Isolation of a Novel Cutinase Homolog with Polyethylene Terephthalate-Degrading Activity from Leaf-Branch Compost by Using a Metagenomic Approach

The gene encoding a cutinase homolog, LC-cutinase, was cloned from a fosmid library of a leaf-branch compost metagenome by functional screening using tributyrin agar plates. LC-cutinase shows the highest amino acid sequence identity of 59.7% to Thermomonospora curvata lipase. It also shows the 57.4% identity to Thermobifida fusca cutinase. When LC-cutinase without a putative signal peptide was secreted to the periplasm of Escherichia coli cells with the assistance of the pelB leader sequence, more than 50% of the recombinant protein, termed LC-cutinase(star), was excreted into the extracellular medium. It was purified and characterized. LC-cutinase(star) hydrolyzed various fatty acid monoesters with acyl chain lengths of 2 to 18, with a preference for short-chain substrates (C-4 substrate at most) most optimally at pH 8.5 and 50 degrees C, but could not hydrolyze olive oil. It lost activity with half-lives of 40 min at 70 degrees C and 7 min at 80 degrees C. LC-cutinase(star) had an ability to degrade poly(epsilon-caprolactone) and polyethylene terephthalate (PET). The specific PET-degrading activity of LC-cutinase(star) was determined to be 12 mg/h/mg of enzyme (2.7 mg/h/mu kat of pNP-butyrate-degrading activity) at pH 8.0 and 50 degrees C. This activity is higher than those of the bacterial and fungal cutinases reported thus far, suggesting that LC-cutinase(star) not only serves as a good model for understanding the molecular mechanism of PET-degrading enzyme but also is potentially applicable for surface modification and degradation of PET.