Sandbox 250: Difference between revisions

Mentors: Joel Sussman, Weissman Institule of Science, and Lars Westblade, Touro College of Pharmacy.

<applet load='1fss' size='300' frame='true' align='left' scene='Sandbox_250/Ache_fas2/15' caption='AChE in complex with FAS_II'/>

Acetylcholinesterase(AChE) is essential for the hydrolysis of the neurotransmitter acetylcholine(ACh), and therefore the termination of the nerve impulse in cholinergic synapses. Irreversible inhibition of AChE can lead to increased levels of ACh in cholinergic synapses and ultimately death. Conversely, suppressed levels of ACh may lead to memory deficits associated with Alzheimer's disease. AChE has a deep(20Å) and narrow(5Å) gorge lined with 14 aromatic residues, with its active site at the bottom of the gorge. Initially, ACh binds to the peripheral anionic site(PAS)  of AChE and is funneled down the gorge to the active site by interactions between the aromatic rings of the 14 aromatic residues and the quaternary ammonium ion of ACh. At the active site, ACh is oriented for hydrolysis by interactions between the catalytic anionic ion site and the quaternary ammonium ion of ACh. The Fasciculin-II (FAS-II)toxin, a component of the East African Green Mamba snake(''Dendroaspis angusticeps'') venom, inhibits AChE by binding to the top of the active-site gorge, including residues that form the PAS; thus preventing ACh from entering the active-site gorge. The Hostos-Lincoln Academy Students Modeling A Research Topic(S.M.A.R.T) team and the Center for BioMolecular Modeling have designed and fabricated two physical models using a combination of computational molecular modeling and three-dimensional(3D) printing technology: ''Torpedo californica''(''Tc'') AChE in complex with a modeled ACh ligand and ''Tc''AChE in complex with FAS-II.

==='''Designing Physical Models to Tell the Story of Acetylcholinesterase'''===

Reflected in our design are two key concepts of AChE biology: the mechanism by which AChE hydrolyses ACh (the substrate traffic story), and how the Green Mamba Snake toxin, FAS-II, inhibits the hydrolysis of ACh (the inhibition story). Two physical models were designed and fabricated using a combination of computational molecular modeling and 3D printing technology: ''Tc'' AChE in complex with a modeled ACh ligand, and ''Tc'' AChE in complex with FAS-II. Both models were designed using the respective protein data bank (PDB) files: 2ace for the ''Tc''AChE/ACh complex and 1fss for the''Tc''AChE'FAS-II complex, and Rasmol computer modeling program.  

<applet load='2ace' size='300' frame='true' align='left' scene='Sandbox_250/Ache_ach/1' caption='AChE/ACh'/>

===='''Features of the Substrate Traffic Story:''a Model of'' AChE/ACh'''====

The <scene name='Sandbox_250/Ache_ach/24'>14 aromatic residues</scene> that line the active site gorge are Tyr70, Trp84, Trp120, Tyr121, Tyr130, Trp233, Trp279, Phe288, Phe290, Phe330, Phe331, Tyr334, Trp432 and Tyr442. These aromatic residues interact with the positively charged quaternary ammonium ion of ACh by virtue of cation-π interactions to filter it down the active-site gorge to the catalytic triad.

The AChE active site includes three residues that form a catalytic triad: <scene name='Sandbox_250/Ache_ach/20'>Ser200, Glu327, and His440</scene>. The <scene name='Sandbox_250/Ache_ach/28'>Catalytic Triad</scene>, highlithed in blue, is responsible for the hydrolysis of ACh into acetate and choline.