Serum opacity factor unmasks human plasma high-density lipoprotein instability via selective delipidation and apolipoprotein A-I desorption

Baiba K. Gillard, Harry Courtney, John B. Massey, Henry J. Pownall

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

Human plasma high-density lipoproteins (HDL) are important vehicles in reverse cholesterol transport, the cardioprotective mechanism by which peripheral tissue-cholesterol is transported to the liver for disposal. HDL is the target of serum opacity factor (SOF), a substance produced by Streptococcus pyogenes that turns mammalian serum cloudy. Using a recombinant (r) SOF, we studied opacification and its mechanism. rSOF catalyzes the partial disproportionation of HDL into a cholesteryl ester-rich microemulsion (CERM) and a new HDL-like particle, neo HDL, with the concomitant release of lipid-free (LF)-apo A-I. Opacification is unique; rSOF transfers apo E and nearly all neutral lipids of ∼100,-000 HDL particles into a single large CERM whose size increases with HDL-CE content (r ∼100-250 nm) leaving a neo HDL that is enriched in PL (41%) and protein (48%), especially apo A-II. rSOF is potent; within 30 min at 37°C, 10 nM rSOF opacifies 4 μM HDL. At respective low and high physiological HDL concentrations, LF-apo A-I is monomeric and tetrameric. CERM formation and apo A-I release have similar kinetics suggesting parallel or rapid sequential steps. According to the reaction products and kinetics, rSOF is a heterodivalent fusogenic protein that uses a docking site to displace apo A-I and bind to exposed CE surfaces on HDL; the resulting rSOF-HDL complex recruits additional HDL with its binding-delipidation site and through multiple fusion steps forms a CERM. rSOF may be a clinically useful and novel modality for improving reverse cholesterol transport. With apo E and a high CE content, CERM could transfer large amounts of cholesterol to the liver for disposal via the LDL receptor; neo HDL is likely a better acceptor of cellular cholesterol than HDL; LF-apo A-I could enhance efflux via the ATP-binding casette transporter ABCA1.

Original languageEnglish (US)
Pages (from-to)12968-12978
Number of pages11
JournalBiochemistry
Volume46
Issue number45
DOIs
StatePublished - Nov 13 2007

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Plasma (human)
Apolipoprotein A-I
HDL Lipoproteins
Desorption
Cholesterol Esters
Microemulsions
Cholesterol
Lipids
Apolipoproteins E
opacity factor
Liver
Apolipoprotein A-II
LDL Receptors
Streptococcus pyogenes
Reaction products
Reaction kinetics

All Science Journal Classification (ASJC) codes

  • Biochemistry

Cite this

Serum opacity factor unmasks human plasma high-density lipoprotein instability via selective delipidation and apolipoprotein A-I desorption. / Gillard, Baiba K.; Courtney, Harry; Massey, John B.; Pownall, Henry J.

In: Biochemistry, Vol. 46, No. 45, 13.11.2007, p. 12968-12978.

Research output: Contribution to journalArticle

Gillard, Baiba K. ; Courtney, Harry ; Massey, John B. ; Pownall, Henry J. / Serum opacity factor unmasks human plasma high-density lipoprotein instability via selective delipidation and apolipoprotein A-I desorption. In: Biochemistry. 2007 ; Vol. 46, No. 45. pp. 12968-12978.
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abstract = "Human plasma high-density lipoproteins (HDL) are important vehicles in reverse cholesterol transport, the cardioprotective mechanism by which peripheral tissue-cholesterol is transported to the liver for disposal. HDL is the target of serum opacity factor (SOF), a substance produced by Streptococcus pyogenes that turns mammalian serum cloudy. Using a recombinant (r) SOF, we studied opacification and its mechanism. rSOF catalyzes the partial disproportionation of HDL into a cholesteryl ester-rich microemulsion (CERM) and a new HDL-like particle, neo HDL, with the concomitant release of lipid-free (LF)-apo A-I. Opacification is unique; rSOF transfers apo E and nearly all neutral lipids of ∼100,-000 HDL particles into a single large CERM whose size increases with HDL-CE content (r ∼100-250 nm) leaving a neo HDL that is enriched in PL (41{\%}) and protein (48{\%}), especially apo A-II. rSOF is potent; within 30 min at 37°C, 10 nM rSOF opacifies 4 μM HDL. At respective low and high physiological HDL concentrations, LF-apo A-I is monomeric and tetrameric. CERM formation and apo A-I release have similar kinetics suggesting parallel or rapid sequential steps. According to the reaction products and kinetics, rSOF is a heterodivalent fusogenic protein that uses a docking site to displace apo A-I and bind to exposed CE surfaces on HDL; the resulting rSOF-HDL complex recruits additional HDL with its binding-delipidation site and through multiple fusion steps forms a CERM. rSOF may be a clinically useful and novel modality for improving reverse cholesterol transport. With apo E and a high CE content, CERM could transfer large amounts of cholesterol to the liver for disposal via the LDL receptor; neo HDL is likely a better acceptor of cellular cholesterol than HDL; LF-apo A-I could enhance efflux via the ATP-binding casette transporter ABCA1.",
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