The multi-domain adaptor protein Intersectin is involved in several signal transduction pathways in the cell. It interacts with various components of the endocytic pathway and plays an important role in regulation of Ras induced activation of MAPK kinases and other GTPase regulated processes. The human gene for Intersectin 1 is located in the Down Syndrome region of chromosome 21 (Pucharcos et al., 1999).
Intersectin is a multidomain adaptor protein and combines different protein-protein interaction modules (fig 1). At the N-terminus Intersectin exhibits two Eps15 homology domains that are found in proteins of the endocytic pathway. EH domains are evolutionary conserved protein interaction domains with a number of cellular ligands. Via these domains it binds a specific motif- the NPF (asparagin, proline, phenylalanin)-motif in other endocytic proteins like Epsin or Synaptojanin (Santolini et al., 1999).
The coiled-coil domain of Intersectin is supposed to be responsible for the formation of homodimers and heterodimers with Eps15 (Santolini et al., 1999).
Intersectin contains 5 SH3-domains that bind proline-rich stretches within other proteins. Using for example immunoprecipitation assays and GST-pulldown experiments many binding partners for these SH3 domains were identified (Yamabhai et al., 1998; Sengar et al., 1999; Roos and Kelly, 1998; Tong et al., 2000; Adams et al., 2000). Among them are endocytic proteins like dynamin or synaptojanin and proteins involved in other signaling pathways such as mSos, an exchange factor for Ras and N-WASP, a regulator of actin polymerization.
Intersectin as nucleotide exchange factor
A longer splicing variant of Intersectin additionally carries a Dbl homology (DH), Pleckstrin homology (PH) and C2-domain. DH domains catalyze the nucleotide exchange for the family of Rho GTPases and are usually found adjacent to PH domains, which bind phospholipids and thus could be responsible for membrane anchoring of the exchange factors. A not fully understood aspect of GEF function is the regulation of GEF activity. Given that GEFs are mostly multi-domain proteins, one important issue is in how far neighboring domains are involved in modulating GEF activity. As Intersectin was shown to be inhibited in its full-length, we characterized the autoinhibitory mechanism in order to identify domains or motives involved. Furthermore, binding of N-WASP to Intersectin was proposed to relieve this autoinhibition (Hussain et al., 2001), we analyzed the interaction between these proteins and its effect on GEF activity (Kintscher et al., 2010).
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Hussain, N.K., Jenna, S., Glogauer, M., Quinn, C.C., Wasiak, S., Guipponi, M., Antonarakis, S.E., Kay, B.K., Stossel, T.P., Lamarche-Vane, N., et al. (2001). Endocytic protein intersectin-l regulates actin assembly via Cdc42 and N-WASP. Nat Cell Biol 3, 927-932.
Kintscher, C., Wuertenberger, S., Eylenstein, R., Uhlendorf, T., and Groemping, Y. (2010). Autoinhibition of GEF activity in intersectin 1 is mediated by the short SH3-DH domain linker. Protein Sci.
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