MalE是麦芽糖/麦芽糖糊精结合蛋白(MBP),其在大多数细菌麦芽糖/麦芽糖糊精转运系统中起关键作用。先前报道的野生型MBP是包含N末端结构域（NTD）和C末端结构域（CTD）的单体，麦芽糖样分子在NTD和CTD之间被识别并被转运到细胞系统。因为MBP不进行人工二聚化,它被广泛用作蛋白质表达和纯化的标签。这里,首次报道了肠沙门氏菌的结构域交换二聚体MalE（称为SeMalE）与麦芽五糖的复合物的晶体结构，其结构与典型的单体MalE家族成员不同。在域交换二聚体中，SeMalE包含两个亚结构域:NTD和CTD。SeMalE的一个分子的NTD和CTD与伴侣分子的CTD和NTD相互作用，分别。通过NTD之间的相互作用稳定了结构域交换的二聚体构象，来自两个SeMalE分子的CTD和接头。此外,发现麦芽五糖分子位于不同SeMalE分子的NTD和CTD之间的界面处。这些结果提供了新的见解，将提高对麦芽糊精结合MalE蛋白的理解。
MalE is a maltose/maltodextrin-binding protein (MBP) that plays a critical role in most bacterial maltose/maltodextrin-transport systems. Previously reported wild-type MBPs are monomers comprising an N-terminal domain (NTD) and a C-terminal domain (CTD), and maltose-like molecules are recognized between the NTD and CTD and transported to the cell system. Because MBP does not undergo artificial dimerization, it is widely used as a tag for protein expression and purification. Here, the crystal structure of a domain-swapped dimeric MalE from Salmonella enterica (named SeMalE) in complex with maltopentaose is reported for the first time, and its structure is distinct from typical monomeric MalE family members. In the domain-swapped dimer, SeMalE comprises two subdomains: the NTD and CTD. The NTD and CTD of one molecule of SeMalE interact with the CTD and NTD of the partner molecule, respectively. The domain-swapped dimeric conformation was stabilized by interactions between the NTDs, CTDs and linkers from two SeMalE molecules. Additionally, a maltopentaose molecule was found to be located at the interface between the NTD and CTD of different SeMalE molecules. These results provide new insights that will improve the understanding of maltodextrin-binding MalE proteins.
