Catechol estrogens are steroid metabolites that elicit physiological responses through binding to a variety of cellular targets. We show here that catechol estrogens directly inhibit soluble adenylyl cyclases and the abundant trans-membrane adenylyl cyclases. Catechol estrogen inhibition is non-competitive with respect to the substrate ATP, and we solved the crystal structure of a catechol estrogen bound to a soluble adenylyl cyclase from Spirulina platensis in complex with a substrate analog. The catechol estrogen is bound to a newly identified, conserved hydrophobic patch near the active center but distinct from the ATP-binding cleft. Inhibitor binding leads to a chelating interaction between the catechol estrogen hydroxyl groups and the catalytic magnesium ion, distorting the active site and trapping the enzyme substrate complex in a non-productive conformation. This novel inhibition mechanism likely applies to other adenylyl cyclase inhibitors, and the identified ligand-binding site has important implications for the development of specific adenylyl cyclase inhibitors.
In comparison with the ␣ subunit of G proteins, the role of the  subunit in signaling is less well understood. During the regulation of effectors by the ␥ complex, it is known that the  subunit contacts effectors directly, whereas the role of the  subunit is undefined in receptor-G protein interaction. Among the five G protein  subunits known, the  4 subunit type is the least studied. We compared the ability of ␥ complexes containing  4 and the well characterized  1 to stimulate three different effectors: phospholipase C-2, phospholipase C-3, and adenylyl cyclase type II.  4 ␥ 2 and  1 ␥ 2 activated all three of these effectors with equal efficacy. However, nucleotide exchange in a G protein constituting ␣ o  4 ␥ 2 was stimulated significantly more by the M2 muscarinic receptor compared with ␣ o  1 ␥ 2 . Because ␣ o forms heterotrimers with  4 ␥ 2 and  1 ␥ 2 equally well, these results show that the  subunit type plays a direct role in the receptor activation of a G protein.The G protein ␥ complex regulates the activity of a diverse set of effectors, including phospholipases, adenylyl cyclases, and ion channels (1). There is evidence that the  subunit in the complex interacts directly with effectors (2-5). There are five  subtypes ( 1 - 5 ) as well as an alternatively spliced version of  5 (known as  5 -long) (6 -11).  1 - 4 share over 80% identity with one another, whereas  5 shares only ϳ50% identity with the other  subunits (12). The divergence between  5 and the other  subunits is consistent with the functional differences between  5 and  1 observed in effector regulation in a variety of systems (4,13,14). The high sequence similarity of  1 - 4 suggests that their functions are conserved. Although some experiments indicated little difference in effector modulating capability among these  subunit types, other experiments suggest otherwise. The G protein-coupled receptor kinase GRK3 binds ␥ complexes consisting of  1 ,  2 , and  3 , but only  1 and  2 bind to the related kinase GRK2 (15). Other results indicate the selective mediation of cross-talk between G proteins and protein kinase C modulation of N-type channels by the  1 subunit type (16).Experiments focusing on the specific role of individual G protein subunit types have provided evidence for a certain level of selectivity in the interaction of ␣ subunit types with receptors (17). Evidence for similar selectivity of interaction between ␥ subunit types and receptors also exists (18 -20). In contrast there is limited evidence for  subunit type selectivity in receptor interaction. Whole-cell experiments using antisense oligonucleotides directed against specific  subunit cDNAs selectively disrupted signaling from particular receptors (21). Although the selective interaction of  subunit types with receptors could give rise to this result, such selectivity has not been shown so far.Among the five  subunits,  4 is the least studied. Its role in effector regulation and receptor interaction remains unclear. To exam...
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.