Francis C W, Müller E, Henschen A, Simpson P J, Marder V J
Department of Medicine, University of Rochester School of Medicine and Dentistry, NY 14642.
Proc Natl Acad Sci U S A. 1988 May;85(10):3358-62. doi: 10.1073/pnas.85.10.3358.
The gamma chain of human fibrinogen has been shown to be heterogeneous; three forms of various sizes are normally present in plasma. To further characterize the two less prevalent elongated variants, we have purified the three forms of the gamma chain, isolated unique tryptic fragments, and sequenced the variant portions of each chain. The intermediate-sized form (gamma 55) has a sequence identical to the longest variant (gamma 57.5) from residue Val-408 to Pro-423, which is the C terminus of the gamma 55 chain. The gamma 57.5 chain extends an additional four amino acids. The C-terminal amino acid sequence and corresponding nucleotide sequence of the gamma 55 chain show marked similarity with an elongated gamma-chain variant of rat fibrinogen. In addition, a remarkable similarity in both amino acid and nucleotide sequence was noted between the human gamma 55 chain and the C-terminal extension in human and bovine A alpha chain of fibrinogen, which are encoded by the cDNA but are posttranslationally cleaved and are not found in plasma. The findings suggest an evolutionary conservation in the C-terminal amino acid sequence found in both the fibrinogen A alpha and gamma chains in several species.
人纤维蛋白原的γ链已被证明具有异质性；血浆中通常存在三种不同大小的形式。为了进一步表征两种不太常见的延长变体，我们纯化了γ链的三种形式，分离出独特的胰蛋白酶片段，并对每条链的变体部分进行了测序。中等大小的形式（γ55）从残基Val-408到Pro-423的序列与最长变体（γ57.5）相同，这是γ55链的C末端。γ57.5链又延伸了四个氨基酸。γ55链的C末端氨基酸序列和相应的核苷酸序列与大鼠纤维蛋白原的延长γ链变体显示出显著的相似性。此外，在人γ55链与人及牛纤维蛋白原Aα链的C末端延伸之间，在氨基酸和核苷酸序列上都观察到了显著的相似性，它们由cDNA编码，但在翻译后被切割，在血浆中不存在。这些发现表明，在几种物种的纤维蛋白原Aα和γ链中发现的C末端氨基酸序列存在进化保守性。
