RESUMO
Disulfide-bound dimers of three-fingered toxins have been discovered in the Naja kaouthia cobra venom; that is, the homodimer of alpha-cobratoxin (a long-chain alpha-neurotoxin) and heterodimers formed by alpha-cobratoxin with different cytotoxins. According to circular dichroism measurements, toxins in dimers retain in general their three-fingered folding. The functionally important disulfide 26-30 in polypeptide loop II of alpha-cobratoxin moiety remains intact in both types of dimers. Biological activity studies showed that cytotoxins within dimers completely lose their cytotoxicity. However, the dimers retain most of the alpha-cobratoxin capacity to compete with alpha-bungarotoxin for binding to Torpedo and alpha7 nicotinic acetylcholine receptors (nAChRs) as well as to Lymnea stagnalis acetylcholine-binding protein. Electrophysiological experiments on neuronal nAChRs expressed in Xenopus oocytes have shown that alpha-cobratoxin dimer not only interacts with alpha7 nAChR but, in contrast to alpha-cobratoxin monomer, also blocks alpha3beta2 nAChR. In the latter activity it resembles kappa-bungarotoxin, a dimer with no disulfides between monomers. These results demonstrate that dimerization is essential for the interaction of three-fingered neurotoxins with heteromeric alpha3beta2 nAChRs.
Assuntos
Proteínas Neurotóxicas de Elapídeos/química , Proteínas Neurotóxicas de Elapídeos/metabolismo , Dissulfetos/química , Dissulfetos/metabolismo , Animais , Cromatografia em Gel , Cromatografia Líquida de Alta Pressão , Dicroísmo Circular , Proteínas Neurotóxicas de Elapídeos/isolamento & purificação , Dimerização , Elapidae , Humanos , Modelos Moleculares , Estrutura Terciária de Proteína , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por MatrizAssuntos
Epilepsia do Lobo Frontal/tratamento farmacológico , Epilepsia do Lobo Frontal/genética , Neurônios/fisiologia , Receptores Nicotínicos/genética , Receptores Nicotínicos/fisiologia , Animais , Carbamazepina/farmacologia , Epilepsia do Lobo Frontal/fisiopatologia , Expressão Gênica/efeitos dos fármacos , Humanos , Ligantes , Modelos Biológicos , Mutação , Nicotina/farmacologia , Receptores Nicotínicos/efeitos dos fármacosRESUMO
Mal de Meleda is an autosomal recessive inflammatory and keratotic palmoplantar skin disorder due to mutations in the ARS B gene, encoding for SLURP-1 (secreted mammalian Ly-6/uPAR-related protein 1). SLURP-1 belongs to the Ly-6/uPAR superfamily of receptor and secreted proteins, which participate in signal transduction, immune cell activation or cellular adhesion. The high degree of structural similarity between SLURP-1 and the three fingers motif of snake neurotoxins and Lynx1 suggests that this protein interacts with the neuronal acetylcholine receptors. We found that SLURP-1 potentiates the human alpha 7 nicotinic acetylcholine receptors that are present in keratinocytes. These results identify SLURP-1 as a secreted epidermal neuromodulator which is likely to be essential for both epidermal homeostasis and inhibition of TNF-alpha release by macrophages during wound healing. This explains both the hyperproliferative as well as the inflammatory clinical phenotype of Mal de Meleda.