A unique hydrophobic domain of rat brain globular acetylcholinesterase for binding to cell membranes

Both salt-soluble and detergent-soluble rat brain globular acetylcholinesterases (SS- and DS- AChE EC 3.1.1.7) are amphiphiles, as shown by detergent dependency of enzymatic activity and binding to liposomes. Proteinase K and papain treatment transformed SS-AChE and DS-AChE into forms that, in absence of detergent, no longer aggregated nor bound to liposomes. In contrast, phosphatidylinositol-specific phospholipase C had no effect on these properties. Labeling DS-AChE with 3-(trifluoromethyl)-3-(m-(¹²⁵I)-iodophenyl) diazirine (¹²⁵I]TID) revealed, by polyacrylamide gel electrophoresis under reducing conditions, one single band of 69 kD apparent molecular mass. The same pattern was previously obtained with Bolton and Hunter reagent-labeled enzyme (1). Proteinase K treatment transformed the 11 S ¹²⁵I]TID labeled AChE into a 4 S form which no longer showed¹²⁵I-radioactivity and was unable to bind to liposomes. These results are compatible with the existence of a hydrophobic segment present both on salt-soluble and detergent-soluble 11 S AChE as well as on the minor forms 4 S and 7 S. This segment is not linked to the catalytic subunits by disulfide bounds in contrast to the 20 kD non-catalytic subunit described by Inestrosa et al. (2).Abbreviations used AChE acetylcholinesterase - SS-AChE salt-soluble AChE - DS-AChE detergent-soluble AChE - BSA bovine serum albumin - ChE serum (butyryl) cholinesterase - ConA-Sepharose concanavalin A-Sepharose 4B - DMAEBA-Sepharose dimethylaminoethylbenzoic acid-Sepharose 4B - PC-Chol-SA liposomes phosphatidylcholine-cholesterol-stearylamine liposomes - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis - ¹²⁵I-TID 3-(trifluoromethyl)-3-(m-(¹²⁵I)-iodophenyl) diazirine