Cui L, Carney D F, Hugli T E
Institute of Basic Medical Science, Chinese Academy of Medical Sciences, Beijing.
Protein Sci. 1994 Aug;3(8):1169-77. doi: 10.1002/pro.5560030803.
The anaphylatoxin C5a is a pro-inflammatory factor generated from C5 during complement activation. C5a derived from rat C5 exhibits significantly greater potency compared to C5a from other species. Rat C5a was 25-fold more potent than human C5a for eliciting spasmogenic contraction of guinea pig ileum. Proteolytic removal of the C-terminal arginine of C5a (C5adesArg) reduced spasmogenic potency of rat C5a by only 4-fold compared to a 3,000-fold reduction for human C5adesArg. In addition, rat C5adesArg was 50-fold more potent than human C5adesArg in a guinea pig vascular permeability (in vivo) assay and as a chemotactic factor for human neutrophils. C5a and C5adesArg were purified from zymosan-activated rat serum. Rat C5a, like human C5a, is glycosylated but contains 77 amino acid residues instead of the 74 residues of human C5a. Comparison of the primary structures of rat and human C5a indicated differences at 30 positions including an insert of 3 residues (LLH) in the rat molecule between residue positions 3 and 4 in human C5a. Insertion of residues LLH between Gln-3 and Lys-4 in a recombinant human C5a molecule using site-directed mutagenesis failed to enhance potency. Synthetic C-terminal analogues of rat C5a proved to be measurably more potent than the corresponding human C5a analogues (Ember JA et al., 1993, Protein Sci 2(Suppl 1):159 [Abstr]). We conclude that multiple sequence differences in the C-terminal effector portion and/or elsewhere in rat C5a, but not the LLH insert, account for the significant enhancement in potency of rat C5a over C5a from other species.
过敏毒素C5a是补体激活过程中由C5产生的一种促炎因子。与其他物种的C5a相比，源自大鼠C5的C5a具有显著更高的效力。大鼠C5a在引发豚鼠回肠痉挛性收缩方面比人C5a强25倍。与人类C5adesArg（C5a的C末端精氨酸经蛋白水解去除后的产物）效力降低3000倍相比，大鼠C5adesArg的痉挛效力仅降低4倍。此外，在豚鼠血管通透性（体内）试验中，大鼠C5adesArg作为人中性粒细胞的趋化因子，其效力比人类C5adesArg高50倍。C5a和C5adesArg从酵母聚糖激活的大鼠血清中纯化得到。大鼠C5a与人C5a一样进行了糖基化修饰，但含有77个氨基酸残基，而不是人C5a的74个残基。大鼠和人C5a一级结构的比较表明，两者在30个位置存在差异，包括大鼠分子在人C5a第3和第4位残基之间插入了3个残基（LLH）。使用定点诱变在重组人C5a分子的Gln-3和Lys-4之间插入残基LLH未能提高效力。事实证明，大鼠C5a的合成C末端类似物比相应的人C5a类似物具有更高的效力（Ember JA等人，1993年，《蛋白质科学》2（增刊1）：159 [摘要]）。我们得出结论，大鼠C5a C末端效应部分和/或其他部位的多个序列差异，而非LLH插入，导致了大鼠C5a比其他物种C5a效力显著增强。
