Vertebrate endothelial lipase: comparative studies of an ancient gene and protein in vertebrate evolution

Abstract

Summary Endothelial lipase (LIPG; E.C.3.1.1.3) is one of three members of the triglyceride lipase family that contributes to lipoprotein degradation within the circulation system and plays a major role in HDL metabolism in the body. In this study, in silico methods were used to predict the amino acid sequences, secondary and tertiary structures, and gene locations for LIPG genes and encoded proteins using data from several vertebrate genome projects. LIPG is located on human chromosome 18 and is distinct from 15 other human lipase genes examined. Vertebrate LIPG genes usually contained 10 coding exons located on the positive strand for most primates, as well as for horse, bovine, opossum, platypus and frog genomes. The rat LIPG gene however contained only 9 coding exons apparently due to the presence of a ‘stop’ codon’ within exon 9. Vertebrate LIPG protein subunits shared 58–97% sequence identity as compared with 38–45% sequence identities with human LIPC (hepatic lipase) and LIPL (lipoprotein lipase). Four previously reported human LIPG N-glycosylation sites were predominantly conserved among the 10 potential N-glycosylation sites observed for the vertebrate LIPG sequences examined. Sequence alignments and identities for key LIPG amino acid residues were observed as well as conservation of predicted secondary and tertiary structures with those previously reported for horse pancreatic lipase (LIPP) (Bourne et al., 1994). Several potential sites for regulating LIPG gene expression were observed including CpG islands near the 5′-untranslated regions of the human, mouse and rat LIPG genes; a predicted microRNA binding site near the 3′-untranslated region and several transcription factor binding sites within the human LIPG gene. Phylogenetic analyses examined the relationships and potential evolutionary origins of the vertebrate LIPG gene subfamily with other neutral triglyceride lipase gene families [LIPC and LIPL], other neutral lipase gene families [LIPP, LIPR1, LIPR2, LIPR3, LIPI, LIPH and LIPS], and the extended family of mammalian acid lipases (LIPA, LIPF, LIPJ, LIPK, LIPM, LIPN and LIPO). It is apparent that the triglyceride lipase ancestral gene for the vertebrate LIPG gene predated the appearance of fish during vertebrate evolution > 500 million years ago.

Bioinformatics and Evolution of Vertebrate Pancreatic Lipase and Related Proteins and Genes

“…In addition, the phylogram suggested a sequence of gene duplication events for an ancestral PTLlike gene during vertebrate evolution (see Figure 7): (1) an ancestral PTL gene duplication generating the PTL/PLR1 and PLR2 precursor genes; (2) duplication of the vertebrate PTL/PLR1 precursor gene to form the PTL and PLR1 genes; and (3) duplication of the PLR2 gene prior to primate evolution to form the PLR2 and PLR3 genes, currently observed in primate genomes. It is also apparent that vertebrate neutral lipase genes (HL; EL; and LPL) have been generated during vertebrate evolution from a distinct ancestral gene, which is consistent with previous studies on the enzymes and genes [33][34][35][36][37].…”

“…The bioinformatic methodologies used in this investigation of pancreatic lipase-like genes and proteins may be also readily applied to other pancreatic proteins as well as other gene families encoding enzymes and proteins, including neutral lipases [35][36][37], acid lipases [66], carboxylesterases [67], enolases [68] and other gene families [69][70][71].…”

“…Evolutionary studies of vertebrate PTL-like genes and proteins have been largely restricted to structural and genomic comparisons with other members of the neutral lipase gene superfamily, including lipoprotein lipases (LPL), hepatic lipases (HL), endothelial lipases (EL) and phospholipases A1 [5,10,[33][34][35][36][37]. This paper reports predicted gene structures and amino acid sequences for several vertebrate pancreatic lipase (PTL) and related protein (PLR1, PLR2 and PLR3) genes and enzymes not previously reported.…”

Vertebrate hepatic lipase genes and proteins: a review supported by bioinformatic studies

“…BLAT analyses were also undertaken for human LPL (encoding lipoprotein lipase) 9 and LIPG (encoding endothelial lipase) 6–8 (see Table 1). Structures for human, mouse, and rat isoforms (splicing variants) were obtained using the AceView website to examine predicted gene and protein structures 42 (http://www.ncbi.nlm.nih.gov/IEB/Research/Acembly/index.html?human).…”

“…1–3 HL also regulates the metabolism of low-density lipoprotein, intermediate-density lipoprotein, and high-density lipoprotein particles and is capable of catalyzing the hydrolysis of phospholipids, triglycerides, and acyl-CoA thioesters. 4,5 Endothelial lipase (EL; gene LIPG ; E.C.3.1.1.3) is a related family member that plays a major role in high-density lipoprotein cholesterol metabolism in the body, catalyzing phospholipase and triglyceride lipase activities 6–8 and lipoprotein lipase (LPL; gene LPL ; E.C.3.1.1.34) functions in the hydrolysis of triglycerides of circulating chylomicrons and very low-density lipoproteins. 9–11 These enzymes share sequence similarities (38%–44% identities) and are usually referred to as the vascular lipase gene family 7,12,13 because of their contributions to plasma lipoprotein, cholesterol, and triglyceride phenotypes and to the development of coronary heart diseases in human and animal populations.…”