PDBsum entry 1xd4

Signaling protein

PDB id: 1xd4

Contents

Protein chain

824 a.a.

References listed in PDB file

Key reference

Title

Structural analysis of autoinhibition in the ras activator son of sevenless.

Authors

H.Sondermann, S.M.Soisson, S.Boykevisch, S.S.Yang, D.Bar-Sagi, J.Kuriyan.

Ref.

Cell, 2004, 119, 393-405. [DOI no: 10.1016/j.cell.2004.10.005]

PubMed id

15507210

Abstract

The classical model for the activation of the nucleotide exchange factor Son of sevenless (SOS) involves its recruitment to the membrane, where it engages Ras. The recent discovery that Ras*GTP is an allosteric activator of SOS indicated that the regulation of SOS is more complex than originally envisaged. We now present crystallographic and biochemical analyses of a construct of SOS that contains the Dbl homology-pleckstrin homology (DH-PH) and catalytic domains and show that the DH-PH unit blocks the allosteric binding site for Ras and suppresses the activity of SOS. SOS is dependent on Ras binding to the allosteric site for both a lower level of activity, which is a result of Ras*GDP binding, and maximal activity, which requires Ras*GTP. The action of the DH-PH unit gates a reciprocal interaction between Ras and SOS, in which Ras converts SOS from low to high activity forms as Ras*GDP is converted to Ras*GTP by SOS.

Figure 1.
Figure 1. Structure of SOS^DH-PH-cat(A) Domain organization of SOS and overview of a ternary Ras:SOS complex. The crystal structure of the Ras:SOS^cat:Ras^Y64A•GppNp ternary complex is shown (Margarit et al., 2003; PDB code 1NVV). The helical hairpin of the Cdc25 domain is shown in orange.(B) The crystal structure of SOS^DH-PH-cat. Two orthogonal views are shown with coloring according to the diagram shown in (A).(C) Comparison of SOS^DH-PH-cat with the structure of the ternary Ras:SOS^cat:Ras•GTP complex (PDB code 1NVV). The structures were aligned through superpositioning of the two respective Rem domains of SOS^DH-PH-cat and SOS^cat. Ras at the catalytic site is not shown for clarity (see [A]). Note that the distal Ras^Y64A•GppNp (green) in the ternary complex overlaps with the DH domain of SOS^DH-PH-cat. A close-up view of the Rem-Cdc25 interface is shown (right).

Figure 6.
Figure 6. Activation of ERK MAP Kinase by SOSCOS1 cells were transiently cotransfected with HA-tagged ERK2 and T7-tagged SOS constructs as indicated. ERK2 activation was measured in serum-starved cells by an immunoprecipitated kinase-kinase assay using myelin basic protein (MBP) as a substrate. Results were normalized to the vector control reaction. Western blots detecting T7- and HA-tagged proteins are shown. (A) Activation of ERK2 by SOS^cat and SOS^cat mutants. Results shown in the bar diagram are from three independent experiments. Error bars indicate standard deviations of three independent experiments. The amout of ^32P incorporation into MBP was quantified by phosphorimaging. Autoradiograms and Western blots shown are from a single representative experiment. (B) Activation of ERK2 by SOS truncations. Results shown are from a single representative experiment. Experiments were repeated three times with similar results.

The above figures are reprinted by permission from Cell Press: Cell (2004, 119, 393-405) copyright 2004.