Systematic identification and characterization of genes in the regulation and biogenesis of photosynthetic machinery.

Photosynthesis is central to food production and the Earth's biogeochemistry, yet the molecular basis for its regulation remains poorly understood. Here, using high-throughput genetics in the model eukaryotic alga Chlamydomonas reinhardtii, we identify with high confidence (false discovery rate [FDR] < 0.11) 70 poorly characterized genes required for photosynthesis. We then enable the functional characterization of these genes by providing a resource of proteomes of mutant strains, each lacking one of these genes. The data allow assignment of 34 genes to the biogenesis or regulation of one or more specific photosynthetic complexes. Further analysis uncovers biogenesis/regulatory roles for at least seven proteins, including five photosystem I mRNA maturation factors, the chloroplast translation factor MTF1, and the master regulator PMR1, which regulates chloroplast genes via nuclear-expressed factors. Our work provides a rich resource identifying regulatory and functional genes and placing them into pathways, thereby opening the door to a system-level understanding of photosynthesis.

STING Polymer Structure Reveals Mechanisms for Activation, Hyperactivation, and Inhibition.

How the central innate immune protein, STING, is activated by its ligands remains unknown. Here, using structural biology and biochemistry, we report that the metazoan second messenger 2'3'-cGAMP induces closing of the human STING homodimer and release of the STING C-terminal tail, which exposes a polymerization interface on the STING dimer and leads to the formation of disulfide-linked polymers via cysteine residue 148. Disease-causing hyperactive STING mutations either flank C148 and depend on disulfide formation or reside in the C-terminal tail binding site and cause constitutive C-terminal tail release and polymerization. Finally, bacterial cyclic-di-GMP induces an alternative active STING conformation, activates STING in a cooperative manner, and acts as a partial antagonist of 2'3'-cGAMP signaling. Our insights explain the tight control of STING signaling given varying background activation signals and provide a therapeutic hypothesis for autoimmune syndrome treatment.

Structural Insights into STING Signaling.

Since its discovery 12 years ago, the stimulator of interferon genes (STING) pathway has attracted the intense focus of top cell biologists, biochemists, and structural biologists, due to its unique activation mechanisms and broad implications in cancer, aging, and autoimmunity. The STING pathway is an essential innate immune signaling cascade responsible for the sensing of aberrant cytosolic double-stranded DNA (dsDNA), which is a hallmark of cancer and viral infection. Erroneous STING activation can exacerbate many autoimmune and inflammatory syndromes. Therefore, it is remarkable how rapidly, effectively, and specifically the STING pathway responds to a myriad of threats while generally maintaining immune homeostasis. Here we review high-impact structural work that collectively paints a picture of STING signaling with atomic resolution. The elegant molecular mechanisms not only give clues to how STING has evolved to distinguish between self and foreign, but they also enable development of novel therapeutics to treat STING-related diseases.