Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands.
Structure. 2013 Oct 8;21(10):1879-88. doi: 10.1016/j.str.2013.07.020. Epub 2013 Aug 29.
The ATP-binding cassette (ABC) transporter GlnPQ is an essential uptake system for amino acids in gram-positive pathogens and related nonpathogenic bacteria. The transporter has tandem substrate-binding domains (SBDs) fused to each transmembrane domain, giving rise to four SBDs per functional transporter complex. We have determined the crystal structures and ligand-binding properties of the SBDs of GlnPQ from Enterococcus faecalis, Streptococcus pneumoniae, and Lactococcus lactis. The tandem SBDs differ in substrate specificity and affinity, allowing cells to efficiently accumulate different amino acids via a single ABC transporter. The combined structural, functional, and thermodynamic analysis revealed the roles of individual residues in determining the substrate affinity. We succeeded in converting a low-affinity SBD into a high-affinity receptor and vice versa. Our data indicate that a small number of residues that reside in the binding pocket constitute the major affinity determinants of the SBDs.
ATP 结合盒（ABC）转运蛋白 GlnPQ 是革兰氏阳性病原体和相关非致病性细菌中氨基酸的必需摄取系统。该转运蛋白的每个跨膜域都融合了一对底物结合域（SBD），每个功能转运复合物共有四个 SBD。我们已经确定了来自粪肠球菌、肺炎链球菌和乳球菌的 GlnPQ 的 SBD 的晶体结构和配体结合特性。串联 SBD 在底物特异性和亲和力上存在差异，使细胞能够通过单个 ABC 转运蛋白有效地积累不同的氨基酸。综合结构、功能和热力学分析揭示了单个残基在确定底物亲和力方面的作用。我们成功地将低亲和力 SBD 转化为高亲和力受体，反之亦然。我们的数据表明，少数位于结合口袋中的残基构成了 SBD 的主要亲和力决定因素。
