title: Probing dimer interface stabilization within a four-helix bundle of the GrpE protein from Escherichia coli via internal deletion mutants: conversion of a dimer to monomer.
abstract: Insight into protein stability and folding remains an important area for protein research, in particular protein-protein interactions and the self-assembly of homodimers. The GrpE protein from Escherichia coli is a homodimer with a four-helix bundle at the dimer interface. Each monomer contributes a helix-loop-helix to the bundle. To probe the interface stabilization requirements, in terms of the amount of buried residues in the bundle necessary for dimer formation, internal deletion mutants (IDMs) were created that sequentially truncate each of the two helices in the helix-loop-helix region. Circular dichroism (CD) spectroscopy showed that all IDM's still contained a significant amount of α-helical secondary structure. IDM's that contained 11 or fewer of 22 residues originally present in the helices, or those that lost at least 50% of residues with less than 20% the solvent accessible surfaces (that is, hydrophobic residues) were unable to form a significant amount of dimer species as shown by chemical cross-linking. Gel filtration studies of IDM3.0 (one that retains 10 residues in each helix) show this variant to be mainly monomeric.
authors.affiliation: Department of Chemistry and the Program in Biochemistry, Knox College, 2 East South St., Galesburg, IL 61401, USA. amehl@knox.edu
authors.forename: Andrew F
authors.initials: AF
authors.lastname: Mehl
authors.forename: Nalin
authors.initials: N
authors.lastname: U G
authors.forename: Zohair
authors.initials: Z
authors.lastname: Ahmed
authors.forename: Aaron
authors.initials: A
authors.lastname: Wells
authors.forename: Tilemahos D
authors.initials: TD
authors.lastname: Spyratos
mesh_terms: D002850:Chromatography, Gel; D002942:Circular Dichroism; D017931:DNA Primers / Q000235:genetics; D019281:Dimerization; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D008958:Models, Molecular; D010957:Plasmids / Q000235:genetics; D017510:Protein Folding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017384:Sequence Deletion / Q000235:genetics
chemical_list: D017931:DNA Primers; D029968:Escherichia coli Proteins; C489400:GrpE protein, E coli; D006360:Heat-Shock Proteins