Gold L I, Rostagno A, Frangione B, Passalaris T
Department of Pathology, New York University Medical Center, New York 10016.
J Cell Biochem. 1992 Dec;50(4):441-52. doi: 10.1002/jcb.240500412.
Urokinase (u-PA) proteolytically cleaves both human plasma (pFn) and cellular (cFn) dimeric fibronectin (M(r) 440,000) into four major polypeptides of approximately M(r) 210,000, 200,000, 25,000, and 6,000. Amino acid sequence analysis of the polypeptide fragments indicated that the enzymatic cleavage of Fn occurs at two sites: 1) between an arginine/alanine peptide bond located C-terminal to residue 259; this cleavage liberates the N-terminal M(r) 25,000 fragment and the M(r) 210,000 and M(r) 200,000 polypeptides derived from the A and B chains of Fn, respectively; and 2) between an arginine/threonine peptide bond located C-terminal to residue 2,299, thereby yielding an M(r) 6,000 dimeric fragment containing the C-terminal interchain disulfide bonds. Predigestion of Fn with u-PA increased the molecule's vulnerability to further attack by the enzymes plasmin and cathepsin D. These data provide further biochemical evidence for the proteolytic cleavage of fibronectin by plasminogen activators and substantiate that u-PA digestion of Fn may be an initial event in the local degradation of the extracellular matrix by malignant cells, possessing elevated levels of these enzymes.
尿激酶（u-PA）可将人血浆（pFn）和细胞（cFn）中的二聚体纤连蛋白（分子量440,000）蛋白水解切割成四种主要多肽，分子量分别约为210,000、200,000、25,000和6,000。对这些多肽片段的氨基酸序列分析表明，Fn的酶切发生在两个位点：1）位于第259位残基C端的精氨酸/丙氨酸肽键之间；这种切割释放出N端分子量25,000的片段以及分别来自Fn A链和B链的分子量210,000和200,000的多肽；2）位于第2299位残基C端的精氨酸/苏氨酸肽键之间，从而产生一个包含C端链间二硫键的分子量6,000的二聚体片段。用u-PA对Fn进行预消化会增加该分子对纤溶酶和组织蛋白酶D进一步攻击的敏感性。这些数据为纤溶酶原激活剂对纤连蛋白的蛋白水解切割提供了进一步的生化证据，并证实u-PA对Fn的消化可能是恶性细胞局部降解细胞外基质的起始事件，恶性细胞中这些酶的水平升高。
