Pugliese L, Malcovati M, Coda A, Bolognesi M
Dipartimento di Genetica e Microbiologia, Università di Pavia, Italy.
J Mol Biol. 1994 Jan 7;235(1):42-6. doi: 10.1016/s0022-2836(05)80010-5.
The three-dimensional structure of hen egg-white apo-avidin, crystallized in a tetragonal crystal form, has been refined to a crystallographic R-factor of 0.164 (for the 6390 observed reflections in the 10.0 to 2.8 A resolution range). As in the case of holo-avidin, from which starting atomic co-ordinates were derived, the functional tetramer shows 2-pseudo 22 molecular symmetry. Each promoter is organized in an eight-stranded antiparallel orthogonal beta-barrel, with extended loop regions, which define the biotin binding pocket in the protomer core. In the absence of biotin the binding site is only partly occupied by water molecules. The structure of the binding site residues, as observed in apo-avidin, is highly complementary to that of the incoming biotin molecule, accounting for prompt and specific recognition. A crystal lattice contact may play a role in stabilizing the conformation of one protein loop, part of the biotin-binding pocket.
以四方晶型结晶的鸡蛋清脱辅基抗生物素蛋白的三维结构已被精修至晶体学R因子为0.164（对于在10.0至2.8埃分辨率范围内观察到的6390个反射）。如同从中导出起始原子坐标的全抗生物素蛋白的情况一样，功能性四聚体显示出2-伪22分子对称性。每个亚基由一个八链反平行正交β-桶组成，具有延伸的环区域，这些区域在亚基核心中定义了生物素结合口袋。在没有生物素的情况下，结合位点仅部分被水分子占据。在脱辅基抗生物素蛋白中观察到的结合位点残基的结构与进入的生物素分子的结构高度互补，这解释了快速而特异性的识别。晶格接触可能在稳定一个蛋白质环（生物素结合口袋的一部分）的构象中起作用。
