Comparative Analyses of Lipoprotein Lipase, Hepatic Lipase, and Endothelial Lipase, and Their Binding Properties with Known Inhibitors
and Their Binding Properties
with Known Inhibitors. PLoS ONE 8(8): e72146. doi:10.1371/journal.pone.0072146
Comparative Analyses of Lipoprotein Lipase, Hepatic Lipase, and Endothelial Lipase, and Their Binding Properties with Known Inhibitors
Ziyun Wang 0
Shen Li 0
Lidan Sun 0
Jianglin Fan 0
Zhenming Liu 0
Paul Taylor, University of Edinburgh, United Kingdom
0 1 State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University , Beijing , P. R. China , 2 Department of Molecular Pathology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi , Yamanashi , Japan
The triglyceride lipase gene subfamily plays a central role in lipid and lipoprotein metabolism. There are three members of this subfamily: lipoprotein lipase, hepatic lipase, and endothelial lipase. Although these lipases are implicated in the pathophysiology of hyperlipidemia and atherosclerosis, their structures have not been fully solved. In the current study, we established homology models of these three lipases, and carried out analysis of their activity sites. In addition, we investigated the kinetic characteristics for the catalytic residues using a molecular dynamics simulation strategy. To elucidate the molecular interactions and determine potential key residues involved in the binding to lipase inhibitors, we analyzed the binding pockets and binding poses of known inhibitors of the three lipases. We identified the spatial consensus catalytic triad ''Ser-Asp-His'', a characteristic motif in all three lipases. Furthermore, we found that the spatial characteristics of the binding pockets of the lipase molecules play a key role in ligand recognition, binding poses, and affinities. To the best of our knowledge, this is the first report that systematically builds homology models of all the triglyceride lipase gene subfamily members. Our data provide novel insights into the molecular structures of lipases and their structure-function relationship, and thus provides groundwork for functional probe design towards lipase-based therapeutic inhibitors for the treatment of hyperlipidemia and atherosclerosis.
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Funding: This work was supported by the National Natural Science Foundation of China (Grant No. 21272017, 20802006) and National High Technology
Research and Development Program of China (Grant No. 2012AA020308). These funders had no role in study design, data collection and analysis, decision to
publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
The triglyceride lipase gene subfamily (TLGS) is comprised of
three evolutionarily related lipases: lipoprotein lipase (LPL),
hepatic lipase (HL), and endothelial lipase (EL), and plays a
central role in plasma lipoprotein metabolism and homeostasis [1].
These lipases are differentiated by their tissue-specific gene
expression, and substrate specificity. LPL is mainly expressed in
adipose and muscle tissues, while HL is specifically expressed in
the liver [2,3]. In contrast, EL is a newly identified lipase that is
synthesized by vascular endothelial cells, thyroid epithelial cells,
and hepatocytes [4]. LPL mainly hydrolyzes the triglycerides of
chylomicrons and very low-density lipoproteins, whereas EL exerts
significant phospholipase activity on high-density lipoprotein
(HDL) particles, but has less triglyceride lipase activity [2,46].
HL seems to have equal hydrolytic activity on triglycerides,
phospholipids of remnant lipoproteins, and HDL particles [7].
Furthermore, all lipases are expressed in macrophages and have
been implicated in the pathogenesis of atherosclerosis [710].
Because of their diverse range of important functions in
maintaining lipoprotein homeostasis and their involvement in
the pathophysiology of hyperlipidemia and atherosclerosis, the
TLGS members are attractive biomarkers and potential
therapeutic targets for the treatment of metabolic diseases [11]. For
example, the up-regulation of LPL activity may be beneficial in
obesity and diabetes, whereas inhibition of EL may increase
plasma HDL levels [12,13]. It is therefore essential to obtain
molecular structural information to elucidate how these lipases
exert their effects, and how they interact with their ligands.
Previous studies have revealed that these lipases share common
motifs, including a heparin-binding domain, and key active site
residues (called the a/b hydrolase fold) [14]. The active site
residues are responsible for maintaining the juxtaposition of the
conserved residues in the active site pentapeptide, and evolved
independently from the forces that constrained and molded the
analogous pentapeptide of serine proteases [15]. It is likely that
these two motifs are a result of convergent evolution [16]. Each
lipase molecule has a lid element, which blocks the enzymatic
active site, and cofactors that are required for enzymatic
activation. For example, apolipoprotei (...truncated)