title: Crystallographic and spectroscopic characterization of a molecular hinge: conformational changes in bothropstoxin I, a dimeric Lys49-phospholipase A2 homologue.
abstract: Bothropstoxin I (BthTX-I) from the venom of Bothrops jararacussu is a myotoxic phospholipase A2 (PLA2) homologue which, although catalytically inactive due to an Asp49-->Lys substitution, disrupts the integrity of lipid membranes by a Ca2+-independent mechanism. The crystal structures of two dimeric forms of BthTX-I which diffract X-rays to resolutions of 3.1 and 2.1 angstroms have been determined. The monomers in both structures are related by an almost perfect twofold axis of rotation and the dimer interfaces are defined by contacts between the N-terminal alpha-helical regions and the tips of the beta-wings of partner monomers. Significant differences in the relative orientation of the monomers in the two crystal forms results in "open" and "closed" dimer conformations. Spectroscopic investigations of BthTX-I in solution have correlated these conformational differences with changes in the intrinsic fluorescence emission of the single tryptophan residues located at the dimer interface. The possible relevance of this structural transition in the Ca2+-independent membrane damaging activity is discussed.
authors.affiliation: Institute of Physics (IFSC), USP, São Carlos-SP, Brazil.
authors.forename: M T
authors.initials: MT
authors.lastname: da Silva Giotto
authors.forename: R C
authors.initials: RC
authors.lastname: Garratt
authors.forename: G
authors.initials: G
authors.lastname: Oliva
authors.forename: Y P
authors.initials: YP
authors.lastname: Mascarenhas
authors.forename: J R
authors.initials: JR
authors.lastname: Giglio
authors.forename: A C
authors.initials: AC
authors.lastname: Cintra
authors.forename: W F
authors.initials: WF
authors.lastname: de Azevedo
authors.forename: R K
authors.initials: RK
authors.lastname: Arni
authors.forename: R J
authors.initials: RJ
authors.lastname: Ward
mesh_terms: D000818:Animals; D017837:Bothrops; D003435:Crotalid Venoms / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D008239:Lysine / Q000737:chemistry; D010741:Phospholipases A / Q000737:chemistry*; D054467:Phospholipases A2; D011487:Protein Conformation; D013057:Spectrum Analysis
chemical_list: D003435:Crotalid Venoms; C078097:bothropstoxin; D010741:Phospholipases A; D054467:Phospholipases A2; D008239:Lysine