期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1998
卷号：95
期号：26
页码：15753-15757
DOI：10.1073/pnas.95.26.15753
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The type IIA rat brain sodium channel is composed of three subunits: a large pore-forming subunit and two smaller auxiliary subunits, {beta}1 and {beta}2. The {beta} subunits are single membrane-spanning glycoproteins with one Ig-like motif in their extracellular domains. The Ig motif of the {beta}2 subunit has close structural similarity to one of the six Ig motifs in the extracellular domain of the cell adhesion molecule contactin (also called F3 or F11), which binds to the extracellular matrix molecules tenascin-C and tenascin-R. We investigated the binding of the purified sodium channel and the extracellular domain of the {beta}2 subunit to tenascin-C and tenascin-R in vitro. Incubation of purified sodium channels on microtiter plates coated with tenascin-C revealed saturable and specific binding with an apparent Kd of {approx}15 nM. Glutathione S-transferase-tagged fusion proteins containing various segments of tenascin-C and tenascin-R were purified, digested with thrombin to remove the epitope tag, immobilized on microtiter dishes, and tested for their ability to bind purified sodium channel or the epitope-tagged extracellular domain of {beta}2 subunits. Both purified sodium channels and the extracellular domain of the {beta}2 subunit bound specifically to fibronectin type III repeats 1-2, A, B, and 6-8 of tenascin-C and fibronectin type III repeats 1-2 and 6-8 of tenascin-R but not to the epidermal growth factor-like domain or the fibrinogen-like domain of these molecules. The binding of neuronal sodium channels to extracellular matrix molecules such as tenascin-C and tenascin-R may play a crucial role in localizing sodium channels in high density at axon initial segments and nodes of Ranvier or in regulating the activity of immobilized sodium channels in these locations.
