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.