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Originally published In Press as doi:10.1074/jbc.M205101200 on June 24, 2002
J. Biol. Chem., Vol. 277, Issue 36, 32722-32729, September 6, 2002
Mammalian Suppressor of Sec4 Modulates the Inhibitory Effect of
Rab15 during Early Endocytosis*
David J.
Strick,
Dina M.
Francescutti,
Yali
Zhao, and
Lisa
A.
Elferink
From the Department of Physiology and Biophysics, Marine Biomedical
Institute, University of Texas Medical Branch,
Galveston, Texas 77555-1069
Rab15 is a novel endocytic Rab that counters the
stimulatory effect of Rab5-GTP on early endocytic trafficking. Rab15
may interfere with Rab5 function directly by sequestering Rab5
effectors or indirectly through novel sets of effector interactions. To distinguish between these possibilities, we examined the effector binding properties of Rab15. Rab15 does not interact directly with the
Rab5 effectors rabex-5 and rabaptin-5 in a yeast two-hybrid binding
assay. Rather mammalian suppressor of Sec4 (Mss4) was identified as a
binding partner for Rab15. Mss4 preferentially binds GDP-bound (T22N)
and nucleotide-free (N121I) Rab15, consistent with the proposed role of
Mss4 as a chaperone that stabilizes target Rabs in their
nucleotide-free form. Mutational analysis of Rab15 indicates that
lysine at position 48 (K48Q) is important for the binding of Rab15-GDP
to Mss4. Moreover, the mutation K48Q counters the inhibitory phenotype
of wild type Rab15 on receptor-mediated endocytosis in HeLa cells and
homotypic endosome fusion in vitro without altering the
relative amount of cell surface-associated transferrin receptor.
Together, these data indicate a novel role for Mss4 as an effector for
Rab15 in early endocytic trafficking.
*
This work was supported in part by National Science
Foundation Grant IBN-9974517 (to L. A. E.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be addressed. Tel.: 409-772-1942;
Fax: 409-772-2789; E-mail: Lisa.Elferink@utmb.edu.
Copyright © 2002 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 2002 by the American Society for Biochemistry and Molecular Biology.
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