1. Analysis of cyclotides in Viola ignobilis by Nano liquid chromatography fourier transform mass spectrometry
Hossein Hashempour, Alireza Ghassempour, Norelle L Daly, Bernhard Spengler, Andreas Römpp Protein Pept Lett. 2011 Jul;18(7):747-52. doi: 10.2174/092986611795446030.
Cyclotides are macrocyclic knotted peptides originating from plants. They are extremely stable and have a range of bioactivities including anti-HIV and insecticidal activity. Given the stability of the cyclotide framework, there is interest in using these peptides as scaffolds in drug design. In the current study, we have shown that nano-LC Fourier transform mass spectrometry (FTMS) is an effective method of analyzing cyclotides in plants. In addition, we have used this technique to find cyclotides in a novel species, Viola ignobilis (Violaceae plant family), which was collected from the West Azerbaijan province of Iran. Varv peptide A, cycloviolacin B2, and cycloviolacin O8 were found in this species. This study provides a novel method for directly analyzing cyclotide sequences without enzymatic digestion and further information regarding the distribution of cyclotides in plant species.
2. Seven novel macrocyclic polypeptides from Viola arvensis
U Göransson, T Luijendijk, S Johansson, L Bohlin, P Claeson J Nat Prod. 1999 Feb;62(2):283-6. doi: 10.1021/np9803878.
Seven novel macrocyclic polypeptides, designated as varv peptides B-H, have been isolated from the aerial parts of Viola arvensis. Their primary structures have been elucidated by automated Edman degradation and mass spectrometry. They all consist of 29 or 30 amino acid residues, covalently cyclized via the amide backbone and by three internal disulfide bridges. Their amino acid sequences are as follows: varv peptide B, cyclo-(TCFGGTCNTPGCSCDPWPMCSRNGLPVCGE); varv peptide C, cyclo-(TCVGGTCNTPGCSCSWPVCTRNGVPICGE); varv peptide D, cyclo-(TCVGGSCNTPGCSCSWPVCTRNGLPICGE); varv peptide E, cyclo-(TCVGGTCNTPGCSCSWPVCTRNGLPICGE); varv peptide F, cyclo-(TCTLGTCYTAGCSCSWPVCTRNGVPICGE); varv peptide G, cyclo-(TCFGGTCNTPGCSCDPWPVCSRNGVPVCGE); and varv peptide H, cyclo-(TCFGGTCNTPGCSCETWPVCSRNGLPVCGE). The varv peptides B-H exhibited high degrees of homology with the hitherto known macrocyclic peptides varv peptide A, kalata B1, violapeptide I, circulins A and B, and cyclopsychotride A.
3. Cyclotides Chemosensitize Glioblastoma Cells to Temozolomide
Samantha L Gerlach, Rachael A Dunlop, James S Metcalf, Sandra A Banack, Paul Alan Cox J Nat Prod. 2022 Jan 28;85(1):34-46. doi: 10.1021/acs.jnatprod.1c00595. Epub 2022 Jan 19.
Glioblastoma multiforme (GBM) is the most aggressive cancer originating in the brain, with a median survival of 12 months. Most patients do not respond to or develop resistance to the only effective chemotherapeutic drug, temozolomide (TMZ), used to treat gliomas. Novel treatment methods are critically needed. Cyclotides are plant peptides that may be promising adjuvants to TMZ chemotherapy. They exhibit antitumor activity and chemosensitize cells to doxorubicin in breast cancer studies. During this research, we optimized cyclotide isolation techniques, and several cyclotides (CyO2, CyO13, kalata B1, and varv peptide A) exhibited dose-dependent cytotoxicity in MTT assays with IC50 values of 2.15-7.92 μM against human brain astrocytoma cells (U-87 MG) and human bone marrow derived neuroblastoma cells (SH-SY5Y). CyO2 and varv peptide A increased TMZ-induced cell death in U-87 MG cultures alone and when coexposed with CyO2 or varv peptide A plus TMZ. Phase contrast microscopy of glioblastoma cells exposed to cyclotides alone and coexposed to TMZ indicated shrunken, granular cells with blebbing, and the most pronounced effects were observed with coexposure treatments of cyclotides and TMZ. Cumulative results provide the proof-of-concept that cyclotides may enhance TMZ chemotherapy, and in vivo pharmacokinetic investigations of cyclotides are warranted with respect to GBM.
