Hay Dvir

Acetylcholinesterase: From 3D structure to function.

By rapid hydrolysis of the neurotransmitter, acetylcholine, acetylcholinesterase terminates neurotransmission at cholinergic synapses. Acetylcholinesterase is a very fast enzyme, functioning at a rate approaching that of a diffusion-controlled reaction. The powerful toxicity of organophosphate poisons is attributed primarily to their potent inhibition of acetylcholinesterase. Acetylcholinesterase inhibitors are utilized in the treatment of various neurological disorders, and are the principal drugs approved thus far by the FDA for management of Alzheimers disease. Many organophosphates and carbamates serve as potent insecticides, by selectively inhibiting insect acetylcholinesterase. The determination of the crystal structure of Torpedo californica acetylcholinesterase permitted visualization, for the first time, at atomic resolution, of a binding pocket for acetylcholine. It also allowed identification of the active site of acetylcholinesterase, which, unexpectedly, is located at the bottom of a deep gorge lined largely by aromatic residues. The crystal structure of recombinant human acetylcholinesterase in its apo-state is similar in its overall features to that of the Torpedo enzyme; however, the unique crystal packing reveals a novel peptide sequence which blocks access to the active-site gorge.

X‐ray structure of human acid‐β‐glucosidase, the defective enzyme in Gaucher disease

Gaucher disease, the most common lysosomal storage disease, is caused by mutations in the gene that encodes acid‐β‐glucosidase (GlcCerase). Type 1 is characterized by hepatosplenomegaly, and types 2 and 3 by early or chronic onset of severe neurological symptoms. No clear correlation exists between the ∼200 GlcCerase mutations and disease severity, although homozygosity for the common mutations N370S and L444P is associated with non‐ neuronopathic and neuronopathic disease, respectively. We report the X‐ray structure of GlcCerase at 2.0 Å resolution. The catalytic domain consists of a (β/α)8 TIM barrel, as expected for a member of the glucosidase hydrolase A clan. The distance between the catalytic residues E235 and E340 is consistent with a catalytic mechanism of retention. N370 is located on the longest α‐helix (helix 7), which has several other mutations of residues that point into the TIM barrel. Helix 7 is at the interface between the TIM barrel and a separate immunoglobulin‐like domain on which L444 is located, suggesting an important regulatory or structural role for this non‐catalytic domain. The structure provides the possibility of engineering improved GlcCerase for enzyme‐replacement therapy, and for designing structure‐based drugs aimed at restoring the activity of defective GlcCerase.

The synaptic acetylcholinesterase tetramer assembles around a polyproline II helix

Functional localization of acetylcholinesterase (AChE) in vertebrate muscle and brain depends on interaction of the tryptophan amphiphilic tetramerization (WAT) sequence, at the C‐terminus of its major splice variant (T), with a proline‐rich attachment domain (PRAD), of the anchoring proteins, collagenous (ColQ) and proline‐rich membrane anchor. The crystal structure of the WAT/PRAD complex reveals a novel supercoil structure in which four parallel WAT chains form a left‐handed superhelix around an antiparallel left‐handed PRAD helix resembling polyproline II. The WAT coiled coils possess a WWW motif making repetitive hydrophobic stacking and hydrogen‐bond interactions with the PRAD. The WAT chains are related by an ∼4‐fold screw axis around the PRAD. Each WAT makes similar but unique interactions, consistent with an asymmetric pattern of disulfide linkages between the AChE tetramer subunits and ColQ. The P59Q mutation in ColQ, which causes congenital endplate AChE deficiency, and is located within the PRAD, disrupts crucial WAT–WAT and WAT–PRAD interactions. A model is proposed for the synaptic AChET tetramer.

Acetylcholinesterase: a multifaceted target for structure-based drug design of anticholinesterase agents for the treatment of Alzheimer's disease.

The structure of Torpedo californica acetylcholinesterase is examined in complex with several inhibitors that are either in use or under development for treating Alzheimers disease. The noncovalent inhibitors vary greatly in their structures and bind to different sites of the enzyme, offering many different starting points for future drug design.

STRUCTURAL FEATURE OF AChE INHIBITOR HUPERZINE B IN NATURE AND IN THE BINDING SITE OF AChE: DENSITY FUNCTIONAL THEORY STUDY COMBINED WITH IR DETERMINATION

Quantum chemical DFT-B3LYP/6-31G method and IR spectrometry have been used to investigate the natural and binding structures of Huperzine B (HupB) in order to better understand the interaction nature between acetylcholinesterase (AChE) and its inhibitor, with the view of designing new AChE inhibitors. The predicted and experimental results reveal that both the natural state and binding form of HupB adopt the chair conformation. Furthermore, the B3LYP/6-31G results suggest that structure S1 should be the dominant form of the two possible chair structures (S1 and S2, Fig. 2). The calculated results also show that the condensed ring structure composing of rings A, B and C is very rigid. Therefore, its flexibility does not need to be considered when we try to dock this structure to its target. Indeed, this supposition is conrmed by the excellent alignment of the binding structure produced from our recent X-ray crystallographic structure of the HupB-AChE complex with the B3LYP/6-31G predicted geometry. Among all the 111 predicted vibrational bands, the mode 110, which is resulted from the stretching of the bond N2{H and having the second highest frequency, is essential for the geometrical identication. The dierence between our predicted strongest absorption band and experimental IR spectrum suggests