Implementing fluorescence anisotropy screening and crystallographic analysis to define PKA isoform-selective activation by cAMP analogs

Gαs-Protein Kinase A (PKA) Pathway Signalopathies: The Emerging Genetic Landscape and Therapeutic Potential of Human Diseases Driven by Aberrant Gαs-PKA Signaling

Many of the fundamental concepts of signal transduction and kinase activity are attributed to the discovery and crystallization of cAMP-dependent protein kinase, or protein kinase A. PKA is one of the best-studied kinases in human biology, with emphasis in biochemistry and biophysics, all the way to metabolism, hormone action, and gene expression regulation. It is surprising, however, that our understanding of PKA's role in disease is largely underappreciated. Although genetic mutations in the PKA holoenzyme are known to cause diseases such as Carney complex, Cushing syndrome, and acrodysostosis, the story largely stops there. With the recent explosion of genomic medicine, we can finally appreciate the broader role of the Gαs-PKA pathway in disease, with contributions from aberrant functioning G proteins and G protein-coupled receptors, as well as multiple alterations in other pathway components and negative regulators. Together, these represent a broad family of diseases we term the Gαs-PKA pathway signalopathies. The Gαs-PKA pathway signalopathies encompass diseases caused by germline, postzygotic, and somatic mutations in the Gαs-PKA pathway, with largely endocrine and neoplastic phenotypes. Here, we present a signaling-centric review of Gαs-PKA-driven pathophysiology and integrate computational and structural analysis to identify mutational themes commonly exploited by the Gαs-PKA pathway signalopathies. Major mutational themes include hotspot activating mutations in Gαs, encoded by GNAS, and mutations that destabilize the PKA holoenzyme. With this review, we hope to incite further study and ultimately the development of new therapeutic strategies in the treatment of a wide range of human diseases. SIGNIFICANCE STATEMENT: Little recognition is given to the causative role of Gαs-PKA pathway dysregulation in disease, with effects ranging from infectious disease, endocrine syndromes, and many cancers, yet these disparate diseases can all be understood by common genetic themes and biochemical signaling connections. By highlighting these common pathogenic mechanisms and bridging multiple disciplines, important progress can be made toward therapeutic advances in treating Gαs-PKA pathway-driven disease.

Disrupting the Allosteric Interaction between the Plasmodium falciparum cAMP-dependent Kinase and Its Regulatory Subunit

The ubiquitous second messenger cAMP mediates signal transduction processes in the malarial parasite that regulate host erythrocyte invasion and the proliferation of merozoites. In Plasmodium falciparum, the central receptor for cAMP is the single regulatory subunit (R) of protein kinase A (PKA). To aid the development of compounds that can selectively dysregulate parasite PKA signaling, we solved the structure of the PKA regulatory subunit in complex with cAMP and a related analogue that displays antimalarial activity, (S_p)-2-Cl-cAMPS. Prior to signaling, PKA-R holds the kinase's catalytic subunit (C) in an inactive state by exerting an allosteric inhibitory effect. When two cAMP molecules bind to PKA-R, they stabilize a structural conformation that facilitates its dissociation, freeing PKA-C to phosphorylate downstream substrates such as apical membrane antigen 1. Although PKA activity was known to be necessary for erythrocytic proliferation, we show that uncontrolled induction of PKA activity using membrane-permeable agonists is equally disruptive to growth.

A tool set to map allosteric networks through the NMR chemical shift covariance analysis

Allostery is an essential regulatory mechanism of biological function. Allosteric sites are also pharmacologically relevant as they are often targeted with higher selectivity than orthosteric sites. However, a comprehensive map of allosteric sites poses experimental challenges because allostery is driven not only by structural changes, but also by modulations in dynamics that typically remain elusive to classical structure determination methods. An avenue to overcome these challenges is provided by the NMR chemical shift covariance analysis (CHESCA), as chemical shifts are exquisitely sensitive to redistributions in dynamic conformational ensembles. Here, we propose a set of complementary CHESCA algorithms designed to reliably detect allosteric networks with minimal occurrences of false positives or negatives. The proposed CHESCA toolset was tested for two allosteric proteins (PKA and EPAC) and is expected to complement traditional comparative structural analyses in the comprehensive identification of functionally relevant allosteric sites, including those in otherwise elusive partially unstructured regions.

Considering effects of nanosecond pulsed electric fields on proteins

Most, if not all, effects of intense, pulsed electric fields are analyzed in terms of electrical charging of plasma membranes and/or subcellular membranes. However, not all cell responses from nanosecond pulsed electric fields (nsPEFs) are fully explained by poration of cell membranes. Observations that nsPEFs induce a Ca2-dependent dissipation of the mitochondria membrane potential (ΔΨm), which is enhanced when high frequency components are present in fast rise-fall waveforms, are not compatible with a poration event. Ca(2+) is shown to have little or no effect on propidium iodide uptake as a measure of plasma membrane poration and consequently intracellular membranes. Since most if not all Ca(2+)-regulated events are mediated by proteins, actions of nsPEFs on a protein(s) that regulate and/or affect the mitochondria membrane potential are possible. To show that nsPEFs can directly affect proteins, nsPEFs non-thermally inactivated the catalytic (phosphotransferase) activity of the catalytic subunit of the cAMP-dependent protein kinase, which is the prototype of the protein kinase superfamily that share a common catalytic mechanism and whose functions are highly dependent on their structure. These studies present indirect and direct evidences that nsPEFs can affect proteins and their functions, at least in part, by affecting their structure.