PLP-dependent enzymes described on this review are attractive targets for enzyme engineering towards their application in an industrial biotechnology framework.

Alzheimer's disease is associated with the deposition of extracellular senile plaques, made primarily of amyloid-β (Aβ), particularly peptides Aβ 1−42 and Aβ 1−40 . Neprilysin, or neutral endopeptidase (NEP), catalyzes proteolysis of the amyloid peptides (Aβ) and is recognized as one of the major regulators of the levels of these peptides in the brain, preventing Aβ accumulation and plaque formation. Here, we used a combination of techniques to elucidate the mechanism of Aβ binding and cleavage by NEP. Our findings indicate that the Aβ 31−X cleavage products remain bound to the neprilysin active site, reducing proteolytic activity. Interestingly, it was already shown that this Aβ 31−35 sequence is also critical for recognition of Aβ peptides by other targets, such as the serpin-enzyme complex receptor in neuronal cells.

The catalytic mechanism of threonine aldolase (TA) was herein studied in atomic detail employing the computational ONIOM hybrid QM/MM methodology. TA is a PLP-dependent enzyme that catalyzes the retro-aldol cleavage of threonine into glycine and acetaldehyde, as well as the reverse reaction. This enzyme is currently seen as the optimal approach for the regioselective synthesis of β-hydroxy-α-amino acids (HAAs), which are very difficult to obtain by standard methods. The results obtained herein show that the catalytic mechanism of TA occurs in three steps: (i) deprotonation of the hydroxyl group of EA1, (ii) covalent bond cleavage, and (iii) hydrolysis. According to the Gibbs free energy profile, the rate-limiting step of the catalytic process is the covalent bond cleavage, which results in the formation of acetaldehyde. The calculated energy barrier for this step is 16.7 kcal mol–1, which agrees very well with the kinetic data available in the literature (17.4 kcal mol–1). All these results can now be used for the optimization of the synthesis of HAAs that serve as building blocks of several commercial drugs, such as antibiotics, immunosuppressants, and the anti-Parkinson’s disease drug l-threo-3,4-dihydroxyphenylserine.

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BIA 10-2474 is a time-dependent inhibitor of fatty acid amide hydrolase (FAAH) that was under clinical development for the treatment of neurological conditions when the program was terminated after one subject died and four were hospitalized with neurological symptoms during a first-in-human clinical study. The present work describes the mechanism of FAAH inhibition by BIA 10-2474 as a target-specific covalent inhibition, supported by quantum mechanics and molecular modelling studies. The inhibitor incorporates a weakly reactive electrophile which, upon specific binding to the enzyme's active site, is positioned to react readily with the catalytic residues. The reactivity is enhanced on-site by the increased molarity at the reaction site and by specific inductive interactions with FAAH. In the second stage, the inhibitor reacts with the enzyme's catalytic nucleophile to form a covalent enzymeinhibitor adduct. The hydrolysis of this adduct is shown to be unlikely under physiological conditions, therefore leading to irreversible inactivation of FAAH. The results also reveal the important role played by FAAH Thr236 in the reaction with BIA 10-2474, which is specific to FAAH and is not present in other serine hydrolases. It forms a hydrogen bond with the imidazole nitrogen of the inhibitor and helps lowering the activation free energy of the first step of the reaction, by pre-orienting and stabilizing the inhibitor in a near-reactive configuration. In the second step, Thr236 can also serve as a mechanistic alternative to protonate the leaving group.[a] N.

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The synthesis of a 1,5-lactone 2,4- O-alkylidene-d-erythrose derivative was found to be a highly stereoselective template in Michael addition trough the reaction of a d-erythrosyl 1,5-lactone derivative with nitrogen and sulfur nucleophiles. The sulfur adducts formed are 1 (d-erythrose derivative):1 (nucleophile), and the nitrogen adducts are 1:2. Both were then treated under HCl to give 2,6-dideoxy-4-functionalized-d- ribono-hexono-1,4-lactone by a reaction cascade in high overall yield. Reaction's scale up even improves the yield. The theoretical and computational results clearly explain the origin of the stereoselectivity, and the energetic course of reactions starting with nitrogen and sulfide nucleophiles. Considering that the 1,4-lactones obtained in this work offer a new molecular scaffold for organic synthesis, these new results provide a solid theoretical platform that can be used to speed up synthesis of other derivatives in a stereo- and regioselective way.