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Open Access Research article

Identification and characterization of Iporin as a novel interaction partner for rab1

Michael Bayer1, Julia Fischer2, Joachim Kremerskothen2, Edith Ossendorf2, Theodoros Matanis2, Magdalena Konczal2, Thomas Weide3 and Angelika Barnekow2*

Author Affiliations

1 UKM Muenster, Albert-Schweitzer-Str. 33, D-48149 Muenster, Germany

2 Department of Experimental Tumorbiology, University of Muenster, Badestr. 9, D-48149 Muenster, Germany

3 Cilian AG, Johann-Krane-Weg 42, D-48149 Muenster, Germany

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BMC Cell Biology 2005, 6:15  doi:10.1186/1471-2121-6-15

Published: 29 March 2005

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

    r
ab
    1
    b
inding 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.

Conclusion

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.