Title : Glycosylation of
endothelial lipase at
asparagine-116 reduces activity and the hydrolysis of native
lipoproteins in vitro and in vivo
Abstract :
- We previously identified that four of five putative N-linked glycosylation sites of human endothelial lipase ( EL ) are utilized and suggested that the substitution of asparagine-116 ( Asn-116 ) with alanine ( Ala ) (N116A) increased the hydrolytic activity of EL
- The current study demonstrates that mutagenesis of either Asn-116 to threonine ( Thr ) or Thr-118 to Ala also disrupted the glycosylation of EL and enhanced catalytic activity toward synthetic substrates by 3-fold versus wild-type EL
- Furthermore, we assessed the hydrolysis of native lipoprotein lipids by EL-N116A
- EL-N116A exhibited a 5-fold increase in LDL hydrolysis and a 1.8-fold increase in HDL2 hydrolysis
- Consistent with these observations, adenovirus-mediated expression of EL-N116A in mice significantly reduced the levels of both LDL and HDL cholesterol beyond the reductions observed by the expression of wild-type EL alone
- Finally, we introduced Asn-116 of EL into the analogous positions within LPL and HL, resulting in N-linked glycosylation at this site
- Glycosylation at this site suppressed the LPL hydrolysis of synthetic substrates, LDL, HDL2 , and HDL3 but had little effect on HL activity
- These data suggest that N-linked glycosylation at Asn-116 reduces the ability of EL to hydrolyze lipids in LDL and HDL2