Download MendeleyFatty Acid Binding to the Allosteric Subunit of Cyclooxygenase-2 Relieves a Tonic Inhibition of the Catalytic Subunit.
Dong, L., Yuan, C., Orlando, B.J., Malkowski, M.G., Smith, W.L.(2016) J Biol Chem 291: 25641-25655
- PubMed: 27756840
- DOI: https://doi.org/10.1074/jbc.M116.757310
- Primary Citation of Related Structures:
5JVY, 5JVZ, 5JW1 - PubMed Abstract:
Prostaglandin endoperoxide H synthase-2 (PGHS-2), also called cyclooxygenase-2 (COX-2), converts arachidonic acid to PGH 2 PGHS-2 is a conformational heterodimer composed of allosteric (E allo ) and catalytic (E cat ) subunits. Fatty acids (FAs) bind to Arg-120 of E allo increasing to different degrees, depending on the FA, the V max of its E cat partner. We report here that movement of helical residues 120-122 and loop residues 123-129 of E allo underlies the allosteric effects of FAs and allosteric COX-2 inhibitors, including naproxen and flurbiprofen. An S121P substitution in both PGHS-2 monomers yields a variant (S121P/S121P PGHS-2) that has 1.7-1.8 times the V max of native PGHS-2 and is relatively insensitive to activation by FAs or inhibition by allosteric inhibitors. The S121P substitution in E allo is primarily responsible for these effects. In X-ray crystal structures, the C¦Á atoms of helical residues 119-122 of S121P/S121P PGHS-2 are displaced from their normal positions. Additionally, the S121P/S121P PGHS-2 variants in which Pro-127 and Ser-541 are replaced by cysteines spontaneously forms Cys-127 to Cys-541 cross-links between monomers. This is unlike the corresponding native PGHS-2 variant and suggests that S121P substitutions also unhinge the loop involving residues 123-129. We conclude the following: (a) the region involving residues 120-129 of unoccupied E allo tonically inhibits E cat ; (b) binding of an activating FA (e.g. arachidonic, palmitic, or oleic acid) to E allo or an S121P substitution in E allo repositions this region to increase E cat activity; and (c) allosteric COX inhibitors act by preventing FA binding to E allo and additionally by relocating E allo residues to inhibit E cat .
Organizational Affiliation:
From the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109 and.
