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Structural modifications of the Ω loop in human acetylcholinesterase
Author(s) -
Velan Baruch,
Barak Dov,
Ariel Naomi,
Leitner Moshe,
Bino Tamar,
Ordentlich Arie,
Shafferman Avigdor
Publication year - 1996
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(96)00995-7
Subject(s) - chemistry , stereochemistry , acetylcholinesterase , allosteric regulation , moiety , residue (chemistry) , hydrolase , loop (graph theory) , protein structure , active site , lipase , indole test , enzyme , biophysics , biochemistry , biology , mathematics , combinatorics
Conformational mobility of the surface Ω loop (Cys‐69‐Cys‐96) in human acetylcholinesterase (HuAChE) was recently implicated in substrate accessibility to the active center and in the mechanism of allosteric modulation of enzymatic activity. We therefore generated and kinetically evaluated the following modifications or replacements in HuAChE: (a) residues at the loop ends, (b) residues involved in putative hydrogen‐bond interactions within the loop and between the loop and the protein core, (c) ChEs conserved proline residues within the loop and (d) a deletion of a conserved segment of 5 residues. All the residue replacements, including those of the prolines, had either limited or no effect on enzyme reactivity. These results suggest that unlike the case of lipase, the Ω loop in the HuAChE is not involved in large lid‐like displacements. In cases where modifications of the loop sequence had some effect on reactivity, the effects could be attributed to an altered position of residue Trp‐86 supporting the proposed coupling between the structure of the Ω loop and the positioning of the Trp‐86 indole moiety, in catalytic activity and in allosterism.