Construction of a Thermally Stable Cholesterol Oxidase Mutant by Site-Directed Mutagenesis

• Published in: Biotechnology (Faisalābād, Pakistan) Pakistan), 2008-12, Vol.7 (4), p.826-829
• Main Authors: Ghasemian, A., T. Yazdi, M., Sepehrizad, Z.
• Format: Article
• Language: English
• Subjects: Rhodococcus
• ISSN: 1682-296X
• DOI: 10.3923/biotech.2008.826.829

Site-directed mutagenesis was used for improvement of thermal stability of cholesterol oxidase from Rhodococcus sp. PTCC 1633. Cholesterol oxidase catalyzes the oxidation of cholesterol to cholest-5-en-3-one and its subsequent isomerization into cholest-4-en-3-one. This enzyme is industrially important and is commonly used for the enzymatic transformation of cholesterol. It is also useful for the clinical determination of total or free serum cholesterol by coupling with a related enzyme for the assessment of arteriosclerosis and other lipid disorders. Substitution in glutamine145 was created by means of site-directed mutagenesis using SOE-PCR (Splicing by Overlap Extension-Polymerase Chain Reaction). The presence of directed mutations and adventitious base changes were verified by DNA sequencing. The properties of mutant enzyme were similar to those of the wild type but the thermal stability of enzyme was obviously increased. Also, the range of pH for activity of mutant enzyme differed from that of the wild-type cholesterol oxidase. Substitution of the glutamine (Q) 145 by glutamic acid (E) could create not only a hydrogen bond between glutamic acid (E) 145 and aspartic acid (D) 134, but also a salt bridge between glutamic acid (E) 145 and arginine (R) 147 and subsequently improve the thermal activity of cholesterol oxidase.