title: A molecular mechanism for Lys49-phospholipase A2 activity based on ligand-induced conformational change.
abstract: Agkistrodon contortrix laticinctus myotoxin is a Lys(49)-phospholipase A(2) (EC 3.1.1.4) isolated from the venom of the serpent A. contortrix laticinctus (broad-banded copperhead). We present here three monomeric crystal structures of the myotoxin, obtained under different crystallization conditions. The three forms present notable structural differences and reveal that the presence of a ligand in the active site (naturally presumed to be a fatty acid) induces the exposure of a hydrophobic surface (the hydrophobic knuckle) toward the C terminus. The knuckle in A. contortrix laticinctus myotoxin involves the side chains of Phe(121) and Phe(124) and is a consequence of the formation of a canonical structure for the main chain within the region of residues 118-125. Comparison with other Lys(49)-phospholipase A(2) myotoxins shows that although the knuckle is a generic structural motif common to all members of the family, it is not readily recognizable by simple sequence analyses. An activation mechanism is proposed that relates fatty acid retention at the active site to conformational changes within the C-terminal region, a part of the molecule that has long been associated with Ca(2+)-independent membrane damaging activity and myotoxicity. This provides, for the first time, a direct structural connection between the phospholipase "active site" and the C-terminal "myotoxic site," justifying the otherwise enigmatic conservation of the residues of the former in supposedly catalytically inactive molecules.
authors.affiliation: Centro de Biotecnologia Molecular Estrutural, Instituto de Física de São Carlos, USP, São Carlos-SP CEP 13560-970, Brazil.
authors.forename: Andre L B
authors.initials: AL
authors.lastname: Ambrosio
authors.forename: M Cristina
authors.initials: MC
authors.lastname: Nonato
authors.forename: Heloísa S Selistre
authors.initials: HS
authors.lastname: de Araújo
authors.forename: Raghuvir
authors.initials: R
authors.lastname: Arni
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Ward
authors.forename: Charlotte L
authors.initials: CL
authors.lastname: Ownby
authors.forename: Dulce H F
authors.initials: DH
authors.lastname: de Souza
authors.forename: Richard C
authors.initials: RC
authors.lastname: Garratt
mesh_terms: D000818:Animals; D001665:Binding Sites; D017124:Conserved Sequence; D003435:Crotalid Venoms / Q000201:enzymology*; D003460:Crystallization / Q000379:methods; D018360:Crystallography, X-Ray; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D008239:Lysine; D010741:Phospholipases A / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D040681:Structural Homology, Protein
chemical_list: C031442:Agkistrodon venoms; D003435:Crotalid Venoms; D005227:Fatty Acids; D008024:Ligands; D010741:Phospholipases A; D008239:Lysine