PROSITE documentation PDOC00283

Bacterial ice-nucleation proteins octamer repeat

Some Gram-negative bacteria express proteins that enable them to promote the nucleation of ice at relatively high temperature (above -5 degree Celsius) [1,2,3]. These proteins are localized at the surface of the outer membrane of the bacteria and can cause frost injury to many plant species. The primary structure of these ice-nucleation proteins is highly repetitive. A central repetitive domain represents about 80% of the total sequence. This domain is mainly formed by the repetition of a conserved region of forty eight residues (48-mer). The 48-mers are themselves composed of three blocks of 16 residues (16-mer). The first eight residues of each of these 16-mers are identical. It has been proposed that the repetitive domain may be directly responsible for aligning water molecules in the seed crystal.

Schematic structure of a 48-mer region:

              [.........48.residues.repeated.domain..........]
             /              / |              | \              \
            AGYGSTxTagxxssli  AGYGSTxTagxxsxlt  AGYGSTxTaqxxsxlt
            [16.residues...]  [16.residues...]  [16.residues...]