title: Solution NMR structures of IgG binding domains with artificially evolved high levels of sequence identity but different folds.
abstract: We describe here the solution NMR structures of two IgG binding domains with highly homologous sequences but different three-dimensional structures. The proteins, G311 and A219, are derived from the IgG binding domains of their wild-type counterparts, protein G and protein A, respectively. Through a series of site-directed mutations and phage display selections, the sequences of G311 and A219 were designed to converge to a point of high-level sequence identity while keeping their respective wild-type tertiary folds. Structures of both artificially evolved sequences were determined by NMR spectroscopy. The main chain fold of G311 can be superimposed on the wild-type alpha/beta protein G structure with a backbone rmsd of 1.4 A, and the A219 structure can be overlaid on the wild-type three-alpha-helix protein A fold also with a backbone rmsd of 1.4 A. The structure of G311, in particular, accommodates a large number of mutational changes without undergoing a change in the overall fold of the main chain. The structural differences are maintained despite a high level (59%) of sequence identity. These proteins serve as starting points for further experiments that will probe basic concepts of protein folding and conformational switching.
authors.affiliation: Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, 9600 Gudelsky Drive, Rockville, Maryland 20850, USA.
authors.forename: Yanan
authors.initials: Y
authors.lastname: He
authors.forename: Deok Cheon
authors.initials: DC
authors.lastname: Yeh
authors.forename: Patrick
authors.initials: P
authors.lastname: Alexander
authors.forename: Philip N
authors.initials: PN
authors.lastname: Bryan
authors.forename: John
authors.initials: J
authors.lastname: Orban
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D007074:Immunoglobulin G / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013205:Staphylococcal Protein A / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: C029152:G-substrate; D007074:Immunoglobulin G; D009419:Nerve Tissue Proteins; D013205:Staphylococcal Protein A