Acta Crystallographica Section D

Biological Crystallography

Volume 63, Part 7 (July 2007)

research papers

Acta Cryst. (2007). D63, 769-779 [ doi:10.1107/S0907444907019725 ]

Structure of the small GTPase Rab27b shows an unexpected swapped dimer

L. M. G. Chavas, S. Torii, H. Kamikubo, M. Kawasaki, K. Ihara, R. Kato, M. Kataoka, T. Izumi and S. Wakatsuki

Abstract: Members of the Rab family of small GTPases regulate membrane traffic within the cell by recruiting their specific effectors in a nucleotide-dependent manner. The Rab27 subfamily consists of Rab27a and Rab27b, which share 70% sequence identity. By interacting with a large set of effector proteins such as melanophilin and granuphilin, both Rab27a and Rab27b regulate the exocytosis of secretory lysosomes. Here, the crystal structures of mouse Rab27b in complex with GDP have been determined in three distinct crystal lattices. Surprisingly, Rab27b-GDP exists in an open conformation with protruding switch and interswitch regions, which are stabilized through dimerization by means of domain-swapping in the crystals. In contrast, small-angle X-ray scattering measurements showed an extended monomer form of Rab27b in solution. The observed dimer formation of Rab27b-GDP in the crystals would restrain the highly flexible switch regions. Possible biological implications of this atypical structure of Rab27b and its plausible influence in effector interaction are discussed.

PDB references: 2iey, 2iez and 2if0

Keywords: Rabs; GTPase; domain-swapping; dimer.


	Portable Document Format (PDF) file (129.1 kbytes) [ doi:10.1107/S0907444907019725/be5081sup1.pdf ] Supplementary Figure 1. Initial phase determination.

	Portable Document Format (PDF) file (132.1 kbytes) [ doi:10.1107/S0907444907019725/be5081sup2.pdf ] Supplementayr Figure 2. Structural comparison with Rabs.

	Portable Document Format (PDF) file (83.8 kbytes) [ doi:10.1107/S0907444907019725/be5081sup3.pdf ] Supplementary Figure 4. Size-exclusion chromatography spectrum pf Rab27b-GDP.

	Portable Document Format (PDF) file (47.8 kbytes) [ doi:10.1107/S0907444907019725/be5081sup4.pdf ] Supplementary Figure 4. Pull-down experiments.

	Portable Document Format (PDF) file (138.6 kbytes) [ doi:10.1107/S0907444907019725/be5081sup5.pdf ] Supplementary Figure 5. Co-immunoprecipitation analysis of Rab27b in transfected cells.

	Portable Document Format (PDF) file (26.4 kbytes) [ doi:10.1107/S0907444907019725/be5081sup6.pdf ] Supplementary Figure 6. DLS experiments.

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