title: Template-directed protein folding into a metastable state of increased activity.
abstract: The principal objective of this work was to distinguish between kinetic and thermodynamic reaction control in protein folding. The deleterious effects of a specific mutation on spontaneous refolding competence were analyzed for this purpose. A Bowman-Birk-type proteinase inhibitor of trypsin and chymotrypsin was selected as a double-headed model protein to facilitate the detection of functional irregularities by the use of functional assays. The parent protein spontaneously folds into a single, fully active and thermodynamically stable state in a redox buffer after reduction/denaturation. By contrast, the properties of a P'1Ser-->Pro variant in the trypsin-reactive subdomain differ before and after refolding on trypsin-Sepharose. A heterogenous and thermodynamically dominant population of conformers was attained in solution. However, the enzyme-inhibitory activity of the variant was dramatically increased in the presence of trypsin-Sepharose and a stoichiometric ratio of the two subdomains was obtained as expected for a single conformation. The subsequent return for the initial mixture of conformers in solution reveals a high kinetic barrier late in the folding process. The template facilitates folding kinetically, as shown by a rate acceleration of more than four orders of magnitude. The final state was also the thermodynamically favoured one on the template, due to its increased affinity for the enzyme. The long-range effects on folding kinetics and the partial activity, and the absence of free sulfhydryl groups after refolding in solution indicate rearrangements between closely related conformers late in folding. The importance of minor structural distortions in immobilized trypsin suggests a close structural analogy between the final and the transition state of protein folding.
authors.affiliation: Institut für Physiologische Chemie und Pathobiochemie, Johannes Gutenberg Universität, Mainz, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Flecker
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D004274:DNA, Recombinant / Q000235:genetics; D014644:Genetic Variation; D007700:Kinetics; D008956:Models, Chemical; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D012996:Solutions; D013816:Thermodynamics; D014358:Trypsin Inhibitor, Bowman-Birk Soybean / Q000737:chemistry* / Q000235:genetics
chemical_list: D004274:DNA, Recombinant; D012996:Solutions; D014358:Trypsin Inhibitor, Bowman-Birk Soybean