Division of Pharmaceutical Chemistry and Technology, Faculty of Pharmacy, POB 56, FI-00014 University of Helsinki, Finland.
School of Pharmacy, University of Eastern Finland, POB 1627, FI-70211 Kuopio, Finland.
Peptides. 2018 Apr;102:54-60. doi: 10.1016/j.peptides.2018.02.004. Epub 2018 Feb 21.
The peptides orexin-A and -B, the endogenous agonists of the orexin receptors, have similar 19-amino-acid C-termini which retain full maximum response as truncated peptides with only marginally reduced potency, while further N-terminal truncations successively reduce the activity. The peptides have been suggested to bind in an α-helical conformation, and truncation beyond a certain critical length is likely to disrupt the overall helical structure. In this study, we set out to stabilize the α-helical conformation of orexin-A via peptide stapling at four different sites. At a suggested hinge region, we varied the length of the cross-linker as well as replaced the staple with two α-aminoisobutyric acid residues. Modifications close to the peptide C-terminus, which is crucial for activity, were not allowed. However, central and N-terminal modifications yielded bioactive peptides, albeit with decreased potencies. This provides evidence that the orexin receptors can accommodate and be activated by α-helical peptides. The decrease in potency is likely linked to a stabilization of suboptimal peptide conformation or blocking of peptide backbone-receptor interactions at the hinge region by the helical stabilization or the modified amino acids.
肽类食欲素-A 和 -B 是食欲素受体的内源性激动剂，它们具有相似的 19 个氨基酸 C 末端，作为截短肽保留了完整的最大反应，只是效力略有降低，而进一步的 N 端截断则依次降低活性。这些肽类被认为以α-螺旋构象结合，并且超过一定关键长度的截断可能会破坏整体螺旋结构。在这项研究中，我们着手通过在四个不同位点对食欲素-A 进行肽键固定来稳定α-螺旋构象。在一个建议的铰链区域，我们改变了交联剂的长度，并将订书钉替换为两个α-氨基异丁酸残基。不允许对肽 C 末端进行修饰，因为这对活性至关重要。然而，对中心和 N 端进行修饰产生了具有生物活性的肽，尽管效力降低。这提供了证据表明，食欲素受体可以容纳并被α-螺旋肽激活。效力降低可能与次优肽构象的稳定或铰链区域的螺旋稳定或修饰氨基酸对肽骨架-受体相互作用的阻断有关。
