title: Identification and characterization of Iporin as a novel interaction partner for rab1.
abstract: BACKGROUND
  The small GTPase rab1a and its isoform rab1b are essential regulating components in the vesicle transport between the ER and the Golgi apparatus. Rab1 is thought to act as a molecular switch and can change between an active GTP-bound and an inactive GDP-bound conformation. To elucidate the function of rab1, several approaches have been established to isolate effector proteins, which interact with the activated conformation of rab1. To date p115, GM130, golgin-84 and MICAL have been identified as direct interacting partners. Together with rab1, these molecules are components of a protein complex, which mediates and regulates intracellular vesicle transport.
  
  
  RESULTS
  Here, we report the characterization of Iporin, which is similar to KIAA0375 as a novel rab1-interacting protein. It was initially identified by yeast two-hybrid screening experiments with the active mutant of rab1b (rab1b Q67R) as bait. Iporin contains a SH3 domain and two polyproline stretches, which are known to play a role in protein/protein interactions. In addition, Iporin encloses a RUN domain, which seems to be a major part of the rab1binding domain (R1BD). Iporin is ubiquitously expressed and immunofluorescence staining displays a cytosolic punctual distribution. Interestingly, we also show that Iporin interacts with another rab1 interacting partner, the GM130 protein.
  
  
  CONCLUSIONS
  Our results demonstrate that Iporin is a potential new interacting partner of rab1. Iporin is different from already identified rab1 interacting proteins concerning protein structure and cellular localization. We conclude that Iporin might function as a link between the targeting of ER derived vesicles, triggered by the rab1 GTPase and a signaling pathway regulated by molecules containing SH3 and/or poly-proline regions. The characterization of this novel intermolecular relation could help to elucidate how vesicles find their way from ER to the Golgi apparatus.
authors.affiliation: UKM Muenster, Albert-Schweitzer-Str. 33, D-48149 Muenster, Germany. bayerm@uni-muenster.de
authors.forename: Michael
authors.initials: M
authors.lastname: Bayer
authors.forename: Julia
authors.initials: J
authors.lastname: Fischer
authors.forename: Joachim
authors.initials: J
authors.lastname: Kremerskothen
authors.forename: Edith
authors.initials: E
authors.lastname: Ossendorf
authors.forename: Theodoros
authors.initials: T
authors.lastname: Matanis
authors.forename: Magdalena
authors.initials: M
authors.lastname: Konczal
authors.forename: Thomas
authors.initials: T
authors.lastname: Weide
authors.forename: Angelika
authors.initials: A
authors.lastname: Barnekow
mesh_terms: D001324:Autoantigens; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D003600:Cytosol; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D010455:Peptides; D011485:Protein Binding; D014018:Tissue Distribution; D020798:Two-Hybrid System Techniques; D020761:rab1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018909:src Homology Domains
chemical_list: D001324:Autoantigens; D002352:Carrier Proteins; C097741:Golgin subfamily A member 2; D008565:Membrane Proteins; D010455:Peptides; C509346:RUSC2 protein, human; C011083:polyproline; D020761:rab1 GTP-Binding Proteins