Salvi, N. | Search bioRxiv

bioRxiv2022

Structural insights into the regulation of acetylation-dependent genome condensation

Histone modifications are deposited by chromatin modifying enzymes and read out by proteins that recognize the modified state. BRD4-NUT is an oncogenic fusion protein of the acetyl lysine reader BRD4 that binds to the acetylase p300 and enables formation of long-range intra- and interchromosomal interactions. We here examine how acetylation reading and writing enable formation of such interactions. We show that NUT contains an acidic transcriptional activation domain that binds to the TAZ2 domain of p300. We use NMR to investigate the structure of the complex and found that the TAZ2 domain has an autoinhibitory role for p300. NUT-TAZ2 interaction or mutations found in cancer that interfere with autoinhibition by TAZ2 allosterically activate p300. p300 activation results in a self-organizing, acetylation-dependent feed-forward reaction that enables long-range interactions by bromodomain multivalent acetyl-lysine binding. We discuss the implications for chromatin organisation, gene regulation and dysregulation in disease.

biochemistry↗

bioRxiv2020

Molecular Basis of Host-Adaptation Interactions between Influenza Virus Polymerase PB2 Subunit and ANP32A

Avian influenza polymerase undergoes host adaptation in order to efficiently replicate in human cells. Adaptive mutants are localised on the C-terminal (627-NLS) domains of the PB2 subunit. In particular mutation of PB2 residue 627 from E to K in avian polymerase rescues activity in mammalian cells. A host transcription regulator ANP32A, comprising a long C-terminal intrinsically disordered domain (IDD), has also been shown to be responsible for this viral adaptation. Human ANP32A IDD lacks a 33 residue insertion compared to avian ANP32A, a deletion that restricts avian influenza polymerase activity in mammalian cells. We determined conformational descriptions of the highly dynamic complexes between 627E and 627K forms of the 627-NLS domains of PB2 and avian and human ANP32A. The negatively charged intrinsically disordered domain of human ANP32A transiently binds to a basic face of the 627 domain, exploiting multiple binding sites to maximize affinity for 627-NLS. This interaction also implicates residues 590 and 591 that are responsible for human-adaptation of the the 2009 pandemic influenza polymerase. The presence of 627E interrupts the polyvalency of the interaction, an effect that is compensated by extending the interaction surface and exploiting an avian-unique motif in the unfolded domain that interacts with the 627-NLS linker. In both cases the interaction favours the open, dislocated form of the 627-NLS domains. Importantly the two binding modes exploited by human- and avian-adapted PB2 are strongly abrogated in the cross interaction between avian polymerase and human ANP32A, suggesting that this molecular specificity may be related to species adaptation. The observed binding mode is maintained in the context of heterotrimeric influenza polymerase, placing ANP32A in the immediate vicinity of known host-adaptive PB2 mutants. This study provides a molecular framework for understanding the species-specific restriction of influenza polymerase by ANP32A and will inform the identification of new targets for influenza inhibition.

biophysics↗