The structure of the guanine nucleotide exchange factor rlf in complex with the small g-Protein ral identifies conformational intermediates of the exchange reaction and the basis for the selectivity.
CDC25 homology domain (CDC25-HD) containing Guanine Nucleotide Exchange Factors
(GEFs) initiate signalling by small G-proteins of the Ras-family. Each GEF acts
on a small subset of the G-proteins only, thus providing signalling selectivity.
Rlf is a GEF with selectivity for the G-proteins RalA and RalB. Here the crystal
structure of Rlf in complex with Ral is determined. The Rlf·Ral complex
crystallised into two different crystal forms, which represent different steps
of the exchange reaction. Thereby general insight in the CDC25-HD catalysed
nucleotide exchange is obtained. In addition, the basis for the selectivity of
the interaction is investigated. The exchange activity is monitored by the use
of recombinant proteins. Selectivity determinants in the binding interface are
identified and confirmed by a mutational study.
