In silico and experimental investigations were conducted to explore the effects of substituting hydrophobic residues, Val, Met, Leu, Ile, Trp, and Phe into Gln 114 of T1 lipase. The in silico investigations accurately predicted the enzymatic characteristics of the mutants in the experimental studies and provided rationalization for some of the experimental observations. Substitution with Leu successfully improved the conformational stability and enzymatic characteristics of T1 lipase. However, replacement of Gln114 with Trp negatively affected T1 lipase and resulted in the largest disruption of protein stability, diminished lipase activity and inferior enzymatic characteristics. These results suggested that the substitution of a larger residue in a densely packed area of the protein core can have considerable effects on the structure and function of an enzyme. This is especially true when the residue is next to the catalytic serine as demonstrated with the Phe and Trp mutation.
The bioconversion of vitamin D3 catalyzed by cytochrome P450 (CYP) requires 25-hydroxylation and subsequent 1α-hydroxylation to produce the hormonal activated 1α,25-dihydroxyvitamin D3. Vitamin D3 25-hydroxylase catalyses the first step in the vitamin D3 biosynthetic pathway, essential in the de novo activation of vitamin D3. A CYP known as CYP107CB2 has been identified as a novel vitamin D hydroxylase in Bacillus lehensis G1. In order to deepen the understanding of this bacterial origin CYP107CB2, its detailed biological functions as well as biochemical characteristics were defined. CYP107CB2 was characterized through the absorption spectral analysis and accordingly, the enzyme was assayed for vitamin D3 hydroxylation activity. CYP-ligand characterization and catalysis optimization were conducted to increase the turnover of hydroxylated products in an NADPH-regenerating system. Results revealed that the over-expressed CYP107CB2 protein was dominantly cytosolic and the purified fraction showed a protein band at approximately 62 kDa on SDS-PAGE, indicative of CYP107CB2. Spectral analysis indicated that CYP107CB2 protein was properly folded and it was in the active form to catalyze vitamin D3 reaction at C25. HPLC and MS analysis from a reconstituted enzymatic reaction confirmed the hydroxylated products were 25-hydroxyitamin D3 and 1α,25-dihydroxyvitamin D3 when the substrates vitamin D3 and 1α-hydroxyvitamin D3 were used. Biochemical characterization shows that CYP107CB2 performed hydroxylation activity at 25 °C in pH 8 and successfully increased the production of 1α,25-dihydroxyvitamin D3 up to four fold. These findings show that CYP107CB2 has a biologically relevant vitamin D3 25-hydroxylase activity and further suggest the contribution of CYP family to the metabolism of vitamin D3.