Characteristics, gene expression, recombinant protein expression and enzyme activity of lipoprotein lipase in Cyprinus carpio

Lipoprotein lipase (LPL) is a key enzyme in fat hydrolysis. In order to study the gene characteristics, temporal and spatial expression distribution and enzyme activity of Cyprinus carpio LPLs (CcLPLs), the homologous genes of CcLPLs were obtained by homology searches through C. carpio genome and the sequence characteristics were analyzed. The expression analysis of CcLPLs in different tissues was carried out by qPCR. CcLPLs recombinant protein were obtained by prokaryotic expression system, and the enzyme activity of recombinant proteins was determined by p-nitrophenol method. The results are as follows. Five CcLPLs homologous genes (CcLPLA1a, CcLPLA1b, CcLPLA2a, CcLPLA2b* and CcLPLBa) were excavated from the carp genome, of which CcLPLA2b* is a pseudogene. The collinearity analysis showed that gene loss occurred during the doubling of the fish-specific genome, while the doubling of the carp-specific genome resulted in the presence of five CcLPLs in carp. By Homology analysis, CcLPLBa shared 64% indentity with CcLPLA1s and 50.8% with CcLPLA2a. qPCR showed that the expression of CcLPLs decreased by degrees in liver, heart, fat, muscle, brain, intestine and spleen. In each tissue, the expression of CcLPLA1s was significantly higher than that of CcLPLA2a, and the expression of CcLPLA2a was significantly higher than that of CcLPLBa. The expression levels of CcLPLA1s and CcLPLA2a in liver, muscle and adipose tissues under normal feeding, starvation and refeeding conditions were determined by qPCR. The results showed that the expression levels of CcLPLA1s and CcLPLA2a in liver under starvation were significantly higher than those in the normal feeding group, while the expression levels in muscle and adipose tissue were opposite to those in liver. After refeeding, the expression levels of CcLPLA1s and CcLPLA2a were restored as normal feeding group in the three tissues. Using E. coli expression system, Skp-CcLPLs and SlyD-CcLPLs recombinant proteins were obtained. The enzymatic activity of each recombinant protein was determined by the p-nitrophenol method, and the results were (24.12 ± 0.96), (22.66 ± 0.46), (21.48 ± 0.47), (21.13 ± 0.46), (18.07 ± 0.39) and (16.49 ± 0.31) U/g for SlyD-CcLPLA1a, Skp-CcLPLA1a, Skp-CcLPLBa, Skp-CcLPLA2a, SlyD-CcLPLBa and SlyD-CcLPLA2a, respectively. Regardless of Skp or SlyD tags in the recombinant proteins, the enzymatic activities of CcLPLs from high to low were CcLPLA1a, CcLPLBa and CcLPLA2a. Determination of effect of pH and NaCl concentration on enzyme activity showed the optimal reaction condition of pH was 8.0 and the NaCl concentration that exerted the maximum activity was 0.6 mol/L. In conclusion, we explored the evolutionary expression of CcLPLs homologous genes, analyzed the temporal and spatial expression of CcLPLA1s, CcLPLA2a and CcLPLBa. The effects of starvation and refeeding on the expression of CcLPLA1s and CcLPLA2a were studied, and the results revealed the lipid metabolism and response countermeasures under starvation stress, and provided a targrt for controlling the fat content in C. carpio. The prokaryotic expressions of the recombinant proteins were successfully carried out and the enzymatic activites were determined, which provided a reference for the study of fish lipoprotein lipase.