Thermophilic polyester hydrolases (PES-H) have recently
enabled
biocatalytic recycling of the mass-produced synthetic polyester polyethylene
terephthalate (PET), which has found widespread use in the packaging
and textile industries. The growing demand for efficient PET hydrolases
prompted us to solve high-resolution crystal structures of two metagenome-derived
enzymes (PES-H1 and PES-H2) and notably also in complex with various
PET substrate analogues. Structural analyses and computational modeling
using molecular dynamics simulations provided an understanding of
how product inhibition and multiple substrate binding modes influence
key mechanistic steps of enzymatic PET hydrolysis. Key residues involved
in substrate-binding and those identified previously as mutational
hotspots in homologous enzymes were subjected to mutagenesis. At 72
°C, the L92F/Q94Y variant of PES-H1 exhibited 2.3-fold and 3.4-fold
improved hydrolytic activity against amorphous PET films and pretreated
real-world PET waste, respectively. The R204C/S250C variant of PES-H1
had a 6.4 °C higher melting temperature than the wild-type enzyme
but retained similar hydrolytic activity. Under optimal reaction conditions,
the L92F/Q94Y variant of PES-H1 hydrolyzed low-crystallinity PET materials
2.2-fold more efficiently than LCC ICCG, which was previously the
most active PET hydrolase reported in the literature. This property
makes the L92F/Q94Y variant of PES-H1 a good candidate for future
applications in industrial plastic recycling processes.
The first two cage
based crystalline covalent organic frameworks, cage-COF-1 and cage-COF-2, were constructed from a prism-like
three-aldehyde-containing molecular cage. The cage contains two horizontal
phloroglucinol and three vertical triazine moieties forming three
identical V-shaped cavities. By reacting with p-phenylenediamine
and 4,4′-biphenyldiamine, the two cage-COFs were formed with
a hexagonal skeleton and possess a unique structure. Due to the pillared
cage nodes, the linkers are hanging with their π-surfaces but
not C–H sites exposed to the pore, and enjoy certain rotational
dynamics as suggested by 13C CP/MAS NMR. The antidirection
of the diimine linkages leads to rippled layers which pack in unique
ABC mode through alternate stacking of the cage twosided faces in
both AB and AC layers. Such packing forms trigonal channels along c axis which are interconnected in ab plane
due to the large open space created across the hanging linkers, resembling
the porous characteristics of 3D COFs. The cage-COFs have a permanent
porosity and can adsorb CO2 facilitated by the intrinsic
cage cavities that serve as prime adsorption sites. The unprecedented
cage-COFs not only merge the borderline of 2D and 3D COFs but also
bridge porous organic cages to extended crystalline organic frameworks.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.