期刊
JOURNAL OF MOLECULAR BIOLOGY
卷 389, 期 1, 页码 157-166出版社
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2009.04.008
关键词
periplasmic binding proteins; protein adaptation; ligand binding; maltose-binding protein; mal operon
资金
- Homeland Security Advanced Research Project Agency [W81XWH-05-C-0161]
- National Institutes of Health [5 DP1 OD000122-02]
- US Department of Energy
- Office of Science
- Office of Basic Energy Sciences [W-31-109-Eng-38]
Periplasmic binding proteins comprise a superfamily that is present in archaea, prokaryotes, and eukaryotes. Periplasmic binding protein ligand-binding sites have diversified to bind a wide variety of ligands. Characterization of the structural mechanisms by which functional adaptation occurs is key to understanding the evolution of this important protein superfamily. Here we present the structure and ligand-binding properties of a maltotriose-binding protein identified from the Thermus thermophilus genome sequence. We found that this receptor has a high affinity for the trisaccharide maltotriose (K-d<1 mu M) but little affinity for disaccharides that are transported by a paralogous maltose transport operon present in T. thermophilus. Comparison of this structure to other proteins that adopt the maltose-binding protein fold but bind monosaccharides, disaccharides, or trisaccharides reveals the presence of four subsites that bind individual glucose ring units. Two loops and three helical segments encode adaptations that control the presence of each subsite by steric blocking or hydrogen bonding. We provide a model in which the energetics of long-range conformational equilibria controls subsite occupancy and ligand binding. (C) 2009 Elsevier Ltd. All rights reserved.
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