PROSITE documentation PDOC00025

Chitin-binding type-1 domain signature and profile

Many plants respond to pathogenic attack by producing defense proteins that are capable of reversible binding to chitin, an N-acetylglucosamine polysaccharide present in the cell wall of fungi and the exoskeleton of insects. Most of these chitin-binding proteins include a common structural motif of 30 to 43 residues organized around a conserved four-disulfide core, known as the chitin-binding domain type-1 [1]. The topological arrangement of the four disulfide bonds is shown in the following figure:

                                +-------------+
                           +----|------+      |
                           |    |      |      |
                xxCgxxxxxxxCxxxxCCsxxgxCgxxxxxCxxxCxxxxC
                  |        ******|*************   |    |
                  |              |                +----+
                  +--------------+

'C': conserved cysteine involved in a disulfide bond.
'*': position of the pattern.

The structure of several chitin-binding domain type-1 have been solved, (see for example <PDB:1HEV>) [2]. The chitin-binding site is localized in a β-hairpin loop formed by the second disulfide bridge. Conserved serine and aromatic residues associated with the hairpin-loop are essential for the chitin-binding activity [3]. The chitin-binding domain type-1 displays some structural similarities with the chitin-binding domain type-2 (see <PDOC50940>).

Some of the proteins containing a chitin-binding domain type-1 are listed below:

• A number of non-leguminous plant lectins. The best characterized of these lectins are the three highly homologous wheat germ agglutinins (WGA-1, 2 and 3). WGA is an N-acetylglucosamine/N-acetylneuraminic acid binding lectin which structurally consists of a fourfold repetition of the 43 amino acid domain. The same type of structure is found in a barley root-specific lectin as well as a rice lectin.
• Plants endochitinases (EC 3.2.1.14) from class IA (see <PDOC00620>). Endochitinases are enzymes that catalyze the hydrolysis of the β-1,4 linkages of N-acetyl glucosamine polymers of chitin. Plant chitinases function as a defense against chitin containing fungal pathogens. Class IA chitinases generally contain one copy of the chitin-binding domain at their N-terminal extremity. An exception is agglutinin/chitinase [4] from the stinging nettle Urtica dioica which contains two copies of the domain.
• Hevein, a wound-induced protein found in the latex of rubber trees.
• Win1 and win2, two wound-induced proteins from potato.
• Kluyveromyces lactis killer toxin α subunit [5]. The toxin encoded by the linear plasmid pGKL1 is composed of three subunits: α, β, and γ. The γ subunit harbors toxin activity and inhibits growth of sensitive yeast strains in the G1 phase of the cell cycle; the α subunit, which is proteolytically processed from a larger precursor that also contains the β subunit, is a chitinase (see <PDOC00839>).

The profile we developed covers the whole domain.