Structure and Activity of the Leaf-Specific Cyclotide vhl-2

Abstract

Cyclotides are plant-derived macrocyclic peptides with potential applications in the pharmaceutical and agricultural industries. In addition to their presumed natural function as host-defence peptides arising from their insecticidal activity, their other biological activities include antimicrobial, haemolytic, and cytotoxic activities, but at present, only limited information is available on the structural and chemical features that are important for these various activities. In the current study, we determined the three-dimensional structure of vhl-2, a leaf-specific cyclotide. Although the characteristic cyclic cystine knot fold of other cyclotides is maintained in vhl-2, it has more potent haemolytic activity than well-characterized cyclotides such as kalata B1 and kalata B8. Analysis of surface hydrophobicity and haemolytic activity for a range of cyclotides indicates a correlation between them, with increasing hydrophobicity resulting in increased haemolytic activity. This correlation is consistent with membrane binding being a vital step in mediating the various cytotoxic activities of cyclotides. The gene sequence for vhl-2 was determined and indicates that vhl-2 is processed from a multidomain precursor protein that also encodes the cyclotide cycloviolacin H3.

Biomedicine in the environment: Cyclotides constitute potent natural toxins in plants and soil bacteria

“…This observation is not supported by the results in the present study, where kB1 and kB2 that have different hydrophobicities show similar EC50 values. Contrary to the findings of Daly et al [36], the most hydrophilic cyclotide of the three cyclotides studied in the present study (cyO2) is the most potent of the three. However, the bracelet family, of which cyO2 is a member, was not included in the study of Daly et al [36].…”

“…Contrary to the findings of Daly et al [36], the most hydrophilic cyclotide of the three cyclotides studied in the present study (cyO2) is the most potent of the three. However, the bracelet family, of which cyO2 is a member, was not included in the study of Daly et al [36]. In line with our results, Pränting et al [20] found cyO2 to be the most potent cyclotide of all the cyclotides tested, which included kB1 and kB2.…”

“…A correlation between bioactivity and hydrophobicity has been observed for kB1, kB2, and two other Möbius cyclotides, with increasing hydrophobicity of the cyclotide surface resulting in increasing bioactivity [36]. This observation is not supported by the results in the present study, where kB1 and kB2 that have different hydrophobicities show similar EC50 values.…”

Discovery of Cyclotides from Australasian Plants

“…Cycloviolacin O32 GAPVCGETCFGGTCNTPGCTCDPWPVCTND M [112] Cycloviolacin O33 GLPVCGETCVGGTCNTPYCTCSWPVCTRD M [112] Cycloviolacin O34 GLPVCGETCVGGTCNTEYCTCSWPVCTRD M [112] Cycloviolacin O35 GLPVCGETCVGGTCNTPYCFCSWPVCTRD M [112] Cycloviolacin O36 GLPTCGETCFGGTCNTPGCTCDPFPVCTHD M [112] Viola hederacea Widely grown Cycloviolacin H1 GIPCGESCVYIPCLTSAIGCSCKSKVCYRN B [61,96] garden plant Cycloviolacin H2 AIACGESCVYIPCFIPGCSCRNRVCYLN B [113] Cycloviolacin H3 GLPVCGETCFGGTCNTPGCICDPWPVCTRN M [113] Cycloviolacin H4 GIPCAESCVWIPCTVTALLGCSCSNNVCYN B [114] Vhl-1 SISCGESCAMISFCFTEVIGCSCKNKVCYLN B [113] Vhl-2 GLPVCGETCFTGTCYTNGCTCDPWPVCTRN M [113,115] Vhr1 GIPCAESCVWIPCTVTALLGCSCSNKVCYN B [96] Viola pubescens Mt Tomah botanic gardens Vpub A GVIPCGESCVFIPCISAVIGCSCKSKVCYRN B [116] Vpub B GIIPCGESCVFIPCITSVVGCSCKSKVCYKN B [116] Vpub C GIIPCGESCVFIPCITSIVGCSCKSKVCYKN B [116] Viola arvensis Victorian Highlands Varv peptide A GLPVCGETCVGGTCNTPGCSCSWPVCTRN M [95,117] Melicytus angustifolius RBG, Melbourne Mang A GFPTCGETCTLGTCNTPGCTCSWPICTRD M [116] Melicytus chathamicus NSW and Norfolk Is Mech 1 GVIPCGESCVFIPCINKKKCSCKNKVCYRD B [118] Mech 2 GLPTCGETCTLGKCNTPKCTCNWPICYKD M [118] Mech 3 GLPTCGETCTLGKCNTPKCTCNWPICYKN M [118] Mech 4 GSIPCGESCVYIPCISSLLGCSCKSKVCYKD B [118] Mech 5 GVIPCGESCVFIPCISSVVGCTCKNKVCYRD B [118] Mech 6 GVIPCGESCVFIPCISSVVGCTCKNKVCYRN B [118] Mech 7 GIPICGETCTIGTCNTPGCTCSWPVCTRD M [118] Melicytus dentatus NSW and Victoria Mden A GIPTCGETCTLGTCNTPGCTCSWPICTKN M [116] Mden B GLPICGETCFTGKCYTPGCTCSYPICKKN M [116] Mden C GKPICGETCFKGKCYTPGCTCSYPVCKKN M [116] Mden E GIPCGESCVYIPCITAAIGCSCKSKVCYRN B [116] Mden F GLPICGETCFFGKCNTPKCTCINPICYKN M [116] Mden G GIPCAESCVYIPCITAALGCSCKNK...…”

Highlights of the 2009 New South Wales Southern Highlands Conference on Heterocyclic Chemistry

“…For example, structural analogues of the thaxtomin natural products have been synthesized and evaluated for phytotoxicity (Smith et al [8] ), and a new family of constrained azabicyclic homocholine analogues have been synthesized and evaluated for nicotinic acetylcholine receptor antagonist activity (McLeod et al [9] ). In contrast, a study of the subtleties of the threedimensional structure of vhl-2, a leaf-specific cyclotide, and its surface hydrophobicity has provided evidence for membrane binding and a relationship to haemolytic activity (Craik et al [10] ). The synthetic challenge associated with complex and novel structures is often sufficient to drive research programs and these efforts then make available larger quantities of material for biological studies.…”