Poster Presentation 5th Modern Solid Phase Peptide Synthesis Symposium 2015

Investigation into the racemic X-ray structure of the antimicrobial peptide snakin-1 (#62)

Ho Yeung 1 , Yuliana Yosaatmadja 1 , Christopher J Squire 1 , Paul W. R Harris 1 2 , Edward N Baker 1 , Margaret A Brimble 1 2 3
  1. School of Biological Sciences, University of Auckland, Auckland, New Zealand
  2. School of Chemical Sciences, University of Auckland, Auckland, New Zealand
  3. Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, Auckland, New Zealand

Snakin-1 is a 63 residue antimicrobial protein originally isolated from potato (Solanum tuberosum) which is active against a number of bacterial and fungal phytopathogens such as Clavibacter michiganensis, Pseudomonas syringae and Fusarium solani.1  It is a member of the GASA (gibberellic acid stimulated in Arabidopsis)/snakin family and the mature protein consists of a GASA domain incorporating six intramolecular disulfide bonds. These proteins are found in a variety of plant species and appear to be involved in a range of functions including cell elongation and cell division.2  It has also been speculated that the 12 conserved cysteines in these proteins perform a role in redox regulation.2  The structure of these GASA/snakin proteins is not known and their amino acid sequences do not correspond to any known structural motifs.

We have recently completed the total chemical synthesis of native snakin-1 and showed that its antimicrobial activity is comparable to that of the naturally occurring protein.3  To understand how this small protein functions we have determined its three-dimensional structure by X-ray crystallography using a quasi-racemic protein system.4 Phase information for structural determination was obtained by radiation-damage induced phasing.5 

 The structure of snakin-1 appears to be novel, different to known classes of cysteine-rich plant antimicrobial peptides. Its features include a large and distinctly electropositive loop that we speculate to be membrane targeting, and a two helix bundle which is a potential membrane-interacting feature able to disrupt the structural integrity of its target bacteria.

  1. Segura, A.; Moreno, M.; Madueño, F.; Molina, A.; García-Olmedo, F., Snakin-1, a Peptide from Potato That Is Active against Plant Pathogens. Mol Plant-Microbe Interact. 1999, 12, 16-23.
  2. Nahirñak, V.; Almasia, N. I.; Hopp, H. E.; Vazquez-Rovere, C., Snakin/Gasa Proteins. Plant signal behav. 2012, 7, 1004-1008.
  3. Harris, P. W.; Yang, S. H.; Molina, A.; López, G.; Middleditch, M.; Brimble, M. A., Plant Antimicrobial Peptides Snakin-1 and Snakin-2: Chemical Synthesis and Insights into the Disulfide Connectivity. Chem. Eur. J. 2014, 20, 5102-5110.
  4. Yeates, T. O.; Kent, S. B. H., Racemic Protein Crystallography. Annu Rev Biophys. 2012, 41, 41-61.
  5. Ravelli, R. B. G.; Leiros, H.-K. S.; Pan, B.; Caffrey, M.; McSweeney, S., Specific Radiation Damage Can Be Used to Solve Macromolecular Crystal Structures. Structure 2003, 11, 217-224.