This enzyme belongs to the family of hydrolases, specifically those acting on carboxylic ester bonds. The systematic name of this enzyme class is cutin hydrolase.
Aerial plant organs are protected by a cuticle composed of an insoluble polymeric structural compound, cutin, which is a polyester composed of hydroxy and hydroxyepoxy fatty acids. Plant pathogenic fungi produce extracellular degradative enzymes that play an important role in pathogenesis. They include cutinase, which hydrolyses cutin, facilitating fungus penetration through the cuticle. Inhibition of the enzyme can prevent fungal infection through intact cuticles. Cutin monomers released from the cuticle by small amounts of cutinase on fungal spore surfaces can greatly increase the amount of cutinase secreted by the spore, the mechanism for which process is as yet unknown.
Cutinase is a serine esterase containing the classical Ser, His, Asp triad of serine hydrolases. The protein belongs to the alpha-beta class, with a central beta-sheet of 5 parallel strands covered by 5 helices on either side of the sheet. The active site cleft is partly covered by 2 thin bridges formed by amino acid side chains, by contrast with the hydrophobic lid possessed by other lipases. The protein also contains 2 disulfide bridges, which are essential for activity, their cleavage resulting in complete loss of enzymatic activity. Two cutinase-like proteins (MtCY39.35 and MtCY339.08c) have been found in the genome of the bacteria Mycobacterium tuberculosis.
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