Polyethylene glycol (PEG) is a polyether compound with many applications from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular weight. The structure of PEG is commonly expressed as H-(O-CH2-CH2)n-OH. The numbers that are often included in the names of PEGs indicate their average molecular weights (e.g. a PEG with n = 9 would have an average molecular weight of approximately 400 daltons, and would be labeled PEG 400.) PEG-200 n =4 190 - 210 g/mol
Search PubMed for references concerning: PEG-SH-350
Title: A neutral molecule in a cation-binding site: specific binding of a PEG-SH to acetylcholinesterase from Torpedo californica Koellner G, Steiner T, Millard CB, Silman I, Sussman JL Ref: Journal of Molecular Biology, 320:721, 2002 : PubMed
The crystal structure of acetylcholinesterase from Torpedo californica complexed with the uncharged inhibitor, PEG-SH-350 (containing mainly heptameric polyethylene glycol with a terminal thiol group) is determined at 2.3 A resolution. This is an untypical acetylcholinesterase inhibitor, since it lacks the cationic moiety typical of the substrate (acetylcholine). In the crystal structure, the elongated ligand extends along the whole of the deep and narrow active-site gorge, with the terminal thiol group bound near the bottom, close to the catalytic site. Unexpectedly, the cation-binding site (formed by the faces of aromatic side-chains) is occupied by CH(2) groups of the inhibitor, which are engaged in C-H...pi interactions that structurally mimic the cation-pi interactions made by the choline moiety of acetylcholine. In addition, the PEG-SH molecule makes numerous other weak but specific interactions of the C-H...O and C-H...pi types.
Title: Active-site gorge and buried water molecules in crystal structures of acetylcholinesterase from Torpedo californica Koellner G, Kryger G, Millard CB, Silman I, Sussman JL, Steiner T Ref: Journal of Molecular Biology, 296:713, 2000 : PubMed
Buried water molecules and the water molecules in the active-site gorge are analyzed for five crystal structures of acetylcholinesterase from Torpedo californica in the resolution range 2.2-2.5 A (native enzyme, and four inhibitor complexes). A total of 45 buried hydration sites are identified, which are populated with between 36 and 41 water molecules. About half of the buried water is located in a distinct region neighboring the active-site gorge. Most of the buried water molecules are very well conserved among the five structures, and have low displacement parameters, B, of magnitudes similar to those of the main-chain atoms of the central beta-sheet structure. The active-site gorge of the native enzyme is filled with over 20 water molecules, which have poor hydrogen-bond coordination with an average of 2.9 polar contacts per water molecule. Upon ligand binding, distinct groups of these water molecules are displaced, whereas the others remain in positions similar to those that they occupy in the native enzyme. Possible roles of the buried water molecules are discussed, including their possible action as a lubricant to allow large-amplitude fluctuations of the loop structures forming the gorge wall. Such fluctuations are required to facilitate traffic of substrate, products and water molecules to and from the active-site. Because of their poor coordination, the gorge water molecules can be considered as "activated" as compared to bulk water. This should allow their easy displacement by incoming substrate. The relatively loose packing of the gorge water molecules leaves numerous small voids, and more efficient space-filling by substrates and inhibitors may be a major driving force of ligand binding.
