Kerfelec B, Chapus C, Vachette P
Centre de Biochimie et de Biologie Moléculaire du CNRS, Marseille, France.
Eur Biophys J. 1988;16(2):95-100. doi: 10.1007/BF00255518.
Bovine pancreatic procarboxypeptidase A is secreted as a non-covalent association of three different proteins (pro CPA-S6). The free native subunits can be obtained by dissociation of the complex by dimethylmaleylation. Moreover, two specific binary complexes resulting from the high affinity of procarboxypeptidase A (subunit I) for its other two partners (subunits II and III) can also be obtained. In order to better understand the function of the association, an investigation of the morphology of the ternary complex by solution X-ray scattering has been carried out. The radii of gyration of all the molecular species have been obtained and the experimental results have been interpreted in terms of compact objects of simple shape. The various components correspond to globular particles as shown by the value of the ratio Rg/M1/3. This is confirmed by the moderate anisotropy of the simple geometric shapes determined using an assumed value of 0.3 g H2O/g protein for the hydration. The distances between the centres of gravity of pairs of species strongly suggest that the components are in the closest distance configuration or close to it. However, the binary complex I-III appears to be more open than the complex I-II. Finally, a model of the interaction between carboxpeptidase A and its activation peptide has been constructed by comparing the hypothetical geometric model of subunit I to the crystallographically determined structure of carboxypeptidase A.
牛胰羧肽酶原A以三种不同蛋白质的非共价结合形式分泌（pro CPA-S6）。通过二甲基马来酰化使复合物解离可得到游离的天然亚基。此外，还可得到由羧肽酶原A（亚基I）与其另外两个伙伴（亚基II和III）的高亲和力产生的两种特定二元复合物。为了更好地理解这种结合的功能，已通过溶液X射线散射对三元复合物的形态进行了研究。已获得所有分子种类的回转半径，并根据简单形状的致密物体对实验结果进行了解释。如Rg/M1/3比值所示，各种组分对应于球形颗粒。使用0.3 g H2O/g蛋白质的水合假定值确定的简单几何形状的适度各向异性证实了这一点。成对物种重心之间的距离强烈表明各组分处于最接近的距离构型或接近该构型。然而，二元复合物I-III似乎比复合物I-II更开放。最后，通过将亚基I的假设几何模型与羧肽酶A的晶体学确定结构进行比较，构建了羧肽酶A与其激活肽之间相互作用的模型。
