Study of structure-activity relationship of fasciculin by acetylation of amino groups.
Dendroaspis angusticeps (green mamba) has two toxins, fasciculins, that are non-competitive inhibitors of acetylcholinesterase. Amino groups of fasciculin 2 were acetylated with acetic anhydride. The monoacetyl derivatives of the epsilon-amino groups (Lys 25, 32, 51 and 58) retained between 28 and 43% of the initial activity and that of the alpha-amino group 72%. Acetylation of Lys 25 that has the most reactive amino group decreased the activity by 65% apparently without producing structural perturbations, since the circular dichroism spectrum was not affected. The three-dimensional structure shows a cationic cluster formed by Lys 32, 51, Arg 24 and 28. A comparison of 175 sequences of homologous toxins shows that Lys 32 is unique for fasciculin. Acetylation of lysine residues in the cluster had a large effect and reduced the activity by 72% (Lys 32) and 57% (Lys 51). This suggests an important role for the cationic cluster. Lys 25 together with Lys 32 and 51 were, therefore, assumed to be in the active site.
Cerveñanský
C
C
Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay.
Engström
A
A
Karlsson
E
E
D000107:Acetylation; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002942:Circular Dichroism; D004546:Elapid Venoms / Q000737:chemistry* / Q000302:isolation & purification; D008958:Models, Molecular; D008969:Molecular Sequence Data; D013329:Structure-Activity Relationship
D004546:Elapid Venoms; C044937:fasciculin