title: Biophysical studies suggest a new structural arrangement of crotoxin and provide insights into its toxic mechanism.
abstract: Crotoxin (CTX) is the main neurotoxin found in Crotalus durissus rattlesnake venoms being composed by a nontoxic and non-enzymatic component (CA) and a toxic phospholipase A2(CB). Previous crystallographic structures of CTX and CB provided relevant insights: (i) CTX structure showed a 1:1 molecular ratio between CA and CB, presenting three tryptophan residues in the CA/CB interface and one exposed to solvent; (ii) CB structure displayed a tetrameric conformation. This study aims to provide further information on the CTX mechanism of action by several biophysical methods. Our data show that isolated CB can in fact form tetramers in solution; however, these tetramers can be dissociated by CA titration. Furthermore, CTX exhibits a strong reduction in fluorescence intensity and lifetime compared with isolated CA and CB, suggesting that all tryptophan residues in CTX may be hidden by the CA/CB interface. By companying spectroscopy fluorescence and SAXS data, we obtained a new structural model for the CTX heterodimer in which all tryptophans are located in the interface, and the N-terminal region of CB is largely exposed to the solvent. Based on this model, we propose a toxic mechanism of action for CTX, involving the interaction of N-terminal region of CB with the target before CA dissociation.
authors.affiliation: Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, UNESP, Botucatu-SP, Brazil.
authors.forename: Carlos A H
authors.initials: CA
authors.lastname: Fernandes
authors.affiliation: Departamento de Física, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, USP, Ribeirão Preto-SP, Brazil.
authors.forename: Wallance M
authors.initials: WM
authors.lastname: Pazin
authors.affiliation: Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, UNESP, Botucatu-SP, Brazil.
authors.forename: Thiago R
authors.initials: TR
authors.lastname: Dreyer
authors.affiliation: Departamento de Física Experimental, Instituto de Física, Universidade de São Paulo - USP, São Paulo, SP, Brazil.
authors.forename: Renata N
authors.initials: RN
authors.lastname: Bicev
authors.affiliation: Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, UNESP, Botucatu-SP, Brazil.|Departamento de Farmacologia, Instituto de Ciências Biológicas, UFMG, Belo Horizonte, MG, Brazil.
authors.forename: Walter L G
authors.initials: WL
authors.lastname: Cavalcante
authors.affiliation: Diretoria de Pesquisa e Desenvolvimento, Fundação Ezequiel Dias (FUNED), Belo Horizonte, MG, Brazil.
authors.forename: Consuelo L
authors.initials: CL
authors.lastname: Fortes-Dias
authors.affiliation: Departamento de Física, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, USP, Ribeirão Preto-SP, Brazil.
authors.forename: Amando S
authors.initials: AS
authors.lastname: Ito
authors.affiliation: Departamento de Física Experimental, Instituto de Física, Universidade de São Paulo - USP, São Paulo, SP, Brazil.
authors.forename: Cristiano L P
authors.initials: CL
authors.lastname: Oliveira
authors.affiliation: Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, UNESP, Botucatu-SP, Brazil.
authors.forename: Roberto Morato
authors.initials: RM
authors.lastname: Fernandez
authors.affiliation: Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, UNESP, Botucatu-SP, Brazil.
authors.forename: Marcos R M
authors.initials: MR
authors.lastname: Fontes
mesh_terms: D055592:Biophysical Phenomena; D003439:Crotoxin / Q000737:chemistry* / Q000633:toxicity*; D008958:Models, Molecular; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D053838:Scattering, Small Angle; D013050:Spectrometry, Fluorescence
chemical_list: D003439:Crotoxin