Showing papers on "Salt bridge (protein and supramolecular) published in 1988"
TL;DR: The data support the conclusion that the electron self-exchange takes place by way of the hydrophobic surface patch around His117, and that His35 is not involved in this reaction.
55 citations
TL;DR: The calculation suggests that the ion-pair contribution to the binding energy is insignificant, as the enzyme surroundings do not stabilize the salt bridge to the extent of the desolvation of the charged groups.
Abstract: The importance of the ionic interaction due to the formation of the salt bridge between the Asp-27 and the pteridine ring in Escherichia coli dihydrofolate reductase-methotrexate complex has been studied by using the free-energy perturbation method. The calculation suggests that the ion-pair contribution to the binding energy is insignificant, as the enzyme surroundings do not stabilize the salt bridge to the extent of the desolvation of the charged groups. The activation barrier for the proton exchange between the pteridine ring and the Asp-27 is calculated to be 20.1 kcal/mol (1 cal = 4.184 J) by using the coordinate-coupled perturbation method, implying that this may be a channel to the proton exchange from the pteridine ring to the solvent. The Gibbs-energy difference of binding between the Asn-27 and Ser-27 is calculated to be 3.2 kcal/mol and is mainly due to the electrostatic interactions.
54 citations
TL;DR: The changes in the band at 1562 cm-1 indicate that when the two proteins interact, three ionized carboxyl groups of Glu become involved in salt bridge formation, suggesting that infrared spectroscopy may be a rapid and quantitative method for the study of ionic interactions between proteins.
Abstract: The infrared spectrum of a solution of a protein contains bands due to both the peptide backbone and the amino acid side chains. Generally, the bands due to the peptide backbone, between 1700 and 1600 cm-1, are analyzed to determine the secondary structure of the protein; the bands due to the amino acid side chains, between 1600 and 1500 cm-1, are largely ignored. When cytochrome b5 is mixed with cytochrome c, under conditions that favor ionic complex formation, changes are seen in protein secondary structure and also in a band at 1562 cm-1. The band at 1562 cm-1 is due to the side-chain carboxyl of Glu residues, rather than those of Asp residues that show a band at 1585 cm-1, and the changes in the band at 1562 cm-1 indicate that when the two proteins interact, three ionized carboxyl groups of Glu become involved in salt bridge formation. This result is identical with that obtained by previous theoretical studies and suggests that infrared spectroscopy may be a rapid and quantitative method for the study of ionic interactions between proteins.
28 citations
13 citations