Solution structure of a new hypothalamic neuropeptide, human hypocretin-2/orexin-B

Orexin-A and orexin-B (also called hypocretin-1 and hypocretin-2, respectiv ely) are novel hypothalamic neuropeptides encoded by a single mRNA transcri pt; they stimulate food intake. We have determined the three-dimensional so lution structure of human hypocretin-2/orexin-B using two-dimensional H-1-N MR data and dynamical simulated annealing calculations. On the basis of NOE s, (3)J(HN alpha) coupling constants and hydrogen-deuterium exchange rates together with chemical shift indices, human hypocretin-2/orexin-B was deduc ed to consist of two ol-helices connected with a short linker in both H2O a nd 30% trifluoroethanol solutions. The helical axis of helix I is oriented about 60-80 degrees relative to helix II. Hybrid distance geometry and simu lated-annealing protocols were used to generate an ensemble of 30 structure s with no constraint violations greater than 0.03 nm for distances and 3 de grees for angles. In addition, human hypocretin-2/orexin-B shares a similar secondary-structural motif with human neuropeptide Y. This result can form the basis for further study on ligand-receptor recognition of human orexin receptors.