Ligand-free open-closed transitions of periplasmic binding proteins: the case of glutamine-binding protein.
Ligand-free open-closed transitions of periplasmic binding proteins: the case of glutamine-binding protein.
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DOI：
10.1021/bi902045p
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发表时间：
2010-03-09
期刊：
影响因子：
2.9
通讯作者：
Tjandra, Nico
中科院分区：
文献类型：
--
作者：
Bermejo, Guillermo A.;Strub, Marie-Paule;Ho, Chien;Tjandra, Nico
进行大规模结构域重排的能力对于周质结合蛋白（PBP）的底物结合功能是必不可少的，其对于革兰氏阴性菌中的营养摄取是不可缺少的。晶体结构表明PBPs通常采用“开放”无配体构型或“封闭”配体构型。然而，目前尚不清楚，作为一项一般规则，PBPs保持开放，直到配体诱导的域间关闭，或与少数人口unliganded，封闭的物种处于平衡。后者的证据最近已报道麦芽糖结合蛋白（MBP）在水溶液中通过顺磁弛豫增强（PRE），一种技术，能够探测低人口区域的构象空间。在这里，我们使用PRE来研究另一种PBP：谷氨酰胺结合蛋白（GlnBP）的无配体开闭转换。通过结合结构域的知识，分子间和浓度依赖性PRE实验，发现一组表面残基参与分子间的相互作用。除了这些残基，在两个位点（一次一个）顺磁性标记的无配体GlnBP的PRE数据可以通过无配体的开放晶体结构适当地解释，因为它既产生了良好的PRE拟合，又没有受到基于PRE的细化的显著影响。因此，与MBP相反，我们的数据并没有特别表明一个较小的封闭构象共存。几种可能性进行了探索，以解释所观察到的差异，在这种密切的结构相关的系统，其中，一个特别有趣的一个来自密切检查的域间的“铰链”区域的各种PBPs：强氢键相互作用阻碍大规模的域间动力学。
The ability to undergo large-scale domain rearrangements is essential for the substrate binding function of periplasmic binding proteins (PBPs), which are indispensable for nutrient uptake in Gram-negative bacteria. Crystal structures indicate that PBPs typically adopt either an “open” unliganded configuration or a “closed” liganded one. However, it is not clear whether, as a general rule, PBPs remain open until ligand-induced interdomain closure, or are in equilibrium with a minor population of unliganded, closed species. Evidence for the latter has been recently reported on maltose-binding protein (MBP) in aqueous solution via paramagnetic relaxation enhancement (PRE), a technique able to probe lowly populated regions of conformational space. Here, we use PRE to study the unliganded open–closed transition of another PBP: glutamine-binding protein (GlnBP). Through a combination of domain structure knowledge, and intermolecular and concentration dependence PRE experiments, a set of surface residues was found involved in intermolecular interactions. Barring such residues, PRE data on ligand-free GlnBP, paramagnetically labeled at two sites (one at a time), could be appropriately explained by the unliganded, open crystal structure in that it both yielded a good PRE fit and was not significantly affected by PRE-based refinement. Thus, contrary to MBP, our data did not particularly suggest the coexistence of a minor closed conformer. Several possibilities were explored to explain the observed differences in such closely structurally related systems, among them, a particularly interesting one arises from close inspection of the interdomain “hinge” region of various PBPs: strong hydrogen bond interactions discourage large-scale interdomain dynamics.
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