Solution NMR studies of integral polytopic α-helical membrane proteins: the structure determination of the seven-helix transmembrane receptor sensory rhodopsin II, pSRII.

About 30% of the proteins encoded in the genome are expressed as membrane proteins but these represent <1% of all the structures solved today. In view of the physiological and pharmaceutical significance of membrane proteins it is clear that a better and more comprehensive understanding of their three-dimensional (3D) structures at atomic resolution is required. α-Helical integral membrane proteins are generally more difficult to work with than β-barrel-type proteins and this has particularly been true for the polytopic members such as the large family of seven-helical proteins. In this chapter we describe the practical aspects of the solution-state NMR spectroscopy structure determination of the seven-helical transmembrane (7-TM) protein receptor sensory rhodopsin pSRII from the haloalkaliphilic archaeon Natronomonas pharaonis reconstituted in detergent micelles. This is the first time that a three-dimensional structure of a 7-TM protein has been determined by NMR.