Cryo-EM Structure of a Dimeric B-Raf:14-3-3 Complex Reveals Asymmetry in the Active Sites of B-Raf Kinases
This week we profile a recent publication in Science from the laboratory of Dr. Sriram Subramaniam (pictured) at UBC.
Can you provide a brief overview of your lab’s current research focus?
Our research program is focused on exploring the frontiers of structural biology and drug design using cryo-electron microscopy (cryo-EM), as they relate to imaging molecules, viruses and cells with the central goal of accelerating the development of effective agents for treating cancer, brain disorders and infectious diseases such as HIV and influenza.
What is the significance of the findings in this publication?
The main finding of this paper is the mechanism of action of a key enzyme that is mutated in 50% of melanomas. This class of enzymes, known as Raf kinases, are among the key conduits for the transmission of outside signals to the inside of cells. B-Raf enzymes, when active, work as pairs (dimers). These pairs sit on a “platform of proteins” known as 14-3-3 in order to function properly. Our study was able to show, using cryo-EM, that the active site of one of the two B-Raf molecules in the pair is closer to the 14-3-3 platform than its partner. The one that is closer to the platform inserts its tail into the active site of its neighbor, resulting in an arrangement where the proximal B-Raf remains active, but the activity of its neighbor is blocked.
Our finding sheds light on a paradoxical feature of Raf inhibition. Many inhibitors, such as those used to target melanomas and other cancers, when present in low amounts end up achieving exactly the opposite result, enhancing Raf activity instead of blocking it. What our findings shows is that these seemingly opposite properties of inhibition and activation are intimately linked, even when no inhibitor is present by the special arrangement of the B-Raf tail segment.
What are the next steps for this research?
This unusual property of Raf by a wide range of inhibitors is puzzling, and has restricted the full potential of small-molecule therapy targeting B-Raf. Our discovery will enable the design of more effective drugs against cancer targets such as B-Raf. This is aligned with the core mission of the Canada Excellence Research Chairs program to leverage our deep expertise in cryo-EM to enable structure-guided drug discovery and lower the rates of late stage failure in clinical trials.
This work was funded by: