Porteu F, Halbwachs-Mecarelli L
Institut National de la Santé et de la Recherche Médicale U25, Hôpital Necker, Paris, France.
J Biol Chem. 1988 Apr 15;263(11):5091-7.
The binding of highly purified monomeric 125I-C3b to its receptor (CR1) on resting human polymorphonuclear neutrophils (PMN) was analyzed under equilibrium conditions, at 4 degrees C and low ionic strength. Scatchard analysis of specific binding data yielded curvilinear concave upward plots, which resulted from the presence of site-site interactions of the negative type among PMN C3b-receptors (negative cooperativity), as shown by dissociation kinetic experiments. Indeed, the dissociation rate of 125I-C3b from PMN was markedly increased in the presence of an excess of unlabeled C3b in the dilution medium and was directly dependent on the degree of initial receptor occupancy with the radioligand. These interactions occurred when 2% of the receptors were occupied with 125I-C3b and resulted in a 4-fold decrease in CR1 affinity when the receptor went from its "empty" to its "filled" conformation. In a disease associated with a continuous production of C3b (factor I deficiency), CR1 on in vivo circulating PMN was found to be in a "low affinity" and "high dissociating" state similar to that of normal CR1 at high occupancy. Finally, negative cooperativity among CR1 sites disappeared after PMN activation with chemotactic peptides.
在4℃和低离子强度的平衡条件下，分析了高纯度单体125I-C3b与其在静息人多形核中性粒细胞（PMN）上的受体（CR1）的结合情况。对特异性结合数据的Scatchard分析产生了向上凹的曲线，这是由于PMN C3b受体之间存在负性位点-位点相互作用（负协同性）所致，解离动力学实验表明了这一点。实际上，在稀释介质中存在过量未标记的C3b时，125I-C3b从PMN的解离速率显著增加，并且直接取决于放射性配体对初始受体的占据程度。当2%的受体被125I-C3b占据时就会发生这些相互作用，当受体从“空”构象转变为“满”构象时，CR1亲和力会降低4倍。在与C3b持续产生相关的疾病（因子I缺乏症）中，发现体内循环PMN上的CR1处于“低亲和力”和“高解离”状态，类似于正常CR1在高占据时的状态。最后，在用趋化肽激活PMN后，CR1位点之间的负协同性消失。
