Pariser H P, Rakeman A S, Hausman R E
Department of Biology, Boston University, 5 Cummington Street, Boston, MA 02215, USA.
Brain Res Dev Brain Res. 1998 Nov 1;111(1):1-9. doi: 10.1016/s0165-3806(98)00113-8.
Retina cognin (R-cognin) is a 50-kDa protein on the surface of embryonic chick retina cells that mediates cell-cell recognition and neuronal differentiation. It is developmental stage- and tissue-specific in its expression. The partial cDNA clone for R-cognin is nearly identical to that of chicken protein disulfide isomerase (chicken PDI) and enzyme with thioreductase activity. The R-cognin clone extends from beyond the 3' polyadenylation site up to the boundary between PDI exons 1 and 2, with the putative R-cognin equivalent of PDI exon 1 remaining uncloned. The question posed here was whether the sequence-specific properties of PDI were significant in the action of R-cognin. We show that R-cognin, like PDI, has thioreductase activity as revealed by RNase renaturation enzymatic assays. We then asked if this thioreductase activity was involved in the mediation of cell adhesion and recognition in developing chick retina. We show, through cell aggregation assays, that both R-cognin and chicken PDI enhance chick retina cell aggregation but not that of cells from other CNS tissues. We also show that treating R-cognin and chicken PDI with the thioreductase inhibitor 5,5'-dithio-bis (2-nitrobenzoic acid), which covalently binds to the functional cysteines of the thioreductase active sites, reduces the enhancement of cell aggregation. Thus R-cognin acts, in part, by catalyzing a covalent protein-protein linkage at the cell surface.
视网膜认知蛋白（R - 认知蛋白）是胚胎期鸡视网膜细胞表面一种50千道尔顿的蛋白质，它介导细胞间识别和神经元分化。其表达具有发育阶段和组织特异性。R - 认知蛋白的部分cDNA克隆与鸡蛋白二硫键异构酶（鸡PDI，一种具有硫还原酶活性的酶）的克隆几乎相同。R - 认知蛋白克隆从3'多聚腺苷酸化位点之外延伸至PDI外显子1和2之间的边界，而与PDI外显子1等效的假定R - 认知蛋白部分仍未克隆。这里提出的问题是，PDI的序列特异性特性在R - 认知蛋白的作用中是否重要。我们通过核糖核酸酶复性酶促试验表明，R - 认知蛋白与PDI一样具有硫还原酶活性。然后我们询问这种硫还原酶活性是否参与发育中的鸡视网膜细胞黏附和识别的介导过程。通过细胞聚集试验，我们表明R - 认知蛋白和鸡PDI都能增强鸡视网膜细胞聚集，但对其他中枢神经系统组织的细胞聚集无增强作用。我们还表明，用硫还原酶抑制剂5,5'-二硫代双（2 - 硝基苯甲酸）处理R - 认知蛋白和鸡PDI，该抑制剂与硫还原酶活性位点的功能性半胱氨酸共价结合，会降低细胞聚集的增强作用。因此，R - 认知蛋白部分地通过催化细胞表面的共价蛋白质 - 蛋白质连接起作用。
