Kissper, a kiwi fruit peptide with channel‐like activity: Structural and functional features

Abstract

Kissper is a 39-residue peptide isolated from kiwi fruit (Actinidia deliciosa). Its primary structure, elucidated by direct protein sequencing, is identical to the N-terminal region of kiwellin, a recently reported kiwi fruit allergenic protein, suggesting that kissper derives from the in vivo processing of kiwellin. The peptide does not show high sequence identity with any other polypeptide of known function. However, it displays a pattern of cysteines similar, but not identical, to those observed in some plant and animal proteins, including toxins involved in defence mechanisms. A number of these proteins are also active on mammalian cells. Functional characterization of kissper showed pH-dependent and voltage-gated pore-forming activity, together with anion selectivity and channeling in model synthetic PLMs, made up of POPC and of DOPS:DOPE:POPC. A 2DNMR analysis indicates that in aqueous solution kissper has only short regions of regular secondary structure, without any evident similarity with other bioactive peptides. Comparative analysis of the structural and functional features suggests that kissper is a member of a new class of pore-forming peptides with potential effects on human health.

Studies on the Effect of Salts on the Channel Activity of Kissper, a Kiwi Fruit Peptide

“…The channel activity of Kissper might depend on hydrophobic and hydrophilic interactions of the Kissper molecules with membrane lipids, as suggested for some bioactive peptides. This result is confirmed by our previous study in which we showed that kissper interacts with lipid bilayers forming channel-like pores with anion selectivity in KCl [18].…”

“…PLMs made up of DOPS:DOPE:POPC (27:27:18, w:w:w) in 1% n-decane (Fluka) were formed as previously described [18,22]. The channel current was monitored in different salt solutions, i.e.…”

“…Its isolation and purification processes and its structural characterization were reported in our previous study [18].…”

“…The primary structure of kissper shows the highest identity (69%) with N-terminal regions of both the putative kiwellin of potato leaves and the cDNA-derived sequence of Gripp 22 from grape, and lower identity (31-47%) with regions of several peptides and proteins having a variety of functions, such as toxins, protease inhibitors and proteins containing the EGF-like cysteine-rich motif [18]. Kissper has six cysteine residues forming three disulfide bridges (Cys4-Cys36, Cys8-Cys20, Cys14-Cys25).…”

“…In fact, the analysis of NOESY data indicates that the peptide conformation is consistent with the presence of a β-hairpin with the two short β-strands encompassing Ile19-Ile21 and Lys24-Asn26, connected through a central loop centered on Lys22-Gly23. Moreover, the residues Gly32-Ile35 are involved in a short helix [18].…”