Divergence in primary structure between the molecular forms of acetylcholinesterase

• Published in: The Journal of biological chemistry Vol. 263; no. 3; pp. 1140 - 1145
• Main Authors: Gibney, G, MacPhee-Quigley, K, Thompson, B, Vedvick, T, Low, M G, Taylor, S S, Taylor, P
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 25.01.1988; American Society for Biochemistry and Molecular Biology
• Subjects: acetylcholinesterase; Acetylcholinesterase - analysis; Amino Acid Sequence; Amino Acids - analysis; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Carbohydrate Conformation; Centrifugation, Density Gradient; Chromatography, High Pressure Liquid; electric organs; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Hydrolases; Molecular Sequence Data; Peptide Mapping; Solubility; Torpedo californica; Type C Phospholipases - metabolism; Vertebrata; Molecular form; Pisces; Animal; Torpedo californica; Primary structure; Acetylcholinesterase
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)57277-5

We have isolated a COOH-terminal tryptic peptide from the hydrophobic globular (5.6 S) form of Torpedo californica acetylcholinesterase that exhibits divergence in amino acid sequence from the catalytic subunit of the dimensionally asymmetric (17 S + 13 S) enzyme. The divergent peptide could be recovered from the glycophospholipid-modified 5.6 S enzyme only after treatment with phosphatidylinositol-specific phospholipase C. Upon reduction, carboxymethylation with [14C]iodoacetate, and trypsin digestion the resultant peptides were purified by gel filtration followed by high performance liquid chromatography. The high performance liquid chromatography profiles of 14C-labeled cysteine peptides from lipase-treated 5.6 S enzyme revealed unique radioactive peaks which had not been present in digests of the asymmetric form. These peaks all yielded identical amino acid sequences. The difference in chromatographic behavior of the individual peptides most likely reflects heterogeneity in post-translational processing. Gas-phase sequencing and composition analysis are consistent with the sequence: Leu-Leu-Asn-Ala-Thr-Ala-Cys. Composition includes 2-3 mol each of glucosamine and ethanolamine which is indicative of modification by glycophospholipid. Glucosamine is also present in an asparagine-linked oligosaccharide. The two forms of acetylcholinesterase diverge after the threonine residue within this peptide sequence; the hydrophobic form terminates with cysteine whereas the asymmetric form extends for 40 residues beyond the divergence. The locus of divergence and absence of any other amino acid sequence difference suggest that the molecular forms of acetylcholinesterase arise from a single gene by alternative mRNA processing.