title: A molecular dynamics investigation of mono and dimeric states of the outer membrane enzyme OMPLA.
abstract: OMPLA is a phospholipase found in the outer membranes of many Gram-negative bacteria. Enzyme activation requires calcium-induced dimerisation plus bilayer perturbation. As the conformation of OMPLA in the different crystal forms (monomer versus dimer; with/without bound Ca(2+)) is remarkably similar we have used multi-nanosecond molecular dynamics (MD) simulations to probe possible differences in conformational dynamics that may be related to enzyme activation. Simulations of calcium-free monomeric OMPLA, of the Ca(2+)-bound dimer, and of the Ca(2+)-bound dimer with a substrate analogue covalently linked to the active site serine have been performed, all with the protein embedded in a phospholipid (POPC) bilayer. All simulations were stable, but differences in the dynamic behaviour of the protein between the various states were observed. In particular, the stability of the active site and the hydrophobic substrate-binding cleft varied. Dimeric OMPLA is less flexible than monomeric OMPLA, especially around the active site. In the absence of bound substrate analogue, the hydrophobic substrate-binding cleft of dimeric OMPLA collapses. A model is proposed whereby the increased stability of the active site in dimeric OMPLA is a consequence of the local ordering of water around the nearby calcium ion. The observed collapse of the substrate-binding cleft may explain the experimentally observed occurrence of multiple dimer conformations of OMPLA, one of which is fully active while the other shows significantly reduced activity.
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road Oxford, OX1 3QU, UK.
authors.forename: Marc
authors.initials: M
authors.lastname: Baaden
authors.forename: Christoph
authors.initials: C
authors.lastname: Meier
authors.forename: Mark S P
authors.initials: MS
authors.lastname: Sansom
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry*; D001665:Binding Sites; D002118:Calcium; D003198:Computer Simulation; D019281:Dimerization; D004789:Enzyme Activation; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers; D008958:Models, Molecular; D010713:Phosphatidylcholines; D010741:Phospholipases A / Q000737:chemistry*; D054466:Phospholipases A1; D011487:Protein Conformation
chemical_list: D001425:Bacterial Outer Membrane Proteins; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010741:Phospholipases A; D054466:Phospholipases A1; C412876:outer membrane phospholipase A; D002118:Calcium; C028694:1-palmitoyl-2-oleoylphosphatidylcholine