Sottrup-Jensen L, Gliemann J, Van Leuven F
FEBS Lett. 1986 Sep 1;205(1):20-4. doi: 10.1016/0014-5793(86)80857-2.
Digestion of methylamine-treated alpha 2-macroglobulin (alpha 2M X MA) with catalytic amounts of papain at pH 4.5 has been investigated. Cleavage of Lys(1313)-Glu resulted in two major products, which could be separated by gel chromatography: a large disulfide bridged fragment set nearly the size of intact alpha 2M X MA, and an 18 kDa fragment, constituting the carboxy-terminal domain of alpha 2M. This domain contained the receptor recognition site, exposed as a result of cleavage of the internal beta-cysteinyl-gamma-glutamyl thiol esters in alpha 2M. Compared with alpha 2M-trypsin complex the apparent affinity for binding to rat hepatocyte receptors was 0.1 and 2% at 4 and 37 degrees C, respectively. The receptor-binding domain presumably forms a compact globular beta-barrel-type structure, stable at pH 2.5-9.0. Chemical modification experiments suggest that receptor binding is contributed by a determinant formed by the precise folding of the polypeptide chain.
已研究了在pH 4.5条件下用催化量的木瓜蛋白酶消化甲胺处理的α2-巨球蛋白（α2M X MA）。Lys(1313)-Glu的裂解产生了两种主要产物，可通过凝胶色谱法分离：一个几乎与完整的α2M X MA大小相同的大的二硫键连接片段组，以及一个18 kDa的片段，构成α2M的羧基末端结构域。该结构域包含受体识别位点，由于α2M中内部β-半胱氨酰-γ-谷氨酰硫酯的裂解而暴露。与α2M-胰蛋白酶复合物相比，在4℃和37℃时与大鼠肝细胞受体结合的表观亲和力分别为0.1%和2%。受体结合结构域可能形成紧密的球状β-桶型结构，在pH 2.5-9.0时稳定。化学修饰实验表明，受体结合是由多肽链精确折叠形成的一个决定簇促成的。
