Acetylcholinesterase

III. Structure

     One of the most studied forms of AChE comes from the electric fish, Torpedo californica.  The AChE monomer is composed of 537 residues with dimensions of approximately 45A x 60A x 65A (2).  In Torpedo, the major form of AChE is a homodimer.  It belongs to the class of  alpha/beta proteins and consists of a 12 stranded central mixed beta sheet surrounded by 14 alpha helices.  Push here to see the secondary structures    In order to view the 12 stranded beta sheet push here  The first and last pairs of strands each form beta hairpin loops (5). To see one of these loops push here . Strands 4-8 show the common right handed beta/loop/beta structure.  Overall, the strands are arranged in a slightly convex form.  There are two helices on their concave side and four on the convex side to completely sandwich the beta sheet.  The remaining helices loop around the sheet.  To view the alpha helices alone push here.   The AChE homodimer also contains a four helix bundle which functions to hold it together(5).

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