Targeting of Adenylyl Cyclase for Inhibition by Peptides and Novel Small Molecule Inhibitors

BRAND, C.; MALIK, S.; SRMCKA, A.V.; CAVASOTTO, CLAUDIO N.; DESSAUER, C.W.

Houston, TX

Conferencia; 21st Keck Annual Research Conference; 2011

The nine mammalian membrane bound isoforms of adenylyl cyclase (AC) convert ATP into cyclic AMP (cAMP), an important 2nd messenger. Control of cAMP levels through AC regulation can influence various aspects of physiology. Reduced AC5 activity alone results in reduced stress on the heart, decreased pain responses, and attenuation of both morphine dependence and withdrawal behaviors. The inability to specifically inhibit or stimulate AC isoform(s) limits exploring specific physiological roles, and there is currently a lack of AC inhibitors which can be used for therapeutic benefit. Therefore, the overarching goal of these studies is the identification and characterization of novel, specific AC inhibitors.One question regarding this goal is the potential for such small molecule inhibition to have specificity between different AC isoforms. This possibility is supported based on the ability for the small peptide SIGK, which binds to the heterotrimeric G protein βγ subunit in an area required for AC regulatory interactions, to differentially disrupt AC regulation. SIGK prevented regulation of some but not all AC isoforms by Gβγ; most notably, it is able to inhibit Gβγ stimulation of AC6, but not AC5. Thus, AC inhibitors with degrees of isoform specificity can be identified.Another question is whether novel AC inhibitors can be found which bind at or near the ATP binding pocket of AC, since current inhibitors at this site lack isoform specificity, are membrane-impermeable, or are clear risks for off-target effects. Structure-based ligand docking was performed targeting the crystallized structure of the two pseudo symmetrical cytoplasmic domains (C1 and C2) which make up the catalytic core where cAMP is synthesized. This crystal structure is identical at the ATP binding site in amino acid sequence to that for human AC5, providing appropriate context for use as a docking target. The results of  docking ligands known to inhibit AC are explored in the context of eventually identifying novel, specific AC inhibitors.