4dcf | pdb_00004dcf
Structure of MTX-II from Bothrops brazili
Structural highlights
Function[PA2H1_BOTBZ] Snake venom phospholipase A2 homolog that lacks enzymatic activity. Is myotoxic and displays edema-inducing activities in mouse paw (PubMed:18602430). Also displays cytotoxic activity against some cell lines, and antimicrobial activities against E.coli, C.albicans and Leishmania (PubMed:18602430). A model of myotoxic mechanism has been proposed: an apo Lys49-PLA2 is activated by the entrance of a hydrophobic molecule (e.g. fatty acid) at the hydrophobic channel of the protein leading to a reorientation of a monomer (PubMed:24145104). This reorientation causes a transition between 'inactive' to 'active' states, causing alignment of C-terminal and membrane-docking sites (MDoS) side-by-side and putting the membrane-disruption sites (MDiS) in the same plane, exposed to solvent and in a symmetric position for both monomers (PubMed:24145104). The MDoS region stabilizes the toxin on membrane by the interaction of charged residues with phospholipid head groups (PubMed:24145104). Subsequently, the MDiS region destabilizes the membrane with penetration of hydrophobic residues (PubMed:24145104). This insertion causes a disorganization of the membrane, allowing an uncontrolled influx of ions (i.e. calcium and sodium), and eventually triggering irreversible intracellular alterations and cell death (PubMed:24145104).[1] [2] Publication Abstract from PubMedCatalytically inactive phospholipase A(2) (PLA(2)) homologues play key roles in the pathogenesis induced by snake envenomation, causing extensive tissue damage via a mechanism still unknown. Although, the amino acid residues directly involved in catalysis are conserved, the substitution of Asp49 by Arg/Lys/Gln or Ser prevents the binding of the essential calcium ion and hence these proteins are incapable of hydrolyzing phospholipids. In this work, the crystal structure of a Lys49-PLA(2) homologue from Bothrops brazili (MTX-II) was solved in two conformational states: (a) native, with Lys49 singly coordinated by the backbone oxygen atom of Val31 and (b) complexed with tetraethylene glycol (TTEG). Interestingly, the TTEG molecule was observed in two different coordination cages depending on the orientation of the nominal calcium-binding loop and of the residue Lys49. These structural observations indicate a direct role for the residue Lys49 in the functioning of a catalytically inactive PLA(2) homologue suggesting a contribution of the active site-like region in the expression of pharmacological effects such as myotoxicity and edema formation. Despite the several crystal structures of Lys49-PLA(2) homologues already determined, their biological assembly remains controversial with two possible conformations. The extended dimer with the hydrophobic channel exposed to the solvent and the compact dimer in which the active site-like region is occluded by the dimeric interface. In the MTX-II crystal packing analysis was found only the extended dimer as a possible stable quaternary arrangement. Crystallographic portrayal of different conformational states of a Lys49 phospholipase A(2) homologue: Insights into structural determinants for myotoxicity and dimeric configuration.,Ullah A, Souza TA, Betzel C, Murakami MT, Arni RK Int J Biol Macromol. 2012 May 11. PMID:22584077[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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