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- **************************************************
- * Chitin recognition or binding domain signature *
- **************************************************
-
- A conserved domain of 43 amino acids is found in several plant and fungal
- proteins that have a common binding specificity for oligosaccharides of
- N-acetylglucosamine [1]. This domain may be involved in the recognition or
- binding of chitin subunits. This domain has been found in the proteins listed
- below.
-
- - A number of non-leguminous plants 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
- acids 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. Endochitinases are
- enzymes that catalyze the hydrolysis of the beta-1,4 linkages of N-acetyl
- glucosamines 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 the agglutinin/chitinase [2] from the stinging
- nettle Urtica dioica which contains two copies of the domain.
- - Hevein [5], a wound-induced protein found in the latex of rubber trees.
- - Win1 and win2, two wound-induced proteins from potato.
- - Kluyveromyces lactis killer toxin alpha subunit [3]. The toxin encoded by
- the linear plasmid pGKL1 is composed of three subunits: alpha, beta, and
- gamma. The gamma subunit harbors the toxin activity and inhibits the growth
- of sensitive yeast strains in the G1 phase of the cell cycle; the alpha
- subunit, which is proteolytically processed from a larger precursor that
- also contains the beta subunit, is a chitinase.
-
- In chitinases, as well as in the potato wound-induced proteins, the 43-residue
- domain directly follows the signal sequence and is therefore at the N-terminal
- of the mature protein; in the killer toxin alpha subunit it is located in the
- central section of the protein.
-
- The domain contains eight conserved cysteine residues, which have been shown,
- in WGA, to be all involved in disulfide bonds. 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.
-
- -Consensus pattern: C-x(4,5)-C-C-S-x(2)-G-x-C-G-x(4)-[FYW]-C
- [The five C's are involved in disulfide bonds]
- -Sequences known to belong to this class detected by the pattern: ALL.
- -Other sequence(s) detected in SWISS-PROT: NONE.
- -Last update: October 1993 / Pattern and text revised.
-
- [ 1] Wright H.T., Sandrasegaram G., Wright C.S.
- J. Mol. Evol. 33:283-294(1991).
- [ 2] Lerner D.R., Raikhel N.V.
- J. Biol. Chem. 267:11085-11091(1992).
- [ 3] Butler A.R., O'Donnel R.W., Martin V.J., Gooday G.W., Stark M.J.R.
- Eur. J. Biochem. 199:483-488(1991).
-