title: A competitive low-affinity binding model for determining the mutual and specific sites of two ligands on protein.
abstract: A competitive low-affinity binding model was proposed for determining the number of mutual (overlapped) and specific binding sites of two ligands (A, B) on a protein (P). To use the model, one needs to carry out a titration experiment by adding either ligand A or B into a three-component system (A-B-P), and to monitor the spectroscopic parameter changes. Fitting the titration curve to the proposed model, one can get the mutual and specific binding sites of the two ligands on the protein. The model was examined by using human serum albumin (HSA) as a receptor and tolmetin (TOL) and salicylic acid (SAL) as ligands. Proton longitudinal relaxation rates (R1) were measured on a 500-MHz NMR spectrometer during the titration and used to derive the mutual binding sites. It was found that among the binding sites of 32+/-4 for SAL and 28+/-2 for TOL on HSA, there were 17+/-5 mutual sites for the two ligands. This result indicates that, although HSA has large binding capacities for most ligands, there are still a reasonable amount of the low-affinity binding sites that are structure selective.
authors.affiliation: State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, PR China.
authors.forename: Guoyun
authors.initials: G
authors.lastname: Bai
authors.forename: Yanfang
authors.initials: Y
authors.lastname: Cui
authors.forename: Yunhuang
authors.initials: Y
authors.lastname: Yang
authors.forename: Chaohui
authors.initials: C
authors.lastname: Ye
authors.forename: Maili
authors.initials: M
authors.lastname: Liu
mesh_terms: D000465:Algorithms; D001665:Binding Sites; D001667:Binding, Competitive / Q000187:drug effects; D006801:Humans; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D011506:Proteins / Q000737:chemistry*; D011522:Protons; D020156:Salicylic Acid / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000378:metabolism; D014046:Tolmetin / Q000378:metabolism
chemical_list: D008024:Ligands; D011506:Proteins; D011522:Protons; D012710:Serum Albumin, Bovine; D014046:Tolmetin; D020156:Salicylic Acid