Role of glutamic acid residues 154, 155, and 165 of lecithin:cholesterol acyltransferase in cholesterol esterification and phospholipase A2 activities

Wang, Jingchuan; DeLozier, Jeanine A.; Gebre, Abraham K.; Dolphin, Peter J.; Parks, John S.

doi:10.1016/s0022-2275(20)34202-4

Cited by 5 publications

(2 citation statements)

References 25 publications

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“…Positively charged residues present in both helices 144 -165 and 166-186 may interact with negatively charged residues found on this LCAT helix. Mutagenesis studies of LCAT by Wang et al (164) have shown that Glu 154, 155, and 165 are not important for LCAT activity but may be involved in the binding of cholesterol. The region 151 -174 of LCAT may therefore indirectly interact with apoA-I through the binding with HDL cholesterol, a process that may result in a conformational change of LCAT and its activation.…”

Section: B Apoa-i Mutants and Identification Of Domains Involved In Lcat Activationmentioning

confidence: 99%

Apolipoprotein A-I: structure–function relationships

Frank

Marcel

2000

Journal of Lipid Research

266

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The inverse relationship between high density lipoprotein (HDL) plasma levels and coronary heart disease has been attributed to the role that HDL and its major constituent, apolipoprotein A-I (apoA-I), play in reverse cholesterol transport (RCT). The efficiency of RCT depends on the specific ability of apoA-I to promote cellular cholesterol efflux, bind lipids, activate lecithin:cholesterol acyltransferase (LCAT), and form mature HDL that interact with specific receptors and lipid transfer proteins. From the intensive analysis of apoA-I secondary structure has emerged our current understanding of its different classes of amphipathic ␣ -helices, which control lipid-binding specificity. The main challenge now is to define apoA-I tertiary structure in its lipid-free and lipid-bound forms. Two models are considered for discoidal lipoproteins formed by association of two apoA-I with phospholipids. In the first or picket fence model, each apoA-I wraps around the disc with antiparallel adjacent ␣ -helices and with little intermolecular interactions. In the second or belt model, two antiparallel apoA-I are paired by their C-terminal ␣ -helices, wrap around the lipoprotein, and are stabilized by multiple intermolecular interactions. While recent evidence supports the belt model, other models, including hybrid models, cannot be excluded. ApoA-I ␣ -helices control lipid binding and association with varying levels of lipids. The N-terminal helix 44-65 and the C-terminal helix 210-241 are recognized as important for the initial association with lipids. In the central domain, helix 100-121 and, to a lesser extent, helix 122-143, are also very important for lipid binding and the formation of mature HDL, whereas helices between residues 144 and 186 contribute little. The LCAT activation domain has now been clearly assigned to helix 144-165 with secondary contribution by helix 166-186. The lower lipid binding affinity of the region 144-186 may be important to the activation mechanism allowing displacement of these apoA-I helices by LCAT and presentation of the lipid substrates.No specific sequence has been found that affects diffusional efflux to lipid-bound apoA-I. In contrast, the C-terminal helices, known to be important for lipid binding and maintenance of HDL in circulation, are also involved in the interaction of lipid-free apoA-I with macrophages and specific lipid efflux. While much progress has been made, other aspects of apoA-I structure-function relationships still need to be studied, particularly its lipoprotein topology and its interaction with other enzymes, lipid transfer proteins and receptors important for HDL metabolism. -Frank, P. G., and Y. L. Marcel. Apolipoprotein A-I: structure-function relationships.

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Section: B Apoa-i Mutants and Identification Of Domains Involved In Lcat Activationmentioning

confidence: 99%

Apolipoprotein A-I: structure–function relationships

Frank

Marcel

2000

Journal of Lipid Research

266

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“…Moreover, even different synthetic amphipathic peptides and CNBr fragments of apoA-I have been able to activate LCAT with varying efficiencies (45). In support of this concept, it has recently been suggested that salt bridge formation between positive charges in LCAT and negative charges in the amphipathic helices of apoA-I are directly involved in the activation of the enzyme (46). Thus, it is possible that only much stronger modifications of HDL, such as those causing high MW cross-linked forms of apoA-I and apoA-II, would cause inhibition of LCAT activity (47).…”

Section: Discussionmentioning

confidence: 95%

Identification of domains in apoA-I susceptible to proteolysis by mast cell chymase: implications for HDL function

Lee

Uboldi

Giudice

et al. 2000

Journal of Lipid Research

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When stimulated, rat serosal mast cells degranulate and secrete a cytoplasmic neutral protease, chymase. We studied the fragmentation of apolipoprotein (apo) A-I during proteolysis of HDL 3 by chymase, and examined how chymase-dependent proteolysis interfered with the binding of eight murine monoclonal antibodies (Mabs) against functional domains of apoA-I. Size exclusion chromatography of HDL 3 revealed that proteolysis for up to 24 h did not alter the integrity of the ␣ -migrating HDL, whereas a minor peak containing particles of smaller size with pre ␤ mobility disappeared after as little as 15 min of incubation. At the same time, generation of a large (26 kDa) polypeptide containing the N-terminus of apoA-I was detected. This large fragment and other medium-sized fragments of apoA-I produced after prolonged treatment with chymase were found to be associated with the ␣ HDL; meanwhile, small lipid-free peptides were rapidly produced. Incubation of HDL 3 with chymase inhibited binding of Mab A-I-9 (specific for pre ␤ 1 HDL) most rapidly (within 15 min) of the eight studied Mabs. This rapid loss of binding was paralleled by a similar reduction in the ability of HDL 3 to induce high-affinity efflux of cholesterol from macrophage foam cells, indicating that proteolysis had destroyed an epitope that is critical for this function. In sharp contrast, prolonged degradation of HDL 3 by chymase failed to reduce the ability of HDL 3 to activate LCAT, even though it led to modification of three epitopes in the central region of apoA-I that are involved in lecithin cholesterol acyltransferase (LCAT) activation. This differential sensitivity of the two key functions of HDL 3 to the proteolytic action of mast cell chymase is compatible with the notion that, in reverse cholesterol transport, intactness of apoA-I is essential for pre ␤ 1 HDL to promote the high-affinity efflux of cellular cholesterol, but not for the ␣ -migrating HDL particles to activate LCAT. -Lee, M., P. Uboldi, D. Giudice, A. L. Catapano, and P. T. Kovanen. Identification of domains in apoA-I susceptible to proteolysis by mast cell chymase: implications for HDL function. J. Lipid Res. 41: 975-984.Supplementary key words ␣ -and pre ␤ -migrating HDL • monoclonal antibodies • LCAT • cellular cholesterol efflux • proteolysis of apoA-I

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