCP随后与生物素羧化酶亚基相互作用，这导致将碳酸氢盐的羧基添加到生物素上。最后，BCCP的羧基生物素化形式在乙酰辅酶A转化为丙二酰辅酶A的过程中与转羧ylase相互作用。该系统中蛋白质-蛋白质相互作用特异性的决定因素尚不清楚。一种假设是，BCCP的翻译后修饰可能导致构象变化，从而调节特定的蛋白质-蛋白质相互作用。为了验证这一假设，我们确定了来自大肠杆菌乙酰辅酶A羧化酶的BCCP的87个残基C末端结构域片段的未生物素化形式（脱辅基BCCP87）的核磁共振溶液结构，并将该结构与最近通过X射线晶体学技术解析的生物素化形式的高分辨率结构进行了比较。尽管这两种蛋白质的整体折叠高度相似，但生物素结合环残基存在明显的小结构差异，这些差异可能对介导特定的蛋白质-蛋白质相互作用很重要。
