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Updated: Aug 23, 2026

Comparing the Affinity of GTPase-binding Proteins using Competition Assays
Published on: October 8, 2015
Loop domain peptides from the SOS ras-guanine nucleotide exchange protein, identified from molecular dynamics
Lyndon Chie1, Fred K Friedman, Thomas Duncan
1Department of Pathology and Laboratory Medicine, New York Harbor VA Medical Center, Brooklyn, NY 11209, USA.
Abstract:
In the accompanying paper, we found, using molecular dynamics calculations, four domains of the ras-specific SOS guanine nucleotide exchange protein (residues 589-601, 654-675, 746-761, and 980-989) that differ markedly in conformation when SOS is complexed with either oncogenic (Val 12-) ras-p21 or wild-type ras-p21. Three of these domains contain three crystallographically undefined loops that we modeled in these calculations, and one is a newly identified non-loop domain containing SOS residues 980-989. We have now synthesized peptides corresponding to these four domains and find that all of them block Val 12-ras-p21-induced oocyte maturation. All of them also block insulin-induced oocyte maturation, but two of these peptides, corresponding to SOS residues 589-601 and 980-989, block oncogenic ras to a significantly greater extent. These results suggest that SOS contains domains, including the three loop domains, that are important for ras signaling and that several of these domains can activate different pathways specific to oncogenic or wild-type ras-p21.
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