Dynamic binding of HRas·GTP to the allosteric site of Sos investigated by solution NMR

Ras proteins, which are important for cellular signaling and cancer development, are activated by guanine nucleotide exchange factors, among which Son-of-Sevenless (Sos) plays a pivotal role. The catalytic activity of Sos is regulated by its interaction with Ras·GTP at the allosteric site of Sos. Although much research has been conducted, the structural details of the dynamic interactions between Ras·GTP and Sos at the allosteric site in solution are not completely understood. In this study, paramagnetic relaxation enhancement (PRE) was used to examine the binding of HRas·GTP to the allosteric site of Sos^cat. A site-specific paramagnetic probe was attached to Sos^cat, revealing crucial interface information, which was then used to construct structural models of the HRas-Sos^cat complex via HADDOCK. Our results indicate that the dominant conformation of HRas·GTP bound to Sos^cat at the allosteric site is highly consistent with the established crystal structure while also identifying a transient conformation with a novel interface between HRas and Sos unseen in previous crystal structures.