The author responds:

Graca, Roberta; Barger, Anne M.; Hoffmann, Walter; Messick, Joanne B.; McCullough, Sheila M.

doi:10.1111/j.1939-165x.2005.tb00036.x

Cited by 4 publications

(1 citation statement)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Although heparin was observed to protect LPL from ANGPTL3 at relatively low concentrations, possibly via competitive binding, it was not able to deter the inactivating effects of ANGPTL4. Our conclusions are based on data derived from the fluorescent substrate DGGR, which, despite being an artificial substrate, makes it possible to carry out detailed real-time kinetic analysis, as done previously (32,38). Future efforts to develop a sensitive kinetic assay with native triglyceride molecules will likely strengthen the mechanistic understanding of these proteins.…”

Section: Discussionmentioning

confidence: 99%

The Angiopoietin-like Proteins ANGPTL3 and ANGPTL4 Inhibit Lipoprotein Lipase Activity through Distinct Mechanisms

Shan

Liu

et al. 2009

Journal of Biological Chemistry

127

112

View full text Add to dashboard Cite

Two members of the angiopoietin-like family of proteins, ANGPTL3 and ANGPTL4, have been shown to play important roles in modulating lipoprotein metabolism in the body. Both proteins were found to suppress lipoprotein lipase (LPL) activity in vitro as well as in vivo. However, their mechanisms of inhibition remained poorly understood. Using enzyme kinetic analysis with purified recombinant proteins, we have found key mechanistic differences between ANGPTL3 and ANGPTL4. ANGPTL3 reduced LPL catalytic activity but did not significantly alter its self-inactivation rate. In contrast, ANGPTL4 suppressed LPL by accelerating the irreversible inactivation of LPL. Furthermore, heparin was able to overcome the inhibitory effect of ANGPTL3 on LPL but not that of ANGPTL4. Site-directed mutagenesis demonstrated the critical function of Glu 40 in ANGPTL4. In contrast, when cysteine residues involved in disulfide bond formation were mutated to serines, ANGPTL4 retained its activity. Taken together, our data provide a more detailed view of the structure and mechanisms of these proteins. The finding that ANGPTL3 and ANGPTL4 inhibit LPL activity through distinct mechanisms indicates that the two proteins play unique roles in modulation of lipid metabolism in vivo. Lipoprotein lipase (LPL)2 is an essential enzyme that catalyzes the hydrolysis of triglycerides to generate free fatty acids and monoacylglycerol (for review, see Refs. 1 and 2). It is synthesized and secreted by adipocytes, macrophages, and muscle cells and then bound to the vascular endothelium by heparin sulfate proteoglycans and GPIHBP1 (glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1), a recently discovered protein (3, 4). LPL anchored as such releases free fatty acids and monoacylglycerol from triglycerides carried by chylomicron and very low density lipoprotein particles (5-9) and thus plays a major role in lipid metabolism. LPL-deficient subjects have severe hypertriglyceridemia and increased risk of arteriosclerosis (10). In contrast, subjects with slightly increased LPL activity were found to have lower triglyceride levels and decreased risk of cardiovascular diseases (11).It is well known that LPL is rapidly inactivated in vivo, but the underlying mechanism is unknown (12, 13). Recently, two secreted proteins were found to inhibit LPL activity both in vitro and in vivo. These two proteins, known as ANGPTL3 and ANGPTL4, are members of the angiopoietin-like protein family (14 -17). They share 31% overall sequence homology, with an N-terminal domain containing a coiled-coil region and a C-terminal fibrinogen-like domain that is cleaved off in vivo (16,18). Both proteins are found to inhibit LPL activity in vitro (16,18). Overexpression of ANGPTL3 and ANGTPL4 in mice led to extremely high blood levels of triglycerides and cholesterol (15, 19 -21). Knock-out of either gene in mice results in much lower blood levels of these lipids (14,(17)(18)(19)(22)(23)(24). Furthermore, post-heparin plasma LPL activity is significantly elevated in...

show abstract

Section: Discussionmentioning

confidence: 99%