Orexin-A and orexin-B (hypocretin-1 and hypocretin-2, respectively) are important hypothalamic neuro-peptides, which are encoded by a single mRNA transcript and stimulate food intake as well as regulate wakefulness. Here we determined the solution structure of orexin-A by NMR spectroscopy and by simulated-annealing calculation. The structural features of orexin-A involve two alpha-helices, with the hydrophobic residues disposed to on one side of helix, and hydrophilic residues to the other. A hydrophilic turn induced by two disulfide bonds provides the key difference between orexin-A and -B. With previous mutagenic studies, the derived structure of orexin-A provides us with a structure-functional view for novel drug design.
Background: A secreted peptide Pep27 initiates the cell death program in S. pneumoniae through signal transduction. This study was undertaken to evaluate the relation between the structure and cytotoxic activity of Pep27 and its analogues on cancer cells.
The structure and function of short-length amino terminal PTH analogues were studied. The substitution of Leu(7) with Phe in [Ala(3,10)Leu(7)Arg(11)]rPTH(1-11)NH(2) analogue peptides did not show any reduction in cAMP formation. Replacement of the 1st, 7th and 8th residues revealed different activities, depending upon the residue type. The substitution of Ala1 by Ser in [Ala(3,10)Leu(7)Arg(11)]rPTH(1-11)NH(2) caused nearly a complete loss of cAMP formation. Meanwhile, NMR analysis of [(Ala(1)/ Ser(1))Ala(3,10)(Leu(7)/Phe(7))Arg(11)]rPTH(1-11)NH(2) revealed an alpha-helical backbone structure with a flexible conformation at the carboxyl-terminus. The overall results suggest that 11-residue short oligopeptide analogues of PTH tend to form an alpha-helical structure and the different activities of those analogues could be associated with residue specificity rather than the secondary conformational structure.
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