Exploring the Reaction Mechanism of Polyethylene Terephthalate Biodegradation through QM/MM Approach.

The enzyme PETase fromIdeonella sakaiensis (IsPETase) strain 201-F6 can catalyze the hydrolysis of polyethylene terephthalate (PET), mainly converting it into mono(2-hydroxyethyl) terephthalic acid (MHET). In this study, we used quantum mechanics/molecular mechanics (QM/MM) simulations to explore the molecular details of the catalytic reaction mechanism of IsPETase in the formation of MHET. The QM region was described with AM1d/PhoT and M06-2X/6-31+G(d,p) potential. QM/MM simulations unveil the complete enzymatic PET hydrolysis mechanism and identify two possible reaction pathways for acylation and deacylation steps. The barrier obtained at M06-2X/6-31+G(d,p)/MM potential for the deacylation step corresponds to 20.4 kcal/mol, aligning with the experimental value of 18 kcal/mol. Our findings indicate that deacylation is the rate-limiting step of the process. Furthermore, per-residue interaction energy contributions revealed unfavorable contributions to the transition state of amino acids located at positions 200-230, suggesting potential sites for targeted mutations. These results can contribute to the development of more active and selective enzymes for PET depolymerization.

Microsurgical resection of an inferior cerebellar peduncle cavernous malformation: 3-Dimensional operative video.

Brainstem cavernous malformations are especially difficult to treat because of their deep location and intimate relation with eloquent structures. This is the case of a 26-year-old female presenting with dizziness, dysmetria, nystagmus and unbalance. Imaging depicted a lesion highly suggestive of a cavernous malformation in the left inferior cerebellar peduncle. Following a suboccipital midline craniotomy, the cerebellomedullary fissure was dissected and the lesion was identified bulging the surface. The malformation was completely removed with constant intraoperative neurophysiological monitoring. The patient presented improvement of initial symptoms with no new deficits. Surgical resection of brainstem cavernous malformations can be successfully performed, especially when superficial, using the inferior cerebellar peduncle as an entry zone. The video can be found here: https://youtu.be/-GGZe_CaZnQ.