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Lqh-8/6 is a minor fraction isolated from the venom of the scorpion Leiurus quinquestriatus hebraeus. Here we describe the purification, amino acid sequencing and solution structure determination by NMR and molecular modeling of this peptide. Lqh-8/6 is a small polypeptide (38 residues) which contains 8 half-cystines and is highly similar to another venom component, chlorotoxin. Standard homonuclear methods were used to sequentially assign the proton NMR spectra and to collect spatial restraints for structure determination. Two populations, identified early in the assignment step, are in slow interconversion on the NMR timescale. The two conformers were shown to originate from a cis/trans peptidyl-prolyl isomerization. Using a distance geometry program and simulated annealing protocol under the NMR restraints we obtained 10 final structures for the major conformation (trans isomer). None of the structures showed NOE violations larger than 0.05 nm, and the rmsd value relative to the mean structure (considering the main chain atoms in well-defined secondary structure) is 0.07 nm. The three-dimensional structure contains a short a-helix strapped on a small antiparallel P-strand and an N-terminal extended fragment. The sequence/structure and structure/function relationships of the new scorpion toxin-like peptide are discussed in the context of the present structure determination. This toxin shows a stable, highly populated cis conformer of a peptidyl-prolyl peptide bond.

The complete amino acid sequence (325 residues) of sea urchin histone H2A has been established by structural studies of peptides derived from tryptic and chymotryptic cleavage of the maleylated protein and from thermolysin cleavage of the intact protein. By comparison with calf homologous histone, the basic amino-terminal and carboxy-terminal parts of the protein show 11 substitutions and 4 deletions. The remainder of the sequence, mostly hydrophobic, is almost completely unchanged.Among the five histones characterized in the chromatin of the eukaryotes, the histones H3 and H4 show a remarkable structural stability throughout the evolution [1,2] whereas the other histones present a structural variability, particularly accentuated in the histone H1.This variability first evidenced by comparative electrophoretic studies of whole histone from vertebrates [3] has been confirmed by sequence determinations [1,4-121. Recently, the primary structures of histone H2B1 and H2B2 from sperm of the sea urchin Parechinus angulosus have been reported [13,14]. The authors have shown that considerable variation occurred in the amino-terminal part of these proteins and that the hydrophobic carboxy-terminal region was almost completely invariable.In this paper, we report the primary structure of histone H2A from gonads of sea urchin Psammechinus miliaris. This amino acid sequence has been established from the data provided by tryptic and chymotryptic peptides of maleylated protein and by thermolysin peptides of intact protein. MATERIALS AND METHODS MaterialsTrypsin [treated with ~-(l-tosylamido-2-phenyl)-ethyl chloromethyl ketone] and chymotrypsin (premium quality WCDS) were purchased from Worthington. Carboxypeptidases A and B (treated with diisopropylphosphofluoridate) and thermolysin were purchased from Merck. Aminopeptidase M and carboxypeptidase C were obtained from Rohms and Haas.Phenylisothiocyanate, propan-1 -01 and dimethylallylamine were Sequanal grade from Pierce. Benzene and ethyl acetate for sequential analysis were purchased from S.D.S. (Peypin, France). Ethylmercaptan and propionic acid were obtained from Fluka. All other reagents were of the purest grade commercially available.