Journal:Protein Science:1
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Structural and functional characterization of the interaction of the photosensitizing probe methylene blue with Torpedo californica acetylcholinesterase
Aviv Paz, Esther Roth, Yacov Ashani, Yechun Xu, Valery L. Shnyrov, Joel L. Sussman, Israel Silman, and Lev Weiner[1]
Molecular Tour
The photosensitizer, methylene blue (MB), generates singlet oxygen that irreversibly inhibits Torpedo californica acetylcholinesterase (TcAChE). In the dark, it inhibits reversibly.
The TcAChE active site consists of two binding subsites. One of them is the "catalytic anionic site" (CAS), which involves the catalytic triad Ser200, His440, and Glu327 (colored orange) and the conserved residues Trp84 and Phe330 which also participate in ligand recognition. Another conserved residue Trp279 (colored cyan) is situated at the second binding subsite, termed the "peripheral anionic site" (PAS), ~14 Å from CAS. Thioflavin T (2j3q) is a good example of the PAS-binding AChE inhibitors. Superposition of the structure of known CAS-binding inhibitor edrophonium/TcAChE (2ack) on the thioflavin T/TcAChE complex structure (2j3q) shows that these ligands' positions do not overlap[2] [3].
MB is a noncompetitive inhibitor of TcAChE, competing with reversible inhibitors directed at both ‘‘anionic’’ subsites, but a single site is involved in inhibition. The crystal structure reveals a single MB stacked against Trp279 in the PAS, oriented down the gorge toward the CAS (2w9i); it is plausible that irreversible inhibition is associated with photooxidation of this residue and others within the active-site gorge. Superposition of the PAS regions of the MB/TcAChE and thioflavin T/TcAChE complexes reveals their similarity.
- ↑ Paz A, Roth E, Ashani Y, Xu Y, Shnyrov VL, Sussman JL, Silman I, Weiner L. Structural and functional characterization of the interaction of the photosensitizing probe methylene blue with Torpedo californica acetylcholinesterase. Protein Sci. 2012 Jun 1. doi: 10.1002/pro.2101. PMID:22674800 doi:10.1002/pro.2101
- ↑ Ravelli RB, Raves ML, Ren Z, Bourgeois D, Roth M, Kroon J, Silman I, Sussman JL. Static Laue diffraction studies on acetylcholinesterase. Acta Crystallogr D Biol Crystallogr. 1998 Nov 1;54(Pt 6 Pt 2):1359-66. PMID:10089512
- ↑ Harel M, Sonoda LK, Silman I, Sussman JL, Rosenberry TL. Crystal structure of thioflavin T bound to the peripheral site of Torpedo californica acetylcholinesterase reveals how thioflavin T acts as a sensitive fluorescent reporter of ligand binding to the acylation site. J Am Chem Soc. 2008 Jun 25;130(25):7856-61. Epub 2008 May 31. PMID:18512913 doi:https://dx.doi.org/10.1021/ja7109822
