Hexasome-INO80 complex reveals structural basis of noncanonical nucleosome remodeling.

Loss of H2A-H2B histone dimers is a hallmark of actively transcribed genes, but how the cellular machinery functions in the context of noncanonical nucleosomal particles remains largely elusive. In this work, we report the structural mechanism for adenosine 5'-triphosphate-dependent chromatin remodeling of hexasomes by the INO80 complex. We show how INO80 recognizes noncanonical DNA and histone features of hexasomes that emerge from the loss of H2A-H2B.

Structural mechanism of extranucleosomal DNA readout by the INO80 complex.

The nucleosomal landscape of chromatin depends on the concerted action of chromatin remodelers. The INO80 remodeler specifically places nucleosomes at the boundary of gene regulatory elements, which is proposed to be the result of an ATP-dependent nucleosome sliding activity that is regulated by extranucleosomal DNA features. Here, we use cryo-electron microscopy and functional assays to reveal how INO80 binds and is regulated by extranucleosomal DNA.

Genome information processing by the INO80 chromatin remodeler positions nucleosomes.

The fundamental molecular determinants by which ATP-dependent chromatin remodelers organize nucleosomes across eukaryotic genomes remain largely elusive. Here, chromatin reconstitutions on physiological, whole-genome templates reveal how remodelers read and translate genomic information into nucleosome positions. Using the yeast genome and the multi-subunit INO80 remodeler as a paradigm, we identify DNA shape/mechanics encoded signature motifs as sufficient for nucleosome positioning and distinct from known DNA sequence preferences of histones.

Ruler elements in chromatin remodelers set nucleosome array spacing and phasing.

Arrays of regularly spaced nucleosomes dominate chromatin and are often phased by alignment to reference sites like active promoters. How the distances between nucleosomes (spacing), and between phasing sites and nucleosomes are determined remains unclear, and specifically, how ATP-dependent chromatin remodelers impact these features. Here, we used genome-wide reconstitution to probe how Saccharomyces cerevisiae ATP-dependent remodelers generate phased arrays of regularly spaced nucleosomes.

Structural basis for ATP-dependent chromatin remodelling by the INO80 complex.

In the eukaryotic nucleus, DNA is packaged in the form of nucleosomes, each of which comprises about 147 base pairs of DNA wrapped around a histone protein octamer. The position and histone composition of nucleosomes is governed by ATP-dependent chromatin remodellers such as the 15-subunit INO80 complex . INO80 regulates gene expression, DNA repair and replication by sliding nucleosomes, the exchange of histone H2A.

Single-molecule nucleosome remodeling by INO80 and effects of histone tails.

Genome maintenance and integrity requires continuous alterations of the compaction state of the chromatin structure. Chromatin remodelers, among others the INO80 complex, help organize chromatin by repositioning, reshaping, or evicting nucleosomes. We report on INO80 nucleosome remodeling, assayed by single-molecule Foerster resonance energy transfer on canonical nucleosomes as well as nucleosomes assembled from tailless histones.

ATP hydrolysis by the viral RNA sensor RIG-I prevents unintentional recognition of self-RNA.

The cytosolic antiviral innate immune sensor RIG-I distinguishes 5' tri- or diphosphate containing viral double-stranded (ds) RNA from self-RNA by an incompletely understood mechanism that involves ATP hydrolysis by RIG-I's RNA translocase domain. Recently discovered mutations in ATPase motifs can lead to the multi-system disorder Singleton-Merten Syndrome (SMS) and increased interferon levels, suggesting misregulated signaling by RIG-I. Here we report that SMS mutations phenocopy a mutation that allows ATP binding but prevents hydrolysis.

Structural mechanism of cytosolic DNA sensing by cGAS.

Cytosolic DNA arising from intracellular bacterial or viral infections is a powerful pathogen-associated molecular pattern (PAMP) that leads to innate immune host defence by the production of type I interferon and inflammatory cytokines. Recognition of cytosolic DNA by the recently discovered cyclic-GMP-AMP (cGAMP) synthase (cGAS) induces the production of cGAMP to activate the stimulator of interferon genes (STING). Here we report the crystal structure of cGAS alone and in complex with DNA, ATP and GTP along with functional studies.

Paramyxovirus V proteins disrupt the fold of the RNA sensor MDA5 to inhibit antiviral signaling.

The retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) melanoma differentiation-associated protein 5 (MDA5) senses cytoplasmic viral RNA and activates antiviral innate immunity. To reveal how paramyxoviruses counteract this response, we determined the crystal structure of the MDA5 adenosine 5'-triphosphate (ATP)-hydrolysis domain in complex with the viral inhibitor V protein. The V protein unfolded the ATP-hydrolysis domain of MDA5 via a β-hairpin motif and recognized a structural motif of MDA5 that is normally buried in the conserved helicase fold.

The RIG-I ATPase domain structure reveals insights into ATP-dependent antiviral signalling.

RIG-I detects cytosolic viral dsRNA with 5' triphosphates (5'-ppp-dsRNA), thereby initiating an antiviral innate immune response. Here we report the crystal structure of superfamily 2 (SF2) ATPase domain of RIG-I in complex with a nucleotide analogue. RIG-I SF2 comprises two RecA-like domains 1A and 2A and a helical insertion domain 2B, which together form a 'C'-shaped structure.

Structure and mechanism of the Swi2/Snf2 remodeller Mot1 in complex with its substrate TBP.

Swi2/Snf2-type ATPases regulate genome-associated processes such as transcription, replication and repair by catalysing the disruption, assembly or remodelling of nucleosomes or other protein-DNA complexes. It has been suggested that ATP-driven motor activity along DNA disrupts target protein-DNA interactions in the remodelling reaction. However, the complex and highly specific remodelling reactions are poorly understood, mostly because of a lack of high-resolution structural information about how remodellers bind to their substrate proteins.