A repeating 11‐mer amino acid motif and plant desiccation

Abstract

Among the proteins that accumulate as plant seeds desiccate are several protein families that are composed principally of a tandemly repeated 11‐mer amino acid motif. Proteins containing the same motif accumulate in the desiccating leaves of a desiccation‐tolerant plant species. This motif is characterized by apolar residues in positions 1, 2, 5 and 9, and charged or amide residues in positions 3, 6, 7, 8 and 11. An α helical arrangement of the 11‐mer repeating unit gives an amphiphilic helix whose hydrophobic stripe twists in a right‐handed fashion around the helix. Should these proteins dimerize via binding of their hydrophobic faces, a right‐handed coiled coil would be formed. Such a structure has not previously been observed. A conceivable function for these proteins in ion sequestration in the desiccated state is proposed.