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J. Biol. Chem., Vol. 278, Issue 6, 4322-4330, February 7, 2003

This Article Full Text Full Text (PDF) All Versions of this Article: 278/6/4322    most recent M210775200v1 Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Xu, Y.-Z. Articles by Johansen, J. Search for Related Content PubMed PubMed Citation Articles by Xu, Y.-Z. Articles by Johansen, J. Social Bookmarking                      What's this?

Proteolytic Cleavage of the Ectodomain of the L1 CAM Family Member Tractin^*

Ying-Zhi Xu, Yun Ji, Birgit Zipser, John Jellies^§, Kristen M. Johansen, and Jørgen Johansen^¶

From the Department of Zoology and Genetics, Iowa State University, Ames, Iowa 50011, the ^§ Department of Biological Sciences, Western Michigan University, Kalamazoo, Michigan 49008, and the  Department of Physiology, Michigan State University, East Lansing, Michigan 48824

Tractin is a member of the L1 family of cell adhesion molecules in leech. Immunoblot analysis suggests that Tractin is constitutively cleaved in vivo at a proteolytic site with the sequence RKRRSR. This sequence conforms to the consensus sequence for cleavage by members of the furin family of convertases, and this proteolytic site is shared by a majority of other L1 family members. We provide evidence with furin-specific inhibitor experiments, by site-specific mutagenesis of Tractin constructs expressed in S2 cells, as well as by Tractin expression in furin-deficient LoVo cells that a furin convertase is the likely protease mediating this processing. Cross-immunoprecipitations with Tractin domain-specific antibodies suggest that the resulting NH₂- and COOH-terminal cleavage fragments interact with each other and that this interaction provides a means for the NH₂-terminal fragment to be tethered to the membrane. Furthermore, in S2 cell aggregation assays we show that the NH₂-terminal fragment is necessary for homophilic adhesion and that cells expressing only the transmembrane COOH-terminal fragment are non-adhesive. However, tethering of exogeneously provided Tractin NH₂-terminal fragment to S2 cells expressing only the COOH-terminal fragment can functionally restore the adhesive properties of Tractin.

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