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Structure
Structure of Rab27B
General informations: To obtain structural information on the complex of mouse Rab27B and Slac-a, a C-terminally truncated form of the GTPase-deficient mutant Rab27B (Q78L) was used. In fact, full size of Rab27B is 218 amino acids long whereas the truncated form of Rab27B contains only the GTPase domain (residues 1 to 201). [1] [2]
Pq est ce qu’on utilize un mutant? Pour simplifier la cristallo ?
Detailed structure: The structure of Rab27B in the complex contains a central six stranded beta sheet (ß1-6) flanked by five alpha helices (α1–5). Like other Ras-like small GTPases, Rab27B binds with GTP and Mg2+ in the conserved nucleotide-binding site (also see figure 2). Rab27B adopt a globular form in the complex. The ß2 and ß3 loop(residues 55-64) and α3-ß5 loop (residues122-126) of Rab27B are both regions involved in Slac2-a binding. [3]
The complex Rab27B/Slac2-a can only be formed when Rab27B is in a GTP form. This can be explain because of the changing of shape between Rab27B in the GTP and GDP form. (See figure 3) Rab27B–GTP adopts a compact monomer conformation, while an extended conformation was observed for GDP-bound Rab27B. Switch 1 and switch 2 of Rab27B play an important role in this changing of conformation. In fact, switch 1 and 2 allow GTP binding by making hydrogen bond with its γ-phosphate, and this way also allow Slac2-a binding.(see next paragraph) But in the complex Rab27B/GDP switch 1 and switch 2 exist completely apart from the bound GDP, so that there are no inter-actions with Slac2-a and no binding.
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