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This study aimed to obtain a functional lipase (LipRM) from Ralstonia pickettii BK6 through a co-expression involving its foldase. The ORF of the LipRM was 999 bp while the gene encoding of lipase-specific foldase (LifRM) was 1,030 bp. LipRM and LifRM genes were cloned into a plasmid and were successfully co-expressed in Escherichia coli strains to produce functional LipRM. Enzyme activity from partially purified enzymes showed quite surprising results, LipRM activity in E. coli BL21 (DE3) was 25.84 U/ml, while the other strains (DH5α, HB101, S17-1λpir) were 628.98 U/ml, 761 U/ml, and 1206.46 U/ml, respectively. The highest relative activity of LipRM was found at 50-55°C and pH 7-8 with pNP-laurate (C12) as the preferred substrate specificity. LipRM activity was enhanced sharply in the presence of 30% organic solvents (methanol and ethanol) but decreased by more than 50% in the presence of detergents. This study was the first to report heterologous expression of Ralstonia pickettii lipase employing its native foldase resulting in functional lipase from subfamily I.2.

ABSTRACT Random mutagenesis technique is a powerful technique capable of producing enzymes with desired biocatalytic activity. This study aims to obtain a mutant lipase with improved hydrolytic activity on palm oil substrate using random mutagenesis technique. Random mutagenesis by error-prone PCR was used to generate mutant lipases. A total of 1101 mutants were obtained, out of which two mutants, Lip M14.25, and Lip M14.57, showed an increased relative hydrolytic activity. Lip M14.25 and Lip M14.57 demonstrated a 14% and 16% increased activity respectively. A comparison of the mutants' hydrolytic activities using p-nitrophenyl esters showed a significantly high preference for p-nitrophenyl palmitate. Furthermore, the mutant,  Lip M14.25 showed its highest activity at pH 5, and Lip M14.57 exhibited a 10 oC decrease in optimum temperature. The two mutants' protein modelling showed the substitution of N44S/S202N on M14.25 and F154L/S265C on M14.57 lipase, which caused changes in conformation and active site residue distance of the lipase. The study found two mutants of lipase, M14.25 and M14.57, which showed improved hydrolytic activity on palm oil substrate.