Why do scientists try to predict the structure of a membrane protein by this indirect means when the technique of X-ray crystallography would reveal the structure directly

RAS is a very important protein that belongs to a class of protein referred to as GTPases and plays a crucial role in switching on pathways that control cell growth, proliferation, apoptosis and differentiation and migration. For RAS to become inactive it must hydrolyze GTP to GDP which slows down the process of cell proliferation. Mutation in one copies of RAS will result to cancer because the mutated copy will permanently attach to GTP and remain in activated form which will lead to uncontrollable cell division and hence development of cancer.