Mutations that affect coenzyme binding and dimer formation of fungal 17β-hydroxysteroid dehydrogenase

Abstract

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A c c e p t e d M a n u s c r i p t 2 Keywords: 17β-hydroxysteroid dehydrogenase, site-directed mutagenesis, coenzyme binding, dimerization Abstract:The 17β-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus (17β-HSDcl) is an NADPH-dependent member of the short-chain dehydrogenase/reductase superfamily, and it functions as a dimer that is composed of two identical subunits. By constructing the appropriate mutants, we have examined the M204 residue that is situated in the coenzyme binding pocket, for its role in the binding of the coenzyme NADP(H). We have also studied the importance of hydrophobic interactions through F124, F132, F133 and F177 for 17β-HSDcl dimer formation. The M204G substitution decreased the catalytic efficiency of 17β-HSDcl, suggesting that M204 sterically coerces the nicotinamide moiety of the coenzyme into the appropriate position for further hydride transfer. Phenylalanine substitutions introduced at the dimer interface produced inactive aggregates and oligomers with high molecular masses, suggesting that these hydrophobic interactions have important roles in the formation of the active dimer.

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“…As the genes encoding 17β‐HSD enzymes from mycobacterial species have not been identified and these proteins have been only partially purified and characterized (Goren et al ., 1983; Egorova et al ., 2002a, 2005), we initially selected as enzyme candidates for metabolic engineering the well‐described 17β‐HSDs from the bacterium C. testosteroni (Schultz et al ., 1977; Lefebvre et al .,1979; Minard et al ., 1985 ; Genti‐Raimondi et al ., 1991; Yin et al ., 1991; Abalain et al ., 1993; Benach et al ., 1996, 2002; Oppermann et al ., 1997; Cabrera et al ., 2000) and the fungus C. lunatus (Plemenitas et al ., 1988; Rižner et al ., 1996, 1999, 2000, 2001a,b; Rižner and Zakelj‐Mavric, 2000; Zorko et al ., 2000; Kristan et al ., 2003, 2005, 2007a,b; Cassetta et al ., 2005; Ulrih and Lanisnik Rižner, 2006; Brunskole et al ., 2009; Svegelj et al ., 2012), because both enzymes present some relevant differences. Although they catalyse a reversible reaction and display similar reaction mechanisms, the reaction equilibrium of the fungal 17β‐HSD is shifted towards reduction, whereas the bacterial enzyme is shifted towards oxidation, as this enzyme is mainly involved into the TS catabolism in C. testosteroni (Genti‐Raimondi et al., 1990; Cabrera et al ., 2000).…”

“…To overcome the first of these factors, works to identify non‐reversible 17β‐HSDs and/or to modify the characterized enzymes by protein engineering can be explored. Several in vitro attempts have been already done to design rationally 17β‐HSD mutants from C. testosteroni and C. lunatus which present alterations in substrate specificity and/or coenzyme requirements, as well as improvements overall catalytic activity (Oppermann et al ., 1997; Kristan et al ., 2003, 2005, 2007a,b; Brunskole et al ., 2009; Svegelj et al ., 2012). To overcome the second factor, the control of bacterial metabolism by metabolic engineering and systems biology approaches would be useful.…”