Radiation Damage and Racemic Protein Crystallography Reveal the Unique Structure of the GASA/Snakin Protein Superfamily

Angew Chem Int Ed Engl. 2016 Jul 4;55(28):7930-3. doi: 10.1002/anie.201602719. Epub 2016 May 4.


Proteins from the GASA/snakin superfamily are common in plant proteomes and have diverse functions, including hormonal crosstalk, development, and defense. One 63-residue member of this family, snakin-1, an antimicrobial protein from potatoes, has previously been chemically synthesized in a fully active form. Herein the 1.5 Å structure of snakin-1, determined by a novel combination of racemic protein crystallization and radiation-damage-induced phasing (RIP), is reported. Racemic crystals of snakin-1 and quasi-racemic crystals incorporating an unnatural 4-iodophenylalanine residue were prepared from chemically synthesized d- and l-proteins. Breakage of the C-I bonds in the quasi-racemic crystals facilitated structure determination by RIP. The crystal structure reveals a unique protein fold with six disulfide crosslinks, presenting a distinct electrostatic surface that may target the protein to microbial cell surfaces.

Keywords: peptides; protein structures; racemic protein crystallography; solid-phase synthesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Anti-Infective Agents / chemistry*
  • Crystallization
  • Crystallography, X-Ray / methods
  • Models, Molecular
  • Plant Proteins / chemistry*
  • Protein Conformation
  • Solanum tuberosum / chemistry*


  • Anti-Infective Agents
  • Plant Proteins
  • SN1 protein, Solanum tuberosum