PDBsum entry 2b03

Hydrolase

PDB id: 2b03

Contents

Protein chain

124 a.a.

Ligands

TUD

Metals

_CA

Waters ×69

References listed in PDB file

Key reference

Title

Structural basis for bile salt inhibition of pancreatic phospholipase a2.

Authors

Y.H.Pan, B.J.Bahnson.

Ref.

J Mol Biol, 2007, 369, 439-450. [DOI no: 10.1016/j.jmb.2007.03.034]

PubMed id

17434532

Abstract

Bile salt interactions with phospholipid monolayers of fat emulsions are known to regulate the actions of gastrointestinal lipolytic enzymes in order to control the uptake of dietary fat. Specifically, on the lipid/aqueous interface of fat emulsions, the anionic portions of amphipathic bile salts have been thought to interact with and activate the enzyme group-IB phospholipase A2 (PLA2) derived from the pancreas. To explore this regulatory process, we have determined the crystal structures of the complexes of pancreatic PLA2 with the naturally occurring bile salts: cholate, glycocholate, taurocholate, glycochenodeoxycholate, and taurochenodeoxycholate. The five PLA2-bile salt complexes each result in a partly occluded active site, and the resulting ligand binding displays specific hydrogen bonding interactions and extensive hydrophobic packing. The amphipathic bile salts are bound to PLA2 with their polar hydroxyl and sulfate/carboxy groups oriented away from the enzyme's hydrophobic core. The impaired catalytic and interface binding functions implied by these structures provide a basis for the previous numerous observations of a biphasic dependence of the rate of PLA2 catalyzed hydrolysis of zwitterionic glycerophospholipids in the presence of bile salts. The rising or activation phase is consistent with enhanced binding and activation of the bound PLA2 by the bile salt induced anionic charge in a zwitterionic interface. The falling or inhibitory phase can be explained by the formation of a catalytically inert stoichiometric complex between PLA2 and any bile salts in which it forms a stable complex. The model provides new insight into the regulatory role that specific PLA2-bile salt interactions are likely to play in fat metabolism.

Figure 3.
Figure 3. The 2.2 Å crystal structure of pancreatic group-IB PLA2 complexed with TCDC. The active site residues H48, D49 and the active site calcium (yellow) are adjacent to the bile salt bind pocket. The ligand TCDC is displayed in a space filling view with atoms colored according to the CPK convention. Apparently, the TCDC bound to the i-face partly blocks the access route to the active site. The residues K116, N23, and R6 are shown hydrogen bonded to the taurine-sulfate, 7-hydroxyl, and 3-hydroxyl groups, respectively. Hydrophobic contacts are shown with F5, I9, F22 and F106. (a) The PLA2–TCDC complex is displayed with the i-face of the protein facing the viewer. (b) The i-face of PLA2 is rotated 90° relative to the view displayed in (a) so that it now faces down. The space-filling view of TCDC shows the polar hydroxyl and sulfate groups (red oxygen atoms) facing downward as well. These views were rendered using the programs MOLSCRIPT,^29 POVSCRIPT^30 and POVRAY [www.povray.org].

Figure 7.
Figure 7. Superposition of PLA2s in complex with TCDC with structures of active site inhibitors MJ33 and MG14. (a) Overlay of PLA2–TCDC (orange) and PLA2–MJ33^17 (grey; PDB code 1fxf) structures. (b) Close-up view of (a). (c) Overlay of PLA2–TCDC (orange) and PLA2–MG14^18 (green; PDB code 1mkv) structures. (d) Close-up view of (c). These views were rendered using the programs MOLSCRIPT,^29 POVSCRIPT^30 and POVRAY [www.povray.org].

The above figures are reprinted by permission from Elsevier: J Mol Biol (2007, 369, 439-450) copyright 2007.