Ligand Strain and Its Conformational Complexity Is a Major Factor in the Binding of Cyclic Dinucleotides to STING Protein

Abstract

STING (stimulator of interferon genes) is ak ey regulator of innate immunity that has recently been recognized as ap romising drug target. STING is activated by cyclic dinucleotides (CDNs) whiche ventually leads to expression of type Ii nterferons and other cytokines.F actors underlying the affinity of various CDN analogues are poorly understood. Herein, we correlate structural biology,isothermal calorimetry (ITC) and computational modeling to elucidate factors contributing to binding of six CDNs-three pairs of natural (ribo) and fluorinated (2'-fluororibo) 3',3'-CDNs.X -ray structural analyses of six {STING:CDN} complexes did not offer any explanation for the different affinities of the studied ligands. ITC showed entropy/enthalpyc ompensation up to 25 kcal mol À1 for this set of similar ligands.T he higher affinities of fluorinated analogues are explained with help of computational methods by smaller loss of entropyupon binding and by smaller strain (free) energy.

Acidity constants and protonation sites of cyclic dinucleotides determined by capillary electrophoresis, quantum chemical calculations, and NMR spectroscopy

“…The same applies for hydrodynamic radii. Very small differences were observed between pK a s of ionogenic groups of the CDN diphosphorothioate (9) and its difluorinated derivatives (10)(11)(12). Their limiting mobilities and hydrodynamic radii were also similar.…”

“…As such, the role of CDNs in defense against pathogens as well as sensing of tumor cells makes them important for understanding, and potentially for treatment, of a number of autoimmune diseases [3], cancers [4], and viral diseases [5,6], as well as having potential as adjuvants in vaccines [7]. Noticeably, one of the most intensively studied ligand-protein binding equilibria is the interaction of the STING (or its mutants) with various CDNs, including chemically modified nucleobases, phosphodiester linkages, or sugar units [8,9]. Of the particular interest is the 2′,3′-cyclic diadenosine diphosphorothioate (2′,3′-c-di-AMPS) compound, known also as ADURO-S100, which was evaluated in Phase I clinical study.…”

How Fragile We Are: Influence of Stimulator of Interferon Genes (STING) Variants on Pathogen Recognition and Immune Response Efficiency

“…As a matter of fact, only a few theoretical studies dealing with MD simulations of mutated STING have been reported to date. − Notably, a study of the interaction of the agonist DMXAA on mouse STING and cyclic dinucleotide (CDN) screening studies are available in the literature. − Very recently, MD simulations were performed on a wild-type STING model complexed with different CDNs, including cGAMP . The binding was shown to induce conformational reorganization, as also suggested by dynamic network and cross-correlation analyses.…”