Spectrophotometric assay for the screening of selective enzymes towards DHA and EPA ethyl esters hydrolysis

Abstract

Polyunsaturated fatty acids (PUFAs), such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), hold notable significance due to their pharmaceutical relevance. Obtaining PUFAs from diverse sources like vegetables, fish oils, and algae poses challenges due to the mixed fatty acid (FA) composition. Therefore, focusing on particular FAs necessitates purification and resolution processes. To address this, we propose a continuous assay for screening lipases selective for ethyl EPA (E-EPA) or ethyl DHA (E-DHA). Utilizing microplate spectrophotometry, the method enables quantification of liberated fatty acids from ethyl esters (E-EPA or E-DHA). This involves assessing enzyme selectivity by measuring the release of FAs through p-nitrophenolate protonation, either separately for each substrate or in competition with a reference substrate, resorufin acetate. Ten lipases underwent screening, revealing Burkholderia cepacia lipase's (BCL) preference for ethyl DHA hydrolysis (E-EPA/E-DHA = 0.82 ± 0.07 and the lipase selectivity ratio (S) for E-EPA/E-DHA = 0.13 ± 0.04) and Candida antarctica lipase B's (CALB) high specific activity towards both E-EPA and E-DHA (531.14 ± 37.76 and 281.79 ± 2.79 U/mg, respectively) and E-EPA preference (E-EPA/E-DHA = 1.86 ± 0.15 and S E-EPA/E-DHA = 2.59±0.15). Candida rugosa recombinant isoform 4 (rCRLip4) and commercial Candida rugosa lipase (CRL) exhibited significant preference for E-EPA hydrolysis (E-EPA/E-DHA = 2.18 ±0.51 and 2.26 ±0.36, respectively; and S E-EPA/E-DHA = 7.59 ± 1.59 and 7.88 ± 2.13, respectively). Docking analyses of rCRLip4, BCL, and CALB demonstrated no statistically significant differences in activation energies or distances to the catalytic serine; however, they agreed with the experimental results. These findings suggest potential mutagenesis or directed evolution strategies for CALB to enhance E-EPA selectivity, with rCRLip4 emerging as a promising candidate for further investigation. This assay offers a valuable tool for identifying lipases with desired substrate selectivity, with broad implications for pharmaceutical and biotechnological applications.