Novokhatny V V, Kudinov S A, Privalov P L
J Mol Biol. 1984 Oct 25;179(2):215-32. doi: 10.1016/0022-2836(84)90466-2.
Calorimetric studies of intramolecular melting of human plasminogen and of its fragments under various solvent conditions show that the intact plasminogen molecule consists of seven compact co-operative subunits, which can be regarded as structural domains. Five of these domains are formed by the homologous regions, the kringles, two domains are formed by the C-terminal part of the polypeptide chain that is split at activation, forming the light chain in plasmin, while the initial 76 amino acid residue peptide does not form any compact co-operative structure. The specific influence of epsilon-aminocaproic acid on the stability of the first, the fourth and, to a lesser extent, on the second kringle domain, provides evidence that these three domains in plasminogen possess lysine-binding ability. The first four kringle domains are almost independent in the molecule, while the fifth interacts with that part of the light chain not included in either of the two domains of this chain. These two domains are of different size and co-operate strongly in plasminogen, but at its activation into plasmin they decooperate and the stability of the smaller domain, which is formed by the N-terminal part of the light chain, decreases significantly. Since the light chain is responsible for the proteolytic activity of plasmin, it becomes clear that the active site of this protein is composed of two domains, as is the case for other serine proteases.
在各种溶剂条件下对人纤溶酶原及其片段的分子内解链进行的量热研究表明，完整的纤溶酶原分子由七个紧密协作的亚基组成，这些亚基可被视为结构域。其中五个结构域由同源区域（kringles）形成，两个结构域由多肽链的C端部分形成，该部分在激活时被切割，在纤溶酶中形成轻链，而最初的76个氨基酸残基肽不形成任何紧密协作的结构。ε-氨基己酸对第一个、第四个以及在较小程度上对第二个kringle结构域稳定性的特定影响，证明纤溶酶原中的这三个结构域具有赖氨酸结合能力。前四个kringle结构域在分子中几乎是独立的，而第五个结构域与轻链两个结构域之外的轻链部分相互作用。这两个结构域大小不同，在纤溶酶原中强烈协作，但在其激活为纤溶酶时它们失去协作，由轻链N端部分形成的较小结构域的稳定性显著降低。由于轻链负责纤溶酶的蛋白水解活性，显然该蛋白的活性位点由两个结构域组成，其他丝氨酸蛋白酶也是如此。
