Frank Heinrich: Structure of the KRas / Raf1 protein complex at the lipid membrane
Place: Kemicentrum, Lecture hall B
Contact: tommy [dot] nylander [at] fkem1 [dot] lu [dot] se
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A Physical Chemistry seminar by Frank Heinrich, Associate Research Professor and NIST Associate, Physics Department, Carnegie Mellon University, Pittsburgh, PA, USA.
Ras genes are the most frequently mutated oncogenes in human cancer. The KRas isoform has proven to be an elusive drug target, in part because the membrane-bound state of protein in complex with effector proteins is unknown. We present structural studies of farnesylated KRas-FMe GppNHp by itself and in complex with partial constructs of Raf1 at the membrane using neutron reflectometry (NR). In contrast to structural models predominantly based on molecular simulation that predict a close membrane engagement of KRas, we present direct experimental data in which the G-domain of KRas is found to be located on average about 30 Å away from the membrane while the hypervariable region serves as a flexible membrane tether. Binding to Raf1-RBD (Ras Binding Domain) and Raf1-RBD-CRD (Cysteine Rich Domain) does not affect this conformation. Complimentary NMR-PRE data is in agreement with the NR result and provides the orientation of KRas by itself and in complex with Raf1 at the membrane on a residue level. This work challenges the current view of KRas dynamics at the lipid membrane and provides mechanistic insight into KRas signaling and inhibition. Methodical improvements in NR by our group that allow for the presented detail in characterization of protein complexes at lipid membranes are discussed.
Frank Heinrich1,2, Que Van3, Mathias Lösche1,2, Andrew Stephen3
1Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA
2NIST Center for Neutron Research, Gaithersburg, MD, USA
3Frederick National Laboratory for Cancer Research, Frederick, MD, USA