Conformational stability of 17β-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus

Abstract

The functional activities of proteins are closely related to their molecular structure and understanding their structure-function relationships remains one of the intriguing problems of molecular biology. We investigated structural changes in 17β-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus (17β-HSDcl) induced by pH, temperature, salt, urea, guanidine hydrochloride, and coenzyme NADPH binding. At 25°C and within the relatively narrow pH range of 7.0-9.0, 17β-HSDcl exists in its native conformation as a dimer. This native conformation is thermally stable up to 40°C in this pH range. At 25°C and pH 2.0 in the presence of 150-300 mm NaCl, 17β-HSDcl forms soluble aggregates enriched in α-helical and β-sheet structures. At higher temperatures and NaCl concentrations, these soluble aggregates start to precipitate. The denaturants urea and guanidine hydrochloride unfold 17β-HSDcl at concentrations of 1.2 and 0.4 m, respectively. Binding of the coenzyme NADPH to 17β-HSDcl causes local structural changes that do not significantly affect the thermal stability of this protein. © 2006 The Authors.