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1: J Biol Chem. 2003 Feb 7;278(6):4322-30. Epub 2002 Nov 21.
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Proteolytic cleavage of the ectodomain of the L1 CAM family member Tractin.

Xu YZ, Ji Y, Zipser B, Jellies J, Johansen KM, Johansen J.

Department of Zoology and Genetics, Iowa State University, Ames 50011, USA.

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 NH(2)- and COOH-terminal cleavage fragments interact with each other and that this interaction provides a means for the NH(2)-terminal fragment to be tethered to the membrane. Furthermore, in S2 cell aggregation assays we show that the NH(2)-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 NH(2)-terminal fragment to S2 cells expressing only the COOH-terminal fragment can functionally restore the adhesive properties of Tractin.

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PMID: 12446717 [PubMed - indexed for MEDLINE]