| 1. |
- Burman, Robert, et al.
(författare)
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Chemistry and Biology of Cyclotides : Circular Plant Peptides Outside the Box
- 2014
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Ingår i: Journal of natural products (Print). - : American Chemical Society (ACS). - 0163-3864 .- 1520-6025. ; 77:3, s. 724-736
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Forskningsöversikt (refereegranskat)abstract
- Cyclotides stand out as the largest family of circular proteins of plant origin hitherto known, with more than 280 sequences isolated at peptide level and many more predicted from gene sequences. Their unusual stability resulting from the signature cyclic cystine knot (CCK) motif has triggered a broad interest in these molecules for potential therapeutic and agricultural applications. Since the time of the first cyclotide discovery, our laboratory in Uppsala has been engaged in cyclotide discovery as well as the development of protocols to isolate and characterize these seamless peptides. We have also developed methods to chemically synthesize cyclotides by Fmoc-SPPS, which are useful in protein grafting applications. In this review, experience in cyclotide research over two decades and the recent literature related to their structures, synthesis, and folding as well the recent proof-of-concept findings on their use as "epitope" stabilizing scaffolds are summarized.
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| 2. |
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| 3. |
- Gunasekera, Sunithi, et al.
(författare)
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Fmoc-SPPS based synthesis of bioactive cyclic peptides via N-acylurea intermediates
- 2012
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Ingår i: Journal of Peptide Science. - : Wiley. - 1075-2617 .- 1099-1387. ; 18:suppl 1, s. S182-S182
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The plant cyclotides form the largest family of cyclic peptides(1). They contain a signature motif referred to as the cyclic cystine knot, which is derived from the cyclic backbone and three inter-knotted disulfide bonds. Intriguingly, cyclotides can be boiled, treated with chemicals or enzymes without disrupting their overall fold. Thus, they are sometimes labeled as ultra-stable proteins. In addition, cyclotides are tolerant to mutations, and as a scaffold they can successfully accommodate foreign bioactive epitopes of variable sequences(2). Cyclotides share many of these properties with another disulfide containing cyclic plant peptide, the sunflower trypsin inhibitor 1 (SFTI-1)(3). Emerging evidence indicates that cyclotides and SFTI-1 are valuable not only as peptide stabilizing scaffolds; in combination with their cell penetrating properties, these disulfide rich cyclic peptides have significance as intracellular drug carriers. Although both peptides are genetically encoded, studies to ascertain the exact mechanisms of their biosynthesis are currently on going. Thus, the synthesis of cyclotides and SFTI-1 are currently restricted to chemical means. We have recently adapted a Fmoc-SPPS method for cyclic peptide synthesis, via N-acylurea intermediates with the assistance of microwave irradiation.This method is a safe and convenient alternative to Boc-SPPS and has the ability to be automated conveniently. Using this method, parent scaffolds as well as several cyclotide and SFTI-1 analogues with potential antimicrobial and matrix metalloprotease activities were synthesized. With the rising interest in the cyclization concept as a tool to impart stability on unstable peptides, the cyclic peptide synthesis method adapted herein is anticipated to have numerous applications.1. Burman, R.; Gunasekera, S.; Stromstedt, A.; Rosengren, J.; Goransson, U. J. Biol. Chem. 2012 (in press)2. Gunasekera, S.; Foley, F. M.; Clark, R. J.; Sando, L.; Fabri, L. J.; Craik, D. J.; Daly, N. L. J. Med. Chem. 2008, 51, 7697.3. Chan, L. Y.; Gunasekera, S.; Henriques, S. T.; Worth, N. F.; Le, S. J.; Clark, R. J.; Campbell, J. H.; Craik, D. J.; Daly, N. L. Blood 2011, 118, 6709.
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| 4. |
- Gunasekera, Sunithi, et al.
(författare)
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Making Ends Meet : Microwave-Accelerated Synthesis of Cyclic and Disulfide Rich Proteins Via In Situ Thioesterification and Native Chemical Ligation
- 2013
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Ingår i: International Journal of Peptide Research and Therapeutics. - : Springer Science and Business Media LLC. - 1573-3149 .- 1573-3904. ; 19:1- SI, s. 43-54
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Tidskriftsartikel (refereegranskat)abstract
- The development of synthetic methodologies for cyclic peptides is driven by the discovery of cyclic peptide drug scaffolds such as the plant-derived cyclotides, sunflower trypsin inhibitor 1 (SFTI-1) and the development of cyclized conotoxins. Currently, the native chemical ligation reaction between an N-terminal cysteine and C-terminal thioester group remains the most robust method to obtain a head-to-tail cyclized peptide. Peptidyl thioesters are effectively generated by Boc SPPS. However, their generation is challenging using Fmoc SPPS because thioester linkers are not stable to repeated piperidine exposure during deprotection. Herein we describe a Fmoc-based protocol for synthesizing cyclic peptides adapted for microwave assisted solid phase peptide synthesis. The protocol relies on the linker Di-Fmoc-3,4-diaminobenzoic acid, and we demonstrate the use of Gly, Ser, Arg and Ile as C-terminal amino acids (using HBTU and HATU as coupling reagents). Following synthesis, an N-acylurea moiety is generated at the C-terminal of the peptide; the resin bound acylurea peptide is then deprotected and cleaved from the resin. The fully deprotected peptide undergoes thiolysis in aqueous buffer, generating the thioester in situ. Ultimately, the head-to-tail cyclized peptide is obtained via native chemical ligation. Two naturally occurring cyclic peptides, the prototypical Mobius cyclotide kalata B1 and SFTI-1 were synthesized efficiently, avoiding potential branching at the diamino linker, using the optimized protocol. In addition, we demonstrate the possibility to use the approach for the synthesis of long and synthetically challenging linear sequences, by the ligation of two truncated fragments of a 50-residue long plant defensin.
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| 5. |
- Gunasekera, Sunithi, et al.
(författare)
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Strategies for macrocyclic cyclotide synthesis
- 2010
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Ingår i: Posters 001-067: Synthetic Chemistry of Amino Acids and Peptides. - : Wiley. ; , s. 65-65
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Göransson, Ulf, et al.
(författare)
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Circular Proteins from Plants and Fungi
- 2012
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 287:32, s. 27001-27006
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Forskningsöversikt (refereegranskat)abstract
- Circular proteins, defined as head-to-tail cyclized polypeptides originating from ribosomal synthesis, represent a novel class of natural products attracting increasing interest. From a scientific point of view, these compounds raise questions of where and why they occur in nature and how they are formed. From a rational point of view, these proteins and their structural concept may be exploited for crop protection and novel pharmaceuticals. Here, we review the current knowledge of three protein families: cyclotides and circular sunflower trypsin inhibitors from the kingdom of plants and the Amanita toxins from fungi. A particular emphasis is placed on their biological origin, structure, and activity. In addition, the opportunity for discovery of novel circular proteins and recent insights into their mechanism of action are discussed.
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| 7. |
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| 8. |
- Koehbach, Johannes, et al.
(författare)
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Oxytocic plant cyclotides as templates for peptide G protein-coupled receptor ligand design
- 2013
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 110:52, s. 21183-21188
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Tidskriftsartikel (refereegranskat)abstract
- Cyclotides are plant peptides comprising a circular backbone and three conserved disulfide bonds that confer them with exceptional stability. They were originally discovered in Oldenlandia affinis based on their use in traditional African medicine to accelerate labor. Recently, cyclotides have been identified in numerous plant species of the coffee, violet, cucurbit, pea, potato, and grass families. Their unique structural topology, high stability, and tolerance to sequence variation make them promising templates for the development of peptide-based pharmaceuticals. However, the mechanisms underlying their biological activities remain largely unknown; specifically, a receptor for a native cyclotide has not been reported hitherto. Using bioactivity-guided fractionation of an herbal peptide extract known to indigenous healers as "kalata-kalata," the cyclotide kalata B7 was found to induce strong contractility on human uterine smooth muscle cells. Radioligand displacement and second messenger-based reporter assays confirmed the oxytocin and vasopressin V-1a receptors, members of the G protein-coupled receptor family, as molecular targets for this cyclotide. Furthermore, we show that cyclotides can serve as templates for the design of selective G protein-coupled receptor ligands by generating an oxytocin-like peptide with nanomolar affinity. This nonapeptide elicited dose-dependent contractions on human myometrium. These observations provide a proof of concept for the development of cyclotide-based peptide ligands.
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| 9. |
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| 10. |
- Park, Sungkyu, et al.
(författare)
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An Efficient Approach for the Total Synthesis of Cyclotides by Microwave Assisted Fmoc-SPPS
- 2010
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Ingår i: International Journal of Peptide Research and Therapeutics. - : Springer Science and Business Media LLC. - 1573-3149 .- 1573-3904. ; 16:3, s. 167-176
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Tidskriftsartikel (refereegranskat)abstract
- Cyclotides are mini-proteins of approximately 30 amino acid residues that have a unique structure consisting of a head-to-tail cyclized backbone and a knotted arrangement of three disulfide bonds. This unique cyclotide structure provides exceptional stability to chemical, enzymatic and thermal treatments and has been implicated as an ideal drug scaffold for the development into agricultural and biotechnological agents. In the current work, we present the first method for microwave assisted Fmoc-SPPS of cyclotides. This protocol adopts a strategy that combines optimized microwave assisted chemical reactions for Fmoc-SPPS of the peptide backbone, the cleavage of the protected peptide and the introduction of a thioester at the C-terminal carboxylic acid to obtain the head-to-tail cyclized cyclotide backbone by native chemical ligation. To exemplify the utility of this protocol in the synthesis of a wide array of different cyclotide sequences we synthesized representative members from the three cyclotide subfamilies-the Mobius kalata B1, the bracelet cycloviolacin O2 and the trypsin inhibitory MCoTI-II. In addition, a "one pot" reaction promoting both cyclization and oxidative folding of crude peptide thioester was adapted for kalata B1 and MCoTI-II.
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| 11. |
- Park, SungKyu, et al.
(författare)
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Microwave-assisted total synthesis of macrocyclic cystine knot miniproteins
- 2010
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Ingår i: Journal of Peptide Science. - : Wiley. - 1075-2617 .- 1099-1387. ; 16:S1, s. 79-79
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Microwave-assisted total synthesis of macrocyclic cystine knot miniproteins SK Park, S Gunasekera, T Aboye, U Göransson Division of pharmacognosy, Uppsala university, UPPSALA, Sweden Cyclotides are mini-proteins of approximately 30 amino acids residues that have a unique structure consisting of a head-to-tail cyclic backbone with a knotted arrangement of three disulfide bonds [1]. This unique structure provides exceptional stability to chemical, enzymatic and thermal treatments [2,3]. Cyclotides display various bioactivities, such as anti-HIV, uterotonic, cytotoxic, and insecticidal activity [4]. Due to the unique structural stability, cyclotides have been implicated as ideal drug scaffolds and for development into agricultural and biotechnological agents [2]. In the current work, we represent the first method for total synthesis of cyclotides based on Fmoc-SPPS assisted by microwave. This protocol adopts a strategy that combines the optimized microwave assisted chemical reactions for Fmoc-SPPS of peptide backbone synthesis, thioesterification of the C-terminal carboxylic acid of the peptide and a one pot reaction that promotes cyclisation through native chemical ligation and oxidative folding. The application of this protocol was exemplified for the synthesis of two prototypic cyclotides; kalata B1 and MCOTI-II
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