Helix packing and orientation in the transmembrane dimer of gp55-P of the spleen focus forming virus

gp55- P is a dimeric membrane protein with a single transmembrane helix that is coded by the env gene of the polycythemic strain of the spleen focus forming virus. gp55- P activates the erythropoietin ( Epo) receptor through specific transmembrane helix interactions, leading to Epo- independent growth of erythroid progenitors and eventually promoting erythroleukemia. We describe the use of magic angle spinning deuterium NMR to establish the structure of the transmembrane dimer of gp55- P in model membranes. Comparison of the deuterium lineshapes of leucines in the center ( Leu(396 - 399)) and at the ends ( Leu(385), Leu(407)) of the transmembrane sequence shows that gp55- P has a right- handed crossing angle with Leu(399) packed in the dimer interface. We discuss the implications of the structure of the gp55- P transmembrane dimer for activation of the Epo receptor.