A new crystal form of human tear lipocalin reveals high flexibility in the loop region and induced fit in the ligand cavity
A new crystal form of human tear lipocalin reveals high flexibility in the loop region and induced fit in the ligand cavity
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DOI：
10.1107/s0907444909031011
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发表时间：
2009-10-01
影响因子：
2.2
通讯作者：
Skerra, Arne
中科院分区：
文献类型：
--
作者：
Breustedt, Daniel A.;Chatwell, Lorenz;Skerra, Arne
与人工配体1，4-丁二醇结合的泪液脂质运载蛋白（TLC）已在空间群P2（1）中结晶，在不对称单元中具有四个蛋白质分子，并且其X射线结构已在2.6埃分辨率下解出。TLC是脂质运载蛋白家族的成员，其结合具有不同化学结构的配体，例如脂肪酸、磷脂和胆固醇以及微生物铁载体和抗生素利福平。对空间群为C2的载脂蛋白薄层色谱的X射线结构分析表明，在空腔的入口处有一个较大的分叉配体口袋和一个部分无序的环区。对P2（1）晶型的分析发现了以下主要构象变化：（i）β链B、C和D;（ii）β桶开口端的环1、2和4;以及（iii）通过二硫桥连接至β桶的延伸C末端片段。结构的比较表明高的构象可塑性的环区域以及更深的部分的配体口袋，从而允许适应配体的大小和形状有很大的不同。这说明了在配体识别中混杂的机制，其也可能与脂质运载蛋白家族的一些其他生理学上重要的成员相关。
Tear lipocalin (TLC) with the bound artificial ligand 1,4-butanediol has been crystallized in space group P2(1) with four protein molecules in the asymmetric unit and its X-ray structure has been solved at 2.6 angstrom resolution. TLC is a member of the lipocalin family that binds ligands with diverse chemical structures, such as fatty acids, phospholipids and cholesterol as well as microbial siderophores and the antibiotic rifampin. Previous X-ray structural analysis of apo TLC crystallized in space group C2 revealed a rather large bifurcated ligand pocket and a partially disordered loop region at the entrace to the cavity. Analysis of the P2(1) crystal form uncovered major conformational changes (i) in beta-strands B, C and D, (ii) in loops 1, 2 and 4 at the open end of the beta-barrel and (iii) in the extended C-terminal segment, which is attached to the beta-barrel via a disulfide bridge. The structural comparison indicates high conformational plasticity of the loop region as well as of deeper parts of the ligand pocket, thus allowing adaptation to ligands that differ vastly in size and shape. This illustrates a mechanism for promiscuity in ligand recognition which may also be relevant for some other physiologically important members of the lipocalin protein family.