Open-to-closed transition in apo maltose-binding protein observed by paramagnetic NMR

• Published in: Nature Vol. 449; no. 7165; pp. 1078 - 1082
• Main Authors: Tang, Chun, Schwieters, Charles D, Clore, G. Marius
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 25-10-2007; Nature Publishing Group
• Subjects: Apoproteins - chemistry; Apoproteins - metabolism; Binding sites; Biological and medical sciences; Carrier Proteins - chemistry; Carrier Proteins - metabolism; Catalysis; Chemical properties; Crystal structure; Crystallography; Crystallography, X-Ray; Fundamental and applied biological sciences. Psychology; Maltose-Binding Proteins; Models, Molecular; Molecular biology; Molecular biophysics; NMR; Nuclear magnetic resonance; Nuclear Magnetic Resonance, Biomolecular - methods; Properties; Protein Binding; Protein Structure, Tertiary; Proteins; Simulation; Structure in molecular biology; Sugar; Sugars; Tridimensional structure; Trisaccharides - chemistry; Trisaccharides - metabolism; United States; Transition; Binding protein; Maltose; Nuclear magnetic resonance; Electron paramagnetic resonance; Conformation
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature06232

Large-scale domain rearrangements in proteins have long been recognized to have a critical function in ligand binding and recognition, catalysis and regulation. Crystal structures have provided a static picture of the apo (usually open) and holo usually closed) states. The general question arises as to whether the apo state exists as a single species in which the closed state is energetically inaccessible and interdomain rearrangement is induced by ligand or substrate binding, or whether the predominantly open form already coexists in rapid equilibrium with a minor closed species. The maltose-binding protein (MBP), a member of the bacterial periplasmic binding protein family, provides a model system for investigating this problem because it has been the subject of extensive studies by crystallography, NMR and other biophysical techniques. Here we show that although paramagnetic relaxation enhancement (PRE) data for the sugar-bound form are consistent with the crystal structure of holo MBP, the PRE data for the apo state are indicative of a rapidly exchanging mixture (ns to s regime) of a predominantly (∼95%) open form (represented by the apo crystal structure) and a minor (∼5%) partially closed species. Using ensemble simulated annealing refinement against the PRE data we are able to determine a 〈r-6〉 ensemble average structure of the minor apo species and show that it is distinct from the sugar-bound state.