Development of thermostable lipase B from Candida antarctica (CalB) through in silico design employing B-factor and RosettaDesign

Organic synthesis reactions demand improved characteristics of enzymes than wild type such as reactivity, thermostability, enantioselectivity and so on. Especially thermostability of enzyme is highly important since reaction at higher temperature has many advantages such as elevated reaction rate and increased solubility of substrates. Due to this requirement, a rational approach was employed to develop thermostable CalB. The first step of this approach was the selection of appropriate sites showing a high ‘B-factor’ value. These sites were chosen on the basis of atomic displacement parameters obtained from X-ray data. These selected sites were then substituted with other amino acids that were determined to be more rigid than the original amino acids by computational modeling using ‘RosettaDesign’. As a result of this rational approach, several thermostable CalB mutants including R249L were produced. The residual activity of R249L CalB was two times higher than that of wild type CalB at 55 °C. Melting temperature (Tm) of R249L mutant increased to 56.8 °C compared with wild type CalB (Tm: 54.5 °C), which was determined by DSF (differential scanning fluorimetry). Additionally, packing analysis tool “Voronoia” pointed out that one cavity close to residue 249 of wild type CalB disappeared in CalB R249L, which could be the reason for the increase in thermal stability of CalB R249L mutant compared wild type CalB.