InterPro: IPR014733 Barwin-like endoglucanase

Beta barrels are commonly observed in protein structures. They are classified in terms of two integral parameters: the number of strands in the sheet, n, and the shear number, S, a measure of the stagger of the strands in the beta-sheet. These two parameters have been shown to determine the major geometrical features of beta-barrels. Six-stranded beta-barrels with a pseudo-twofold axis are found in several proteins. One involving parallel strands forming two psi structures is known as the double-psi barrel. The first psi structure consists of the loop connecting strands beta1 and beta2 (a 'psi loop') and the strand beta5, whereas the second psi structure consists of the loop connecting strands beta4 and beta5 and the strand beta2. All the psi structures in double-psi barrels have a unique handedness, in that beta1 (beta4), beta2 (beta5) and the loop following beta5 (beta2) form a right-handed helix. The unique handedness may be related to the fact that the twisting angle between the parallel pair of strands is always larger than that between the antiparallel pair [1].

This domain is found in Barwin proteins and some glycoside hydrolases. Barwin is a basic protein isolated from aqueous extracts of barley seeds. It is 125 amino acids in length, and contains six cysteine residues that combine to form three disulphide bridges [2, 3]. Comparative analysis shows the sequence to be highly similar to a 122 amino acid stretch in the C-terminal of the products of two wound-induced genes (win1 and win2) from potato, the product of the hevein gene of rubber trees, and pathogenesis-related protein 4 from tobacco. The high levels of similarity to these proteins, and their ability to bind saccharides, suggest that the barwin domain may be involved in a common defence mechanism in plants.