Isolation and molecular characterization of LVP1 lipolysis activating peptide from scorpion Buthus occitanus tunetanus

LVP1, a novel protein inducing lipolytic response in adipose cells, was purified from scorpion Buthus occitanus tunetanus venom. It represented 1% of crude venom proteins, with pHi∼6 and molecular mass of 16 170 Da. In contrast to well-characterized scorpion toxins, reduction and alkylation of LVP1 revealed an heterodimeric structure. Isolated α and β chains of LVP1 have a respective molecular mass of 8877 and 8807 Da as determined by mass spectrometry. The N-terminal and some internal peptide sequences of LVP1α and β were determined by Edman degradation. The full amino acid sequences of both chains were deduced from nucleotide sequences of the corresponding cDNAs prepared based on peptide sequences and the 3′ and 5′ RACE methodologies. LVP1α and β cDNAs encode a signal peptide of 22 residues and a mature peptide of 69 and 73 residues, respectively. Each mature peptide contains seven cysteines, which are compatible with an interchain disulfide bridge. The cDNA deduced protein structures share a high similarity with those of some Na+ channel scorpion toxins. LVP1 was not toxic to mice after intracerebro-ventricular injection. LVP1 stimulated lipolysis on freshly dissociated rat adipocytes in a dose-dependent manner with EC50 of ∼1+0.5 μg/ml. LVP1 subunits did not display any lipolytic activity. As previously described for venom, β adrenergic receptor (β AR) antagonists interfere with LVP1 activity. Furthermore, it is shown that LVP1 competes with [3H]-CGP 12177 (β1/β2 antagonist) for binding to adipocyte plasma membrane with an IC50 of about 10−7 M. These results demonstrate the existence of a new type of scorpion venom nontoxic peptides that are structurally related to Na+ channel toxins but can exert a distinct biological activity on adipocyte lipolysis through a β-type adrenoreceptor pathway.