title: Long-range electrostatic interactions can influence the folding, stability, and cooperativity of dihydrofolate reductase.
abstract: To test the possibility that long-range interactions might influence the folding and stability of dihydrofolate reductase, a series of single and double mutations at positions 28 and 139 were constructed and their urea-induced unfolding reactions studied by absorbance and circular dichroism spectroscopy. The alpha carbons of the two side chains are separated by 15 A in the native conformation. The replacement of Leu 28 by Arg and of Glu 139 by Gln resulted in additive effects on both kinetic and equilibrium properties of the reversible unfolding transition; no evidence for interaction was obtained. In contrast, the Arg 28/Lys 139 double replacement changed the equilibrium folding model from two state to multistate and showed evidence for interaction in one of the two kinetic phases detected in both unfolding and refolding reactions. The results can be explained in terms of a long-range, repulsive electrostatic interaction between the cationic side chains at these two positions.
authors.affiliation: Department of Chemistry, Pennsylvania State University, University Park 16802.
authors.forename: K M
authors.initials: KM
authors.lastname: Perry
authors.forename: J J
authors.initials: JJ
authors.lastname: Onuffer
authors.forename: M S
authors.initials: MS
authors.lastname: Gittelman
authors.forename: L
authors.initials: L
authors.lastname: Barmat
authors.forename: C R
authors.initials: CR
authors.lastname: Matthews
mesh_terms: D000596:Amino Acids / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D009154:Mutation; D011487:Protein Conformation; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D013762:Tetrahydrofolate Dehydrogenase