THE CRYSTAL STRUCTURE OF OUTER MEMBRANE PHOSPHOLIPASE, AN INTEGRAL MEMBRANE ENZYME.
H.J. Snijder, N. Dekker, I. Ubarretxena, M. Blaauw, K.H. Kalk, H.M. Verheij and B.W. Dijkstra.
University of Groningen, Nijenborgh 4, 9747
AG Groningen, The Netherlands
University of Utrecht, Padualaan 8, 3584
CH Utrecht, The Netherlands
Keywords: crystal structure, membrane
enzyme, phospholipase, dimerisation
The gene encoding for outer membrane phospholipase A (OMPLA) is wide spread among enterobacteriaceae, of which many are pathogenic. OMPLA is one of the few enzymes in the outer membrane of these bacteria. This 31 kDa protein hydrolyses phospholipids, displays broad substrate specificity, is strictly calcium dependent and shows no sequence homology with water soluble (phospho)lipases or with the structurally related porins. This phospholipase is surrounded by its own substrate but is dormant in normally growing cells. Perturbations of the membrane trigger the hydrolysis of phospholipids by forming active dimers.
We report the crystal structure of this
membrane enzyme to 2.4 A resolution. The fold is similar to the
unrelated porins, revealing a 12 stranded anti-parallel
ß-barrel. The active site is located at the end of a ß-strand
and it harbours a unique catalytic triad comprising an
asparagine, histidine and a serine. Furthermore, the calcium
binding site has been identified as well as the dimerisation
interface.