Molecular structure of elongated forms of electric eel acetylcholinesterase

Lili Anglister*, Israel Silman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

89 Scopus citations

Abstract

Molecular forms of acetylcholinesterase extracted from fresh electric organ tissue of the electric eel are elongated structures in which a multi-subunit head is connected to a fibrous tail. The principal form, 18 S acetylcholinesterase, is of molecular weight approximately 1,050,000, contains about 12 catalytic subunits in its head, has a tail approximately 500 Å long, and aggregates reversibly at low ionic strength. Trypsin converts it to an 11 S globular tetramer devoid of the tail and lacking the capacity to aggregate in low-salt solutions. Amino acid analysis shows that elongated forms of acetylcholinesterase contain significant amounts of hydroxyproline and hydroxylysine, characteristic components of collagen, which are absent from 11 S acetylcholinesterase. Collagenase converts 18 S acetylcholinesterase to a 20 S form which no longer aggregates in low salt. Purified 20 S acetylcholinesterase has about half the hydroxyproline and hydroxylysine contents of the 18 S enzyme, and physicochemical measurements indicate the formation of a more symmetrical molecular structure without marked reduction in molecular weight. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis without reducing agent shows that in 18 S acetylcholinesterase half the catalytic subunits are present as dimers linked by disulfide bonds. The remaining subunits migrate as larger molecular species which contain significant amounts of hydroxylysine, are specifically modified by collagenase and are converted to dimers and monomers by trypsin. Sodium dodecyl sulfate/acrylamide gel electrophoresis with reducing agent reveals, in 18 S acetylcholinesterase, two polypeptides of molecular weights 45,000 and 47,000 which are absent in the 11 S tetramer. They are readily digested by collagenase under conditions which do not affect the catalytic subunits, with concomitant formation of a new 30,000 polypeptide. The above data can be rationalized by a model in which 18 S acetylcholinestorase contains three subunit tetramers, each linked by disulfides to one strand of a collagen triple helix. Sodium dodecyl sulfate detaches those subunit dimers which are not covalently linked to the tail; trypsin attacks the distal portion of the collagen triple helix releasing discrete tetramers, and collagenase specifically attacks the triple helix near its midpoint, producing a shortened structure in which the residual tail still holds the tetramers together, but destroying the capacity for self-association at low ionic strength. This latter property may be related to the postulated role of the tail in anchoring acetylcholinesterase to the fibrillar matrix of the basement membrane.

Original languageAmerican English
Pages (from-to)293-311
Number of pages19
JournalJournal of Molecular Biology
Volume125
Issue number3
DOIs
StatePublished - 5 Nov 1978
Externally publishedYes

Bibliographical note

Funding Information:
This research ~vass upported by grants from t,he Muscular Dystroplly Associatiolls of America, t,hr United States Israel Bina.tional Science Follndatiorr and the Israel Com-lnittw for Basic Research. We thank Mrs Esther Roth for expert technical assistaricr. Dr Yaditi Dudai for his participation in some of the early oxprriments, and Dr Sara Fuclls, Dr Shmaryahu Blumberp. Dr Yadin Dudai and Dr Vivian ‘l’eichherq for ttlcsil critical readirlg of the manuscript.

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