Sechler J L, Rao H, Cumiskey A M, Vega-Colón I, Smith M S, Murata T, Schwarzbauer J E
Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
J Cell Biol. 2001 Sep 3;154(5):1081-8. doi: 10.1083/jcb.200102034.
Fibronectin (FN) assembly into a fibrillar extracellular matrix is a stepwise process requiring participation from multiple FN domains. Fibril formation is regulated in part by segments within the first seven type III repeats (III1-7). To define the specific function(s) of this region, recombinant FNs (recFNs) containing an overlapping set of deletions were tested for the ability to assemble into fibrils. Surprisingly, recFN lacking type III repeat III1 (FNDeltaIII1), which contains a cryptic FN binding site and has been suggested to be essential for fibril assembly, formed a matrix identical in all respects to a native FN matrix. Similarly, displacement of the cell binding domain in repeats III9-10 to a position close to the NH2-terminal assembly domain, as well as a large deletion spanning repeats III4-7, had no effect on assembly. In contrast, two deletions that included repeat III2, DeltaIII1-2 and DeltaIII2-5, caused significant reductions in fibril elongation, although binding of FN to the cell surface and initiation of assembly still proceeded. Using individual repeats in binding assays, we show that III2 but not III1 contains an FN binding site. Thus, these results pinpoint repeat III2 as an important module for FN-FN interactions during fibril growth.
纤连蛋白（FN）组装成纤维状细胞外基质是一个逐步的过程，需要多个FN结构域的参与。纤维形成部分受前七个III型重复序列（III1 - 7）内的片段调控。为了确定该区域的特定功能，测试了含有一组重叠缺失的重组FN（recFN）组装成纤维的能力。令人惊讶的是，缺乏III型重复序列III1的recFN（FNDeltaIII1），其包含一个隐蔽的FN结合位点且被认为对纤维组装至关重要，形成了在所有方面都与天然FN基质相同的基质。同样，将III9 - 10重复序列中的细胞结合结构域移位到靠近NH2末端组装结构域的位置，以及跨越III4 - 7重复序列的大缺失，对组装没有影响。相比之下，包括重复序列III2的两个缺失，DeltaIII1 - 2和DeltaIII2 - 5，导致纤维伸长显著减少，尽管FN与细胞表面的结合以及组装的起始仍在进行。在结合试验中使用单个重复序列，我们表明III2而非III1含有一个FN结合位点。因此，这些结果指出重复序列III2是纤维生长过程中FN - FN相互作用的一个重要模块。
