Crystallization and preliminary X-ray crystallographic studies of Rab6A'(Q72L): a GTP-locked form

Abstract

Rab6A, a member of the Ras superfamily of small G proteins, is involved in the regulation of vesicle trafficking, which is critical for endocytosis, cell differentiation and cell growth. Rab6A can exist in two isoforms termed Rab6A and Rab6A'. The substitution of Gln72 by Leu (Q72L) in the Rab6A family blocks GTP-hydrolysis activity, and this mutation usually causes the Rab6A protein to be in a constitutively active form. In this study, in order to understand the functional uniqueness of Rab6A' and the molecular mechanism of the control of activity by GTP and GDP from the crystal structure, a Rab6A'(Q72L) mutant form was overexpressed in Escherichia coli with an engineered N-terminal His tag. Rab6A'(Q72L) was then purified to homogeneity and crystallized at 293 K. X-ray diffraction data were collected to a resolution of 1.9 Å from a crystal belonging to space group P22(1)2(1) with unit-cell parameters a = 36.84, b = 96.78, c = 109.99 Å. The asymmetric unit was estimated to contain two molecules.

Figure 1

Gel-filtration chromatography and SDS–PAGE of Rab6A′(Q72L)

Figure 2

Crystal of Rab6A′(Q72L). Crystals were grown in 3 d in the presence of 20% PEG 8000, 0.3 M calcium acetate, 0.1 M sodium cacodylate pH 6.7. The approximate dimensions of the crystals were 0.2 × 0.2 × 0.1 mm.

Figure 3

A diffraction image (1° oscillation) from a Rab6A′(Q72L) crystal with a 1.9 Å resolution limit.