3 research outputs found
Biomimetic Approach to Enhance Enzymatic Hydrolysis of the Synthetic Polyester Poly(1,4-butylene adipate): Fusing Binding Modules to Esterases
Mimicking a concept of nature for
the hydrolysis of biopolymers,
the <i>Thermobifida cellulosilytica</i> cutinase 1 (Thc_Cut1)
was fused to a polymer binding module (PBM) to enhance the hydrolysis
of the polyester poly(1,4-butylene adipate) (PBA). Namely, the binding
module of a polyhydroxyalkanoate depolymerase from <i>Alcaligenes
faecalis</i> (Thc_Cut1_PBM) was attached to the cutinase via
two different linker sequences varying in length. In order to investigate
the adsorption behavior, catalytically inactive mutants both of Thc_Cut1
and Thc_Cut1_PBM were successfully constructed by site-directed mutagenesis
of serine 131 to alanine. Quartz crystal microbalance with dissipation
monitoring (QCM-D) analysis revealed that the initial mass increase
during enzyme adsorption was larger for the inactive enzymes linked
with the PBM as compared to the enzyme without the PBM. The hydrolysis
rates of PBA were significantly enhanced when incubated with the active,
engineered Thc_Cut1_PBM as compared to the native Thc_Cut1. Thc_Cut1_PBM
completely hydrolyzed PBA thin films on QCM-D sensors within approximately
40 min, whereas twice as much time was required for the complete hydrolysis
by the native Thc_Cut1
Enzymatic Hydrolysis of Polyester Thin Films at the Nanoscale: Effects of Polyester Structure and Enzyme Active-Site Accessibility
Biodegradable polyesters have a large
potential to replace persistent
polymers in numerous applications and to thereby reduce the accumulation
of plastics in the environment. Ester hydrolysis by extracellular
carboxylesterases is considered the rate-limiting step in polyester
biodegradation. In this work, we systematically investigated the effects
of polyester and carboxylesterase structure on the hydrolysis of nanometer-thin
polyester films using a quartz-crystal microbalance with dissipation
monitoring. Hydrolyzability increased with increasing polyester-chain
flexibility as evidenced from differences in the hydrolysis rates
and extents of aliphatic polyesters varying in the length of their
dicarboxylic acid unit and of poly(butylene adipate-co-terephthalate)
(PBAT) polyesters varying in their terephthalate-to-adipate ratio
by Rhizopus oryzae lipase and Fusarium solani cutinase. Nanoscale nonuniformities
in the PBAT films affected enzymatic hydrolysis and were likely caused
by domains with elevated terephthalate contents that impaired enzymatic
hydrolysis. Yet, the cutinase completely hydrolyzed all PBAT films,
including films with a terephthalate-to-adipate molar ratio of one,
under environmentally relevant conditions (pH 6, 20 °C). A comparative
analysis of the hydrolysis of two model polyesters by eight different
carboxylesterases revealed increasing hydrolysis with increasing accessibility
of the enzyme active site. Therefore, this work highlights the importance
of both polyester and carboxylesterase structure to enzymatic polyester
hydrolysis
An Esterase from Anaerobic Clostridium hathewayi Can Hydrolyze Aliphatic–Aromatic Polyesters
Recently,
a variety of biodegradable polymers have been developed
as alternatives to recalcitrant materials. Although many studies on
polyester biodegradability have focused on aerobic environments, there
is much less known on biodegradation of polyesters in natural and
artificial anaerobic habitats. Consequently, the potential of anaerobic
biogas sludge to hydrolyze the synthetic compostable polyester PBAT
(poly(butylene adipate-<i>co</i>-butylene terephthalate)
was evaluated in this study. On the basis of reverse-phase high-performance
liquid chromatography (RP-HPLC) analysis, accumulation of terephthalic
acid (Ta) was observed in all anaerobic batches within the first 14
days. Thereafter, a decline of Ta was observed, which occurred presumably
due to consumption by the microbial population. The esterase Chath_Est1
from the anaerobic risk 1 strain Clostridium hathewayi DSM-13479 was found to hydrolyze PBAT. Detailed characterization
of this esterase including elucidation of the crystal structure was
performed. The crystal structure indicates that Chath_Est1 belongs
to the α/β-hydrolases family. This study gives a clear
hint that also micro-organisms in anaerobic habitats can degrade manmade
PBAT