Electrostatic interactions are among the key factors determining the structure and function of proteins. Here we report experimental results that illuminate the functional importance of local dipoles to these interactions. The refined 1.7-A X-ray str ...
Electrostatic interactions are among the key factors determining the structure and function of proteins. Here we report experimental results that illuminate the functional importance of local dipoles to these interactions. The refined 1.7-A X-ray structure of the liganded form of the sulfate-binding protein, a primary sulfate active transport receptor of Salmonella typhimurium, shows that the sulfate dianion is completely buried and bound by hydrogen bonds (mostly main-chain peptide NH groups) and van der Waals forces. The sulfate is also closely linked, via one of these peptide units, to a His residue. It is also adjacent to the N-termini of three alpha-helices, of which the two shortest have their C-termini "capped" by Arg residues. Site-directed mutagenesis of the recombinant Escherichia coli sulfate receptor had no effect on sulfate-binding activity when an Asn residue was substituted for the positively charged His and the two Arg (changed singly and together) residues. These results, combined with other observations, further solidify the idea that stabilization of uncompensated charges in a protein is a highly localized process that involves a collection of local dipoles, including those of peptide units confined to the first turns of helices. The contribution of helix macrodipoles appears insignificant.
Related Citations:
Sulfate-Binding Protein Dislikes Protonated Oxyacids. A Molecular Explanation Jacobson, B.L.,Quiocho, F.A. (1988) J.Mol.Biol. 204: 783
Amino Acid Sequence of the Sulfate-Binding Protein from Salmonella Typhimurium Lt2 Isihara, H.,Hogg, R.W. (1980) J.Biol.Chem. 255: 4614
The 2 Angstroms Resolution Structure of the Sulfate-Binding Protein Involved in Active Transport in Salmonella Typhimurium Pflugrath, J.W.,Quiocho, F.A. (1988) J.Mol.Biol. 200: 163
Engineered Interdomain Disulfide in the Periplasmic Receptor for Sulfate Transport Reduces Flexibility. Site-Directed Mutagenesis and Ligand-Binding Studies Jacobson, B.L.,He, J.J.,Vermersch, P.S.,Lemon, D.D.,Quiocho, F.A. (1991) J.Biol.Chem. 266: 5220
Sulphate Sequestered in the Sulphate-Binding Protein of Salmonella Typhimurium is Bound Solely by Hydrogen Bonds Pflugrath, J.W.,Quiocho, F.A. (1985) Nature 314: 257
Organizational Affiliation:
Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas 77030.
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