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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2008;28:2063.)
© 2008 American Heart Association, Inc.

Cell Biology/Signaling

Apolipoprotein A-I Tryptophan Substitution Leads to Resistance to Myeloperoxidase-Mediated Loss of Function

Dao-Quan Peng; Gregory Brubaker; Zhiping Wu; Lemin Zheng; Belinda Willard; Michael Kinter; Stanley L. Hazen; Jonathan D. Smith

From the Department of Cell Biology, Cleveland Clinic, Cleveland Ohio. Current address for D.-Q.P.: Department of Cardiology, The Second Xiangya Hospital, Central South University, Changsha, Hunan 410011 China.

Correspondence to Jonathan D. Smith, Department of Cell Biology, NC10, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195. E-mail smithj4{at}ccf.org

Objective— Apolipoprotein A-I (apoAI) acts as an ABCA1-dependent acceptor of cellular phospholipids and cholesterol during the biogenesis of HDL, but this activity is susceptible to oxidative inactivation by myeloperoxidase. We tried to determine which residues mediated this inactivation and create an oxidant-resistant apoAI variant.

Methods and Results— Mass spectrometry detected the presence of tryptophan, methionine, tyrosine, and lysine oxidation in apoAI recovered from human atheroma. We investigated the role of these residues in the myeloperoxidase-mediated loss of apoAI activity. Site-directed mutagenesis and chemical modification were used to create variants of apoAI which were tested for ABCA1-dependent cholesterol acceptor activity and oxidative inactivation. We previously reported that tyrosine modification is not required for myeloperoxidase-induced loss of apoAI function. Lysine methylation did not alter the sensitivity of apoAI to myeloperoxidase, whereas site-specific substitution of apoAI methionine to valine increased the sensitivity of apoAI to myeloperoxidase. ApoAI tryptophan residues were identified as essential in apoAI function and oxidant sensitivity as substitution of all four apoAI tryptophan residues to leucine led to loss of function, but the conservative substitution to phenylalanine retained full function and was resistant to oxidative inactivation.

Conclusions— Tryptophan modification of apoAI is primarily responsible for the myeloperoxidase-mediated loss of the cholesterol acceptor activity of apoAI.

Key Words: dysfunctional HDL • oxidation • atherosclerosis

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