Cutinases

Cutinases are a class of extracellular esterases that hydrolyze cutin, the insoluble polyester component of the plant cuticle. They are produced by fungi and some bacteria and play a role in nutrient acquisition from plant litter and in penetrating plant surfaces.

Most cutinases are small secreted proteins with an alpha/beta hydrolase fold. They employ a catalytic triad of serine, histidine, and aspartate and carry a conserved motif around the active serine, typically GxSxG. The enzymes operate via a serine-initiated acyl-enzyme mechanism and often require few cofactors for activity.

Substrates include cutin as their natural target, but many cutinases also hydrolyze simple esters and some synthetic polyesters under appropriate conditions. Their substrate scope and optimal conditions (pH, temperature) vary by enzyme and source; many are most active at neutral to mildly alkaline pH and moderate temperatures, with activity modulated by structural features such as disulfide bonds and surface loops.

Occurrence and production: fungal cutinases include Fusarium solani pisi cutinase (FsC) and Humicola insolens cutinase; bacterial cutinases have been described in Thermobifida species and other actinomycetes. These enzymes are typically secreted into the extracellular medium, often with short signal peptides for secretion.

Applications and research: cutinases are studied for environmental and biotechnological uses, including degradation of plant-derived polymers, biocatalysis for ester synthesis, and potential plastic-degrading processes when combined with other plastic-hydrolyzing enzymes. Ongoing work aims to improve stability, broaden substrate range, and tailor activity for industrial processes.

Regulation: expression is often induced by contact with cutin-related substrates and by plant-related signals, enabling microbes to exploit plant surfaces and litter.