The Molecular Biology Institute, Boyer Hall, Molecular Biology Institute, University of California, Los Angeles, CA, 90095, USA.
Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA, 90095, USA.
Lipids. 2021 May;56(3):269-278. doi: 10.1002/lipd.12286. Epub 2020 Dec 17.
A variety of rodents have been used as experimental animals in metabolic studies of plasma lipids and lipoproteins. These studies have included understanding the functional role of apolipoprotein A-I, the major protein on the surface of HDL. Reviewing the genomic database for entries for rodent apoA-I genes, it was discovered that the naked mole-rat (Heterocephalus glaber) gene encoded a protein with a cysteine at residue 28. Previously, two cases have been reported in which human heterozygotes had apoA-I with cysteine at residues 173 (apoA-I Milano) or at 151 (apoA-I Paris). Interestingly, both groups, in spite of having low levels of HDL and moderately elevated plasma triacylglycerols, had no evidence of cardiovascular disease. Moreover, the presence of the cysteine enabled the apoA-I to form both homodimers and heterodimers. Prior to this report, no other mammalian apoA-I has been found with a cysteine in its sequence. In addition, the encoded naked mole-rat protein had different amino acids at sites that were conserved in all other mammals. These differences resulted in naked mole-rat apoA-I having an unexpected neutral pI value, whereas other mammalian apoA-I have negative pI values. To verify these sequence differences and to determine if the N-terminal location of C28 precluded dimer formation, we conducted mass spectrometry analyses of apoA-I and other proteins associated with HDL. Consistent with the genomic data, our analyses confirmed the presence of C28 and the formation of a homodimer. Analysis of plasma lipids surprisingly revealed a profile similar to the human heterozygotes.
多种啮齿动物已被用于研究血浆脂质和脂蛋白的代谢，其中包括了解载脂蛋白 A-I 的功能作用，载脂蛋白 A-I 是 HDL 表面的主要蛋白。在对啮齿动物载脂蛋白 A-I 基因的基因组数据库进行审查时，发现裸鼹鼠（Heterocephalus glaber）基因编码的蛋白在残基 28 处带有半胱氨酸。此前，有两例人类杂合子载脂蛋白 A-I 在残基 173 处（载脂蛋白 A-I Milano）或在残基 151 处（载脂蛋白 A-I Paris）带有半胱氨酸，已有报道。有趣的是，这两组人群尽管 HDL 水平较低，血浆三酰甘油中度升高，但均无心血管疾病的证据。此外，半胱氨酸的存在使载脂蛋白 A-I 能够形成同源二聚体和异源二聚体。在此报告之前，尚未在其他哺乳动物载脂蛋白 A-I 中发现半胱氨酸。此外，编码的裸鼹鼠蛋白在所有其他哺乳动物都保守的位点上具有不同的氨基酸。这些差异导致裸鼹鼠载脂蛋白 A-I 具有意外的中性 pI 值，而其他哺乳动物载脂蛋白 A-I 具有负 pI 值。为了验证这些序列差异并确定 C28 的 N 端位置是否阻止二聚体形成，我们对载脂蛋白 A-I 及与 HDL 相关的其他蛋白进行了质谱分析。与基因组数据一致，我们的分析证实了 C28 的存在和同源二聚体的形成。对血浆脂质的分析令人惊讶地揭示了与人类杂合子相似的图谱。
