About 20% of colorectal cancers have mutations in the B-Raf gene which is a serine/threonine kinase which mediates cellular response to groth signals. Raf is activated when a phosphate is added to Thr 598 and Ser 601. The mutation in B-Raf found in cancer cells makes it constitutively active and does not need activation via Ras protein which is a requirement for a normal Raf activation. 95% of mutatnt B-Raf gene have glutamate in place of Val 599. Why do you suppose that B-Raf with glutamate at position 599 is active?