Journal of Biological Chemistry
Volume 286, Issue 38, 23 September 2011, Pages 33213-33222
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Cell Biology
RUTBC1 Protein, a Rab9A Effector That Activates GTP Hydrolysis by Rab32 and Rab33B Proteins

https://doi.org/10.1074/jbc.M111.261115Get rights and content
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Rab GTPases regulate all steps of membrane trafficking. Their interconversion between active, GTP-bound states and inactive, GDP-bound states is regulated by guanine nucleotide exchange factors and GTPase-activating proteins. The substrates for most Rab GTPase-activating proteins (GAPs) are unknown. Rab9A and its effectors regulate transport of mannose 6-phosphate receptors from late endosomes to the trans-Golgi network. We show here that RUTBC1 is a Tre2/Bub2/Cdc16 domain-containing protein that binds to Rab9A-GTP both in vitro and in cultured cells, but is not a GTPase-activating protein for Rab9A. Biochemical screening of RUTBC1 Rab protein substrates revealed highest in vitro GTP hydrolysis-activating activity with Rab32 and Rab33B. Catalysis required Arg-803 of RUTBC1, and RUTBC1 could activate a catalytically inhibited Rab33B mutant (Q92A), in support of a dual finger mechanism for RUTBC1 action. Rab9A binding did not influence GAP activity of bead-bound RUTBC1 protein. In cells and cell extracts, RUTBC1 influenced the ability of Rab32 to bind its effector protein, Varp, consistent with a physiological role for RUTBC1 in regulating Rab32. In contrast, binding of Rab33B to its effector protein, Atg16L1, was not influenced by RUTBC1 in cells or extracts. The identification of a protein that binds Rab9A and inactivates Rab32 supports a model in which Rab9A and Rab32 act in adjacent pathways at the boundary between late endosomes and the biogenesis of lysosome-related organelles.

Endosomes
G Proteins
Membrane Recycling
Membrane Trafficking
Protein Sorting
Atg16L1
Rab GTPase
Rab Cascade
Varp

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This research was supported, in whole or in part, by National Institutes of Health Grant DK37332 (to S. R. P.).

1

Supported by National Institutes of Health Training Grant GM007276.

2

Present address: MRC Protein Phosphorylation Unit, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom.