AChE bivalent inhibitors

From Proteopedia

Revision as of 10:02, 31 May 2009

PART I. Tacrine- and hupyridone-containing compounds

This page is a continuation of the pages AChE inhibitors and substrates and AChE inhibitors and substrates (Part II).

• 1zgb Complex with (R)-tacrine-(10)-hupyridone (cmp R-3)
• 1zgc Complex with (S)-tacrine-(10)-hupyridone (cmp S-3)
• 1acj Complex with tacrine alone
• 1h22 Complex with (S,S)-(-)-Bis(12)-hupyridone (cmp (S,S)-(-)-4b)
• 1h23 Complex with (S,S)-(-)-Bis(10)-hupyridone (cmp (S,S)-(-)-4a)
• 2cmf Complex with Bis(5)-tacrine derivative (cmp 2d)
• 2ckm Complex with Bis(7)-tacrine derivative (cmp 2f)
• 1ut6 Complex with N-9-(1',2',3',4'-TETRAHYDROACRIDINYL)-1,8-DIAMINOOCTANE (cmp 6)
• 1odc Complex with cmp 7

The of TcAChE consists of two binding subsites. One of them is the "catalytic anionic site" (CAS), which contains the catalytic triad (colored orange) and the conserved residues and which participate in ligand recognition. Another conserved residue (colored cyan) is situated at a second binding subsite, termed the "peripheral anionic site" (PAS), ~14 Å from CAS. Therefore, ligands that can interact with both these subsites, are expected to be more potent AChE inhibitors than inhibitors interacting with CAS only. One of the ways to produce such ligands is to introduce two inhibitor moieties in one compound. If it is spatially required, these subunits could be separated by alkyl linker with suitable length. According to the strategy of the use of a bivalent ligand, the (RS)-(±)-tacrine-(10)-hupyridone ((R)-3 or (S)-3) was designed and synthesized. It consists of (colored magenta), 10-carbon (yellow), and (red). The tacrine moiety of this inhibitor binds at the CAS, the linker spans the gorge, and the hupyridone moiety binds at the PAS.

Shown is the overlap of the (R)-3/TcAChE and tacrine/TcAChE complexes at the . of the trigonal (R)-3/TcAChE structure (1zgb; (R)-3 colored cyan; TcAChE residues interacting with (R)-3 are colored sea-green) with the crystal structure of tacrine/TcAChE (1acj, (tacrine colored magenta; residues interacting with tacrine are colored pink) reveals a similar binding mode for the tacrine moiety. In both structures the tacrine ring is situated at the CAS, between the aromatic residues Trp84 and Phe330. Steric clash with the 10-carbon linker could explain the tilt observed for the Phe330 (yellow and transparent in the tacrine/TcAChE). Water molecules are shown as red spheres. The N atom of the tacrine moiety of (R)-3 forms a with His440 O (3.0 Å) similar to the one seen in the tacrine/TcAChE. The tacrine/TcAChE structure shows the system of three water molecules at the CAS where ((R)-3/TcAChE) binds the tacrine-linker N via hydrogen bonds to Ser81 O, Ser122 Oγ, and Asn85 Oδ1 (2.6-3.5 Å) .

The overlap of the (R)-3/TcAChE (1zgb) and bis-hupyridone/TcAChE complexes (1h22 and 1h23) at the is shown. of the TcAChE complexes of (R)-tacrine-(10)-hupyridone ((R)-3, cyan), (S,S)-(-)-Bis(12)-hupyridone ((S,S)-(-)-4b, orange, i.e. 12-carbon-tether-linked hupyridone dimer) and (S,S)-(-)-Bis(10)-hupyridone ((S,S)-(-)-4a, plum) demonstrates the binding mode of the hupyridone moiety. TcAChE residues of symmetry-related molecule are shown in magenta. X-ray structures of TcAChE complexed with these 10- and 12-carbon-tether-linked (S,S)-(-)-4a and (S,S)-(-)-4b show one moiety bound at the , the linker spanning the gorge, and the other moiety bound at the . There are two connecting the hupyridone O to Lys11 Nζ and hupyridone N to Gln185 Oε1 of a symmetry-related molecule in the (R)-3/TcAChE complex. Water molecules are shown as red spheres. Another hydrogen bond connects the hupyridone O to a water molecule, which is bound to Ser286 N. Similarly, the hupyridone moiety at the PAS site of both (-)-4a and (-)-4b complexes forms direct and water-mediated hydrogen bonds with the protein backbone.

The of (R)-3 (cyan) and (S)-3 (1zgc) bound to the TcAChE active site in the orthorhombic forms is shown. of (S,S)-(-)-4a (magenta) and (S)-3 (orange, orthorhombic TcAChE) demonstrates the similar mode of binding of the hupyridone unit at the PAS. The residues Trp279 (top) and Trp84 (bottom) represent the PAS and the CAS, respectively.

2d and 2f are bis(n)-tacrine derivatives with n=5 and 7 (number of carbons in the linkers), respectively. These compounds are more potent and selective AChE inhibitors than tacrine alone. The binding of the first tacrine moiety of at the TcAChE catalytic anionic site (CAS) is similar to that of tacrine alone (1acj). The second tacrine moiety of the 2d interacts with peripheral anionic site (PAS) near the Trp279. The interaction of 2d at CAS caused increase of the between Ser200 Oγ and H440 Nε2 atoms, and, therefore, disruption of the catalytic triad (Ser200, H220, E327) compared with the native structure (2ace). This binding results in in the Val281-Ser291 loop causing a significant change in the surface of the active-site gorge in comparison to the native structure (2ace). The first tacrine moiety of the compound 2f (heptylene-linked bis-tacrine, 2ckm) also adopts similar as tacrine alone and the first tacrine moiety of the 2d at the CAS. The second tacrine moiety of the 2f interacts with PAS near the Trp279, similar to 2d. The of the 2f does not cause significant structural changes in the TcAChE upon forming the complex in comparison to the native TcAChE structure. of the 2d and 2f reveals different contacts between the second tacrine moieties of these compounds and TcAChE. There are two additional structures of tacrine-containing AChE inhibitors: compounds (1ut6) and (1odc). The tacrine moieties of these compounds also adopt similar conformations and interactions with CAS as tacrine alone, 2f and 2d. Both inhibitors 6 and 7 are spanning the from the CAS up to the PAS, but since compound 7 lacks the second tacrine moiety, Trp279 adopts a different conformation in this complex structure. In the three structures: native (cyan), TcAChE-cmp 6 complex (white), and TcAChE-cmp 7 complex (crimson) , except of Trp279, all the other TcAChE active-site gorge residues have similar conformations.

For information about additional AChE inhibitors see page AChE bivalent inhibitors (Part II).

References

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• Harel M, Hyatt JL, Brumshtein B, Morton CL, Yoon KJ, Wadkins RM, Silman I, Sussman JL, Potter PM. The crystal structure of the complex of the anticancer prodrug 7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxycamptothecin (CPT-11) with Torpedo californica acetylcholinesterase provides a molecular explanation for its cholinergic action. Mol Pharmacol. 2005 Jun;67(6):1874-81. Epub 2005 Mar 16. PMID:15772291 doi:http://dx.doi.org/10.1124/mol.104.009944
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