PROSITE documentation PDOC50940

Chitin-binding type-2 domain profile

The species distribution of the chitin-binding type-2 domain is complementary to the chitin-binding type-1 domain (see <PDOC00025>). The type-2 is mainly found in animal and baculovirus proteins while the type-1 is found in plant and fungi. Type-2 is characterized by having a 6-cysteine motif: C-x(13,20)-C-x(5,6)-C-x(9,19)-C-x(10,14)-C-x(4,14)-C and several aromatic residues [1].

The structure of the chitin-binding domain of tachycitin has been solved (see <PDB:1DQC>) [2]. It revealed that tachycitin shares a remarkable structural similarity with the chitin-binding type-1 domain of hevein. The overall structure forms a distorted β-sandwich constructed by three-stranded and two-stranded β-sheets connected through a bending loop (Cys-40-Leu-44). The precise chitin binding site (Cys-40 to Gly-60) is perfectly superposable with the chitin binding site of hevein. Furthermore a disulfide bridge connecting Cys-40 and Cys-53 is also present at the same location in the hevein structure [2].

Some protein known to contain a chitin-binding type-2 domain are listed below:

• Animal class-II chitinase. It degrades chitin and chitotriose. In mammals it may participate in the defense against nematodes and other pathogens [3].
• Tachycitin, an antimicrobial protein of horseshoe crab hemocytes.
• Peritrophin-A, a component of peritrophic matrices (acellular linings in the gut of most insects that comprise proteins and sugar polymers, including chitin).
• Drosophila Tequila protein, a serine protease involved in immune response.
• Drosophila Hemolectin, a sugar binding protein involved in defense response.

The profile we developed covers the whole domain.