- Crystal structure of the dimeric extracellular domain of human carbonic anhydrase XII, a bitopic membrane protein overexpressed in certain cancer tumor cells. Whittington, D.A., Waheed, A., Ulmasov, B., Shah, G.N., Grubb, J.H., Sly, W.S., Christianson, D.W. Proc. Natl. Acad. Sci. U.S.A. (2001)