Cyclotides – Circular plant peptides for protein engineering

Over the last decade, cyclotides has emerged as the largest known family of cyclic peptide and protein gene products. To date, more than 100 cyclotides have been characterized from a limited number of species from Violaceae and Rubiaceae [1,2]. These plant peptides have a unique structure that gives them an extraordinary stability. Combined with their structural diversity, cyclotides is a prime scaffold for protein engineering [3].

Our research aims to explore the potential of cyclotides for medical and biotechnological applications. For example, we have determined that a conserved Glu-residue plays a key role for their cytotoxic activity [4], and that this activity is mediated via membrane interactions [5]. The structural plasticity of the cyclotide framework is explored to set the limits of the scaffold for protein engineering. This is done by extensive studies of naturally occurring cyclotides; currently we use a combination of cDNA screening and protein isolation to access this diversity [6], and newly developed strategies for peptide synthesis [7] is used for production of mutants with improved and introduced effects. Ultimately, we aim to exploit cyclotide biosynthesis to develop an expression system of a non-native, pharmacologically active, cyclotide in planta.

The cyclotide structure, showing the continuous amide backbone and the cystine knot arrangement of the three disulfides (disulfides in ball and stick mode).

Acknowledgements: All Present and Past members of the cyclotide group in Uppsala, including Teshome Leta Aboye, Mariamawit Yonathan Yeshak, Robert Burman, Anders Herrmann, Erika Svangård, Lars Bohlin and Per Claeson.

References: 1. Göransson, U. et al. (2004) Curr Protein Pept Sci 5:317–29. 2. Plan, M. et al. (2007) Chembiochem 18:1001–11. 3. Craik, D.J. (2006) Science 311:1563–1564. 4. Herrmann, A. et al. (2006) Cell Mol Life Sci 63:235–45. 5. Svangård, E. et al. (2007)J Nat Prod 70:643–7. 6. Herrmann, A. et al. (2008) Phytochemistry 69:939–52. 7. Leta Aboye, T. et al. (2008) Chembiochem 9:103–13.