Karp D R, Capra J D, Atkinson J P, Shreffler D C
J Immunol. 1982 May;128(5):2336-41.
The properties of a 128,000-dalton polypeptide, corresponding to the uncleaved alpha- and gamma- chains of the fourth component of murine complement (C4), were studied. A fragment of similar size (137,000 daltons) from the structurally related sex-limited protein (Slp) was also found. These polypeptides have methylamine and iodoacetamide binding sites. suggesting that they, like the alpha-chains of C4 and Slp, possess an internal thiolester. In tryptic peptide map analysis, extensive homology is seen between the 128,000-dalton fragment and native C4 alpha- and gamma-chains. N-terminal sequences for this fragment and C4 alpha are identical, as are those for the 137,000-dalton Slp fragment and Slp alpha. Although the alpha-gamma fragment, like C4 alpha, undergoes denaturation-dependent autolytic cleavage, unlike C4 alpha, it cannot be cleaved by C1 This indicate that some of the properties of C4 do not require the native three-chain structure, whereas others do require it. These findings suggest that the alpha-gamma fragments represent an intermediate step in the processing of the C4 and Slp precursor polypeptides.
对一种128,000道尔顿多肽的特性进行了研究，该多肽对应于小鼠补体第四成分（C4）未裂解的α链和γ链。还发现了来自结构相关的性限制蛋白（Slp）的类似大小（137,000道尔顿）的片段。这些多肽具有甲胺和碘乙酰胺结合位点，表明它们与C4和Slp的α链一样，拥有一个内部硫酯键。在胰蛋白酶肽图谱分析中，128,000道尔顿片段与天然C4α链和γ链之间存在广泛的同源性。该片段和C4α的N端序列相同，137,000道尔顿的Slp片段和Slpα的N端序列也相同。虽然α-γ片段像C4α一样会发生依赖变性的自溶裂解，但与C4α不同的是，它不能被C1裂解。这表明C4的一些特性不需要天然的三链结构，而其他特性则需要。这些发现表明，α-γ片段代表了C4和Slp前体多肽加工过程中的一个中间步骤。
