Data‐driven model of the KRas4B/Calmodulin complex

• Published in: The FASEB journal 2021-05, Vol.35 (S1), p.n/a, Article fasebj.2021.35.S1.04058
• Main Authors: Ojeda, Monica, Marcus, Kendra, Jang, Hyunbum, Banerjee, Avik, Makowski, Lee, Nussinov, Ruth, Gaponenko, Vadim, Mattos, Carla
• Format: Article
• Language: English
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.2021.35.S1.04058

KRas4B (henceforth called KRas) is a small GTPase that regulates activation of a variety of signaling pathways, including the Raf/MEK/ERK pathway, leading to cell proliferation, survival, and differentiation. Activation of these signaling pathways is dependent on the nucleotide‐bound state of KRas: GTP‐bound KRas “turns on” signaling while GDP‐bound KRas “turns off” signaling. Interestingly, KRas is the only one of the three Ras isoforms that interacts with Ca2+‐bound calmodulin (CaM). However, attempts to crystallize the KRas/CaM complex have proven difficult due to the flexible nature of the hypervariable region (HVR) of KRas as well as the linker region of CaM. We present a model of the complex containing unprocessed full‐length KRas in complex with CaM, guided by small angle x‐ray scattering (SAXS), NMR nuclear overhouser effects and chemical shift perturbations. The low‐resolution envelope of the complex shows that CaM interacts with KRas in an open conformation. The NOEs suggest that the HVR adopts a helical conformation in the region that interacts with CaM. Our low‐resolution experimental data, together with published chemical shift perturbations lead to a model of the KRas/CaM complex that fits our SAXS envelop well (ꭓ=1.97). This model will be refined using molecular dynamics simulations.