The venom of the funnel-web spider Agelenopsis aperta contains several peptides that paralyze prey by blocking voltage-sensitive calcium channels. Two peptides, omega-Aga-IVB (IVB) and omega-Aga-IVC (IVC), have identical amino acid sequences, yet have opposite absolute configurations at serine 46. These toxins had similar selectivities for blocking voltage-sensitive calcium channel subtypes but different potencies for blocking P-type voltage-sensitive calcium channels in rat cerebellar Purkinje cells as well as calcium-45 influx into rat brain synaptosomes. An enzyme purified from venom converts IVC to IVB by isomerizing serine 46, which is present in the carboxyl-terminal tail, from the L to the D configuration. Unlike the carboxyl terminus of IVC, that of IVB was resistant to the major venom protease. These results show enzymatic activities in A. aperta venom being used in an unprecedented strategy for coproduction of necessary neurotoxins that possess enhanced stability and potency.

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The solution structure of a peptide toxin isolated from funnel web spider venom, omega-Aga-IVB, was determined by 2D NMR methods. omega-Aga-IVB is a high-affinity specific blocker of P-type voltage-dependent calcium channels. Nearly all of the proton resonances of this 48-residue protein were assigned using conventional 2D homonuclear NMR experiments. The three-dimensional structure of the molecule was determined by simulated annealing. The distance and dihedral restraints used in the structure calculations were derived from NOESY and COSY-type experiments, respectively. Mass spectrometric analysis of omega-Aga-IVB suggests that the protein contains four disulfide bonds. In the absence of chemical data to identify the pattern of cysteine pairing, the disulfide bonds of the toxin are proposed from the NMR data and subsequent structural calculations. The structure of the toxin can be described as a three-stranded anti-parallel beta sheet connected by flexible loops. A striking feature of the structure is that the C-terminal 10 residues of this protein adopt random coil conformations. Several positively charged amino acid side chains are found localized on one face of the molecule, in close proximity to the C-terminal tail. This observation has led us to propose a speculative model of the toxins blockade mechanism.

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The synthesis and biological properties of a novel series of selective calcium-independent phosphodiesterase inhibitors are described. These compounds also inhibit the specific binding of [3H]rolipram to rat brain membranes and exhibit efficacy in preclinical models of antidepressant activity in mice, such as reducing immobility in the forced-swim test and reversing reserpine-induced hypothermia. Imidazolidinones 4 and 16 were found to be the most potent compounds studied.