Pontes M, Xu X, Graham D, Riley M, Doolittle R F
Biochemistry. 1987 Mar 24;26(6):1611-7. doi: 10.1021/bi00380a019.
The messages for two small but abundant apolipoproteins found in lamprey blood plasma were cloned with the aid of oligonucleotide probes based on amino-terminal sequences. In both cases, numerous clones were identified in a lamprey liver cDNA library, consistent with the great abundance of these proteins in lamprey blood. One of the cDNAs (LAL1) has a coding region of 105 amino acids that corresponds to a 21-residue signal peptide, a putative 8-residue propeptide, and the 76-residue mature protein found in blood. The other cDNA (LAL2) codes for a total of 191 residues, the first 23 of which constitute a signal peptide. The two proteins, which occur in the "high-density lipoprotein fraction" of ultracentrifuged plasma, have amino acid compositions similar to those of apolipoproteins found in mammalian blood; computer analysis indicates that the sequences are largely helix-permissive. When the sequences were searched against an amino acid sequence data base, rat apolipoprotein IV was the best matching candidate in both cases. Although a reasonable alignment can be made with that sequence and LAL1, definitive assignment of the two lamprey proteins to typical mammalian classes cannot be made at this point.
借助基于氨基末端序列的寡核苷酸探针，克隆了在七鳃鳗血浆中发现的两种含量少但丰富的载脂蛋白的信息。在这两种情况下，在七鳃鳗肝脏cDNA文库中都鉴定出了许多克隆，这与这些蛋白质在七鳃鳗血液中的高丰度一致。其中一个cDNA（LAL1）的编码区有105个氨基酸，对应于一个21个残基的信号肽、一个推定的8个残基的前肽以及在血液中发现的76个残基的成熟蛋白。另一个cDNA（LAL2）总共编码191个残基，其中前23个构成信号肽。这两种蛋白质存在于超速离心血浆的“高密度脂蛋白部分”，其氨基酸组成与在哺乳动物血液中发现的载脂蛋白相似；计算机分析表明，这些序列在很大程度上允许形成螺旋结构。当将这些序列与氨基酸序列数据库进行比对时，大鼠载脂蛋白IV在这两种情况下都是最佳匹配候选物。尽管可以将该序列与LAL1进行合理比对，但目前还无法将这两种七鳃鳗蛋白质明确归类到典型的哺乳动物类别中。
