The 2.5-A crystal structure of the calcium-free form of the dimeric venom phospholipase A2 from the Western Diamondback rattlesnake Crotalus atrox, has been refined to an R-factor of 17.8% (I greater than 2 sigma) and acceptable stereochemistry. The molecule is a nearly perfect 2-fold symmetric dimer in which most of the catalytic residues of both subunits face an internal cavity ...
The 2.5-A crystal structure of the calcium-free form of the dimeric venom phospholipase A2 from the Western Diamondback rattlesnake Crotalus atrox, has been refined to an R-factor of 17.8% (I greater than 2 sigma) and acceptable stereochemistry. The molecule is a nearly perfect 2-fold symmetric dimer in which most of the catalytic residues of both subunits face an internal cavity. The restricted access to the putative catalytic sites is especially puzzling as the optimal substrates for this and most other phospholipase A2 are phospholipids condensed in micellar or lamellar aggregates. We point out that substrate access to the internal cavity may be aided by calcium binding which can alter the intersubunit contacts that shield the catalytic network. We also suggest that a system of hydrogen-bonded moieties exists on the surface of the dimer that links the amino terminus to the catalytic system, through an invariant Gln 4 side chain and the backbone of the active center residue, Tyr 73. This hydrogen-bonded network is on a highly accessible surface of the dimer and would appear to contribute to the enzyme's (as opposed to the proenzyme's) special capacity to attack aggregated rather than monomeric substrate.
Related Citations:
A Comparison of the Crystal Structures of Phospholipase A2 from Bovine Pancreas and Crotalus Atrox Venom Renetseder, R., Brunie, S., Dijkstra, B.W., Drenth, J., Sigler, P.B. (1985) J Biol Chem 260: 11627
The 2.5 Angstroms Crystal Structure of a Dimeric Phospholipase A2 from the Venom of Crotalus Atrox Keith, C., Feldman, D.S., Deganello, S., Glick, J., Ward, K.B., Jones, E.O., Sigler, P.B. (1981) J Biol Chem 256: 8602
Characterization of Crystals of Two Venom Phospholipases A2 Pasek, M., Keith, C., Feldman, D., Sigler, P.B. (1975) J Mol Biol 97: 395
Organizational Affiliation:
Department of Chemistry and Biochemistry, Baylor University, Waco, TX, 76798, USA. Electronic address: JungHyun_Min@baylor.edu.
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