Agelenin is a 35-amino acid peptide isolated from the venom of the spider Agelena opulenta, characterized by a C-terminal amide form and three disulfide bonds linking Cys3-19, Cys10-24, and Cys18-34. It functions as a presynaptic calcium channel blocker, with a three-dimensional structure featuring a short antiparallel β-sheet and four β-turns that align key residues (Phe9, Ser28, Arg33) similarly to the pharmacophore of insect channel inhibitors. This structural homology supports its application in neurobiology research, particularly for studying insect-specific calcium channel inhibition and ion channel structure-function relationships.