Tacrine-melatonin hybrids were designed and synthesized as new multifunctional drug candidates for Alzheimer's disease. These compounds may simultaneously palliate intellectual deficits and protect the brain against both beta-amyloid (A beta) peptide and oxidative stress. They show improved cholinergic and antioxidant properties, and are more potent and selective inhibitors of human acetylcholinesterase (hAChE) than tacrine. They also capture free radicals better than melatonin. Molecular modeling studies show that these hybrids target both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. At sub-micromolar concentrations they efficiently displace the binding of propidium iodide from the PAS and could thus inhibit A beta peptide aggregation promoted by AChE. Moreover, they also inhibit A beta self-aggregation and display neuroprotective properties in a human neuroblastoma line against cell death induced by various toxic insults, such as A beta(25-35), H(2)O(2), and rotenone. Finally, they exhibit low toxicity and may be able to penetrate the central nervous system according to an in vitro parallel artificial membrane permeability assay for the blood-brain barrier (PAMPA-BBB).

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Pneumococcal bacteriophage-encoded lysins are modular proteins that have been shown to act as enzymatic antimicrobial agents (enzybiotics) in treatment of streptococcal infections. The first x-ray crystal structures of the Cpl-1 lysin, encoded by the pneumococcal phage Cp-1, in complex with three bacterial cell wall peptidoglycan (PG) analogues are reported herein. The Cpl-1 structure is folded in two well defined modules, one responsible for anchoring to the pneumococcal cell wall and the other, a catalytic module, that hydrolyzes the PG. Conformational rearrangement of Tyr-127 is a critical event in molecular recognition of a stretch of five saccharide rings of the polymeric peptidoglycan (cell wall). The PG is bound at a stretch of the surface that is defined as the peptidoglycan-binding sites 1 and 2, the juncture of which catalysis takes place. The peptidoglycan-binding site 1 binds to a stretch of three saccharides of the peptidoglycan in a conformation essentially identical to that of the peptidoglycan in solution. In contrast, binding of two peptidoglycan saccharides at the peptidoglycan-binding site 2 introduces a kink into the solution structure of the peptidoglycan, en route to catalytic turnover. These findings provide the first structural evidence on recognition of the peptidoglycan and shed light on the discrete events of cell wall degradation by Cpl-1.Streptococcus pneumoniae is one of the most common and important human pathogens, which causes serious life-threatening diseases such as acute otitis media, pneumonia, sepsis, and meningitis. Pneumococcal infections are associated with high morbidity and mortality, especially among children, the elderly, and the immune-depressed patients. The widespread emergence of antibiotic resistance and the lack of highly effective pneumococcal vaccines against all serotypes of this organism give urgency to elucidation of the molecular processes involved in its pathogenicity (1, 2).The peptidoglycan (PG) 3 scaffold of the bacterial cell wall is a repeating GlcNAc-N-acetylmuramic (MurNAc) disaccharide (GlcNAc-(␤-1,4)-MurNAc) unit having a pentapeptide attached to the D-lactyl moiety of each MurNAc unit. All known pneumococcal bacteriophages encode an amidase or a lysozyme, which hydrolyzes the PG at the final stage of the phage reproductive cycle, leading to bacterial cell lysis. These enzymes, known collectively as endolysins, have been shown to be highly efficient in killing pneumococci in vitro and can eradicate this organism from the upper respiratory tract or from the bloodstream of mice (3, 4) acting as new antimicrobial agents (i.e. enzybiotics). In addition, Cpl-1 lysin and Pal amidase encoded by phage Dp-1 act in a synergistic manner in a sepsis mouse model (5); this synergy has also been confirmed in in vitro experiments with Cpl-1 and penicillin or gentamicin (6). Very recently, the creation of a new animal model of otitis media has been reported (7). Using this new mouse model, it has been demonstrated that Cpl-1 could eliminate colonization with S. p...

p-Coumaric acid decarboxylases (PDCs) catalyze the nonoxidative decarboxylation of hydroxycinnamic acids to generate the corresponding vinyl derivatives. Despite the biotechnological relevance of PDCs in food industry, their catalytic mechanism remains largely unknown. Here, we report insights into the structural basis of catalysis for the homodimeric PDC from Lactobacillus plantarum (LpPDC). The global fold of LpPDC is based on a flattened beta-barrel surrounding an internal cavity. Crystallographic and functional analyses of single-point mutants of residues located within this cavity have permitted identifying a potential substrate-binding pocket and also to provide structural evidences for rearrangements of surface loops so that they can modulate the accessibility to the active site. Finally, combination of the structural and functional data with in silico results enables us to propose a two-step catalytic mechanism for decarboxylation of p-coumaric acid by PDCs where Glu71 is involved in proton transfer, and Tyr18 and Tyr20 are involved in the proper substrate orientation and in the release of the CO(2) product.