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A sperm motility inhibitor isolated from porcine seminal plasma is identical to porcine β-microseminoprotein (MSP). Circular dichroism (CD) and nuclear magnetic resonance (NMR) data showed that the native and recombinant porcine MSPs exhibit very similar structure. The five disulfide pairings on porcine MSP were unambiguously assigned based on NMR data and further confirmed using structural calculations. Surprisingly, our derived pairings differ from those recently reported for ostrich MSP based on matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) analysis. Furthermore, the secondary structure was determined to comprise one four-stranded and two double-stranded antiparallel β-sheets. As we know, this is the first detailed secondary structure reported among several types of MSPs. [Copyright &y& Elsevier]

A new K+-channel blocking peptide identified from the scorpion venom of Tityus cambridgei (Tc1) is composed of 23 amino acid residues linked with three disulfide bridges. Tc1 is the shortest known toxin from scorpion venom that recognizes the Shaker B K+ channels and the voltage-dependent K+ channels in the brain. Synthetic Tc1 was produced using solid-phase synthesis, and its activity was found to be the same as that of native Tc1. The pairings of three disulfide bridges in the synthetic Tc1 were identified by NMR experiments. The NMR solution structures of Tc1 were determined by simulated annealing and energy-minimization calculations using the X-PLOR program. The results showed that Tc1 contains an α-helix and a 310-helix at N-terminal Gly4-Lys10 and a double-stranded β-sheet at Gly13-Ile16 and Arg19-Tyr23, with a type I′ β-turn at Asn17-Gly18. Superposition of each structure with the best structure yielded an average root mean square deviation of 0.26 ± 0.05 Å for the backbone atoms and of 1.40 ± 0.23 Å for heavy atoms in residues 2 to 23. The three-dimensional structure of Tc1 was compared with two structurally and functionally related scorpion toxins, charybdotoxin (ChTx) and noxiustoxin (NTx). We concluded that the C-terminal structure is the most important region for the blocking activity of voltage-gated (Kv-type) channels for scorpion K+-channel blockers. We also found that some of the residues in the larger scorpion K+-channel blockers (31 to 40 amino acids) are not involved in K+-channel blocking activity. [ABSTRACT FROM AUTHOR]