Tyrosine 192 in apolipoprotein A-I is the major site of nitration and chlorination by myeloperoxidase, but only chlorination markedly impairs ABCA1-dependent cholesterol transport.

Abstract

High density lipoprotein (HDL) isolated from human atherosclerotic lesions and the blood of patients with established coronary artery disease contains elevated levels of 3-nitrotyrosine and 3-chlorotyrosine. Myeloperoxidase (MPO) is the only known source of 3-chlorotyrosine in humans, indicating that MPO oxidizes HDL in vivo. In the current studies, we used tandem mass spectrometry to identify the major sites of tyrosine oxidation when lipid-free apolipoprotein A-I (apoA-I), the major protein of HDL, was exposed to MPO or peroxynitrite (ONOO(-)). Tyrosine 192 was the predominant site of both nitration and chlorination by MPO and was also the major site of nitration by ONOO(-). Electron paramagnetic spin resonance studies of spin-labeled apoA-I revealed that residue 192 was located in an unusually hydrophilic environment. Moreover, the environment of residue 192 became much more hydrophobic when apoA-I was incorporated into discoidal HDL, and Tyr(192) of HDL-associated apoA-I was a poor substrate for nitration by both myeloperoxidase and ONOO(-), suggesting that solvent accessibility accounted in part for the reactivity of Tyr(192). The ability of lipid-free apoA-I to facilitate ATP-binding cassette transporter A1 cholesterol transport was greatly reduced after chlorination by MPO. Loss of activity occurred in concert with chlorination of Tyr(192). Both ONOO(-) and MPO nitrated Tyr(192) in high yield, but unlike chlorination, nitration minimally affected the ability of apoA-I to promote cholesterol efflux from cells. Our results indicate that Tyr(192) is the predominant site of nitration and chlorination when MPO or ONOO(-) oxidizes lipid-free apoA-I but that only chlorination markedly reduces the cholesterol efflux activity of apoA-I. This impaired biological activity of chlorinated apoA-I suggests that MPO-mediated oxidation of HDL might contribute to the link between inflammation and cardiovascular disease.

• Authors: Baohai Shao, Constanze Bergt, Xiaoyun Fu, Pattie Green, John C Voss, Michael N Oda, John F Oram, Jay W Heinecke
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 280 Issue 7 Pg. 5983-93 (Feb 18 2005) ISSN: 0021-9258 [Print] United States
• PMID: 15574409 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• ABCA1 protein, human
• ATP Binding Cassette Transporter 1
• ATP-Binding Cassette Transporters
• Antioxidants
• Apolipoprotein A-I
• Nitrates
• Peptides
• Peroxynitrous Acid
• 3-nitrotyrosine
• Tyrosine
• Chlorine
• Cholesterol
• Hydrogen Peroxide
• Peroxidase
• Nitrogen

Topics

• ATP Binding Cassette Transporter 1
• ATP-Binding Cassette Transporters (genetics, metabolism)
• Amino Acid Sequence
• Animals
• Antioxidants (metabolism, pharmacology)
• Apolipoprotein A-I (chemistry, genetics, metabolism)
• Biological Transport (drug effects)
• Cell Line
• Chlorine (metabolism)
• Cholesterol (metabolism)
• Cricetinae
• Electron Spin Resonance Spectroscopy
• Humans
• Hydrogen Peroxide (metabolism)
• Hydrophobic and Hydrophilic Interactions
• Nitrates (metabolism, pharmacology)
• Nitrogen (metabolism)
• Oxidation-Reduction
• Peptides (chemistry, metabolism)
• Peroxidase (metabolism)
• Peroxynitrous Acid (metabolism, pharmacology)
• Spectrometry, Mass, Electrospray Ionization
• Tyrosine (analogs & derivatives, genetics, metabolism)