The self-association of the cyclotide kalata B2 in solution is guided by hydrophobic interactions

Rosengren, K. Johan, Daly, Norelle L., Harvey, Peta J., and Craik, David J. (2013) The self-association of the cyclotide kalata B2 in solution is guided by hydrophobic interactions. Peptide Science, 100 (5). pp. 453-460.

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The cyclotides are a family of small head-to-tail cyclic plant defense proteins. In addition to their cyclic backbone, cyclotides comprise three disulfide bonds in a knotted arrangement, resulting in a highly cross-braced structure that provides exceptional chemical and proteolytic stability. A number of bioactivities have been associated with cyclotides, including insecticidal, antimicrobial, anti-viral and cytotoxic, and these activities are related to an ability to target and disrupt biological membranes. Kalata B2 and to a lesser extent kalata B1, isolated from Oldenlandia affinis, self-associate to tetramers and octamers in aqueous buffers, and this oligomerization has been suggested to be relevant for their ability to form pores in membranes. Here we demonstrate by solution NMR spectroscopy analysis that the oligomerization of kalata B2 is concentration dependent and that it involves the packing of hydrophobic residues normally exposed on the surface of kalata B2 into a multimeric hydrophobic core. Interestingly, the hydrophobic surface that is "quenched" has previously been shown to be responsible for the ability of kalata B2 to insert into membranes. Thus, it seems unlikely that the oligomers observed in aqueous solution are related to any multimeric state present in a membrane environment, and responsible for the formation of pores. The ability to self-associate might alternatively provide a mechanism for preventing self-toxicity when stored at high concentrations in intracellular compartments.

Item ID: 32119
Item Type: Article (Research - C1)
ISSN: 1097-0282
Keywords: cyclic peptides; cyclotides; kalata; NMR; self-association; structure
Funders: National Medical and Health Research Council (NHMRC), Australian Research Council (ARC)
Date Deposited: 30 Apr 2014 01:15
FoR Codes: 03 CHEMICAL SCIENCES > 0304 Medicinal and Biomolecular Chemistry > 030401 Biologically Active Molecules @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970103 Expanding Knowledge in the Chemical Sciences @ 100%
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