title: Thermodynamic effects of replacements of Pro residues in helix interiors of maltose-binding protein.
abstract: Introduction of Pro residues into helix interiors results in protein destabilization. It is currently unclear if the converse substitution (i.e., replacement of Pro residues that naturally occur in helix interiors would be stabilizing). Maltose-binding protein is a large 370-amino acid protein that contains 21 Pro residues. Of these, three nonconserved residues (P48, P133, and P159) occur at helix interiors. Each of the residues was replaced with Ala and Ser. Stabilities were characterized by differential scanning calorimetry (DSC) as a function of pH and by isothermal urea denaturation studies as a function of temperature. The P48S and P48A mutants were found to be marginally more stable than the wild-type protein. In the pH range of 5-9, there is an average increase in T(m) values of P48A and P48S of 0.4 degrees C and 0.2 degrees C, respectively, relative to the wild-type protein. The other mutants are less stable than the wild type. Analysis of the effects of such Pro substitutions in MBP and in three other proteins studied to date suggests that substitutions are more likely to be stabilizing if the carbonyl group i-3 or i-4 to the mutation site is not hydrogen bonded in the wild-type protein.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India.
authors.forename: R S
authors.initials: RS
authors.lastname: Prajapati
authors.forename: G M
authors.initials: GM
authors.lastname: Lingaraju
authors.forename: Kiran
authors.initials: K
authors.lastname: Bacchawat
authors.forename: Avadhesha
authors.initials: A
authors.lastname: Surolia
authors.forename: Raghavan
authors.initials: R
authors.lastname: Varadarajan
mesh_terms: D019943:Amino Acid Substitution; D001665:Binding Sites / Q000235:genetics; D002151:Calorimetry / Q000379:methods; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics; D005838:Genotype; D006863:Hydrogen-Ion Concentration; D058619:Maltose-Binding Proteins; D009154:Mutation; D011392:Proline / Q000737:chemistry* / Q000235:genetics; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013696:Temperature; D013816:Thermodynamics; D014508:Urea / Q000737:chemistry
chemical_list: D002352:Carrier Proteins; D058619:Maltose-Binding Proteins; D014508:Urea; D011392:Proline