Cyclo
pentenone
prostanoids (cyP) arise as im
portant modulators of inflammation and cell
proliferation. Although their
physiological significance has not been fully elucidated, their
potent biologicaleffects have s
purred their study as leads for the develo
pment of thera
peutic agents. A key determinant ofcyP action is their ability to bind to thiol grou
ps in
proteins or in glutathione through Michael addition.Even though several
protein targets for cyP addition have been identified, little is known about the structuraldeterminants from the
protein or the cyP that drive this modification. The results herein
presented
providethe first evidence that cyP with different structures target distinct thiol sites in a
protein molecule, namely,H-Ras. Whereas 15-deoxy-
12,14-
prostaglandin J
2 (15d-PGJ
2) and
12-PGJ
2 preferentially target theC-terminal region containing cysteines 181 and 184, PGA
1 and 8-iso-PGA
1 bind mainly to cysteine 118,located in the GTP-binding motif. The biological counter
parts of this s
pecificity are the site-selectivemodification and activation of H-Ras in cells and the differential interaction of cyP with H, N, and K-Ras
proteins. Cysteine 184 is unique to H-Ras, whereas cysteine 118 is
present in the three Ras homologues.Consistent with this, PGA
1 binds to and activates H-, N-, and K-Ras, thus differing from the
preferentialinteraction of 15d-PGJ
2 with H-Ras. These results
put forward the
possibility of influencing the selectivityof cyP-
protein addition by modifying cyP structure. Furthermore, they may o
pen new avenues for thedevelo
pment of cyP-based drugs.