Identification of sites in apolipoprotein A-I susceptible to chymase and carboxypeptidase A digestion.
MCs (mast cells) adversely affect atherosclerosis by promoting the progression of lesions and plaque destabilization. MC chymase cleaves apoA-I (apolipoprotein A-I), the main protein component of HDL (high-density lipoprotein). We previously showed that C-terminally truncated apoA-I (cleaved at the carboxyl side of Phe(225)) is present in normal human serum using a newly developed specific mAb (monoclonal antibody). In the present study, we aimed to identify chymase-induced cleavage sites in both lipid-free and lipid-bound (HDL(3)) forms of apoA-I. Lipid-free apoA-I was preferentially digested by chymase, at the C-terminus rather than the N-terminus. Phe(229) and Tyr(192) residues were the main cleavage sites. Interestingly, the Phe(225) residue was a minor cleavage site. In contrast, the same concentration of chymase failed to digest apoA-I in HDL(3); however, a 100-fold higher concentration of chymase modestly digested apoA-I in HDL(3) at only the N-terminus, especially at Phe(33). CPA (carboxypeptidase A) is another MC protease, co-localized with chymase in severe atherosclerotic lesions. CPA, in vitro, further cleaved C-terminal Phe(225) and Phe(229) residues newly exposed by chymase, but did not cleave Tyr(192). These results indicate that several forms of C-terminally and N-terminally truncated apoA-I could exist in the circulation. They may be useful as new biomarkers to assess the risk of CVD (cardiovascular disease).
Analytical Laboratory Chemistry, Graduate School of Health Care Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Tokyo 113-8519, Japan.
Yoko
Y
Usami
Yukihiro
Y
Kobayashi
Takahiro
T
Kameda
Akari
A
Miyazaki
Kazuyuki
K
Matsuda
Mitsutoshi
M
Sugano
Kenji
K
Kawasaki
Yuriko
Y
Kurihara
Takeshi
T
Kasama
Minoru
M
Tozuka
D001013:Aorta, Thoracic / Q000737:chemistry / Q000473:pathology; D016632:Apolipoprotein A-I / Q000097:blood / Q000737:chemistry*; D015415:Biomarkers / Q000097:blood; D043422:Carboxypeptidases A / Q000737:chemistry*; D020134:Catalytic Domain; D053818:Chymases / Q000737:chemistry*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007150:Immunohistochemistry; D053440:Lipoproteins, HDL3 / Q000097:blood / Q000737:chemistry; D010649:Phenylalanine / Q000737:chemistry; D058226:Plaque, Atherosclerotic / Q000737:chemistry / Q000473:pathology; D059748:Proteolysis; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014443:Tyrosine / Q000737:chemistry
C505693:APOA1 protein, human; D016632:Apolipoprotein A-I; D015415:Biomarkers; D053440:Lipoproteins, HDL3; D014443:Tyrosine; D010649:Phenylalanine; D043422:Carboxypeptidases A; D053818:Chymases