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. Structures of the regulatory A-module bound to DNA clarify the mechanism of linker DNA binding. The A-module is connected to the motor unit via an HSA/post-HSA lever element to chemomechanically couple the motor and linker DNA sensing. Two notable sites of curved DNA recognition by coordinated action of the four actin/actin-related proteins and the motor suggest how sliding by INO80 can be regulated by extranucleosomal DNA features. Last, the structures clarify the recruitment of YY1/Ies4 subunits and reveal deep architectural similarities between the regulatory modules of INO80 and SWI/SNF complexes.

Mechanistic understanding of human SLFN11.

Schlafen 11 (SLFN11) is an interferon-inducible antiviral restriction factor with tRNA endoribonuclease and DNA binding functions. It is recruited to stalled replication forks in response to replication stress and inhibits replication of certain viruses such as the human immunodeficiency virus 1 (HIV-1) by modulating the tRNA pool. SLFN11 has been identified as a predictive biomarker in cancer, as its expression correlates with a beneficial response to DNA damage inducing anticancer drugs. However, the mechanism and interdependence of these two functions are largely unknown. Here, we present cryo-electron microscopy (cryo-EM) structures of human SLFN11 in its dimeric apoenzyme state, bound to tRNA and in complex with single-strand DNA. Full-length SLFN11 neither hydrolyses nor binds ATP and the helicase domain appears in an autoinhibited state. Together with biochemical and structure guided mutagenesis studies, our data give detailed insights into the mechanism of endoribonuclease activity as well as suggestions on how SLFN11 may block stressed replication forks.

Structural and biochemical characterization of human Schlafen 5.

The Schlafen family belongs to the interferon-stimulated genes and its members are involved in cell cycle regulation, T cell quiescence, inhibition of viral replication, DNA-repair and tRNA processing. Here, we present the cryo-EM structure of full-length human Schlafen 5 (SLFN5) and the high-resolution crystal structure of the highly conserved N-terminal core domain. We show that the core domain does not resemble an ATPase-like fold and neither binds nor hydrolyzes ATP. SLFN5 binds tRNA as well as single- and double-stranded DNA, suggesting a potential role in transcriptional regulation. Unlike rat Slfn13 or human SLFN11, human SLFN5 did not cleave tRNA. Based on the structure, we identified two residues in proximity to the zinc finger motif that decreased DNA binding when mutated. These results indicate that Schlafen proteins have divergent enzymatic functions and provide a structural platform for future biochemical and genetic studies.

NeissLock provides an inducible protein anhydride for covalent targeting of endogenous proteins.

The Neisseria meningitidis protein FrpC contains a self-processing module (SPM) undergoing autoproteolysis via an aspartic anhydride. Herein, we establish NeissLock, using a binding protein genetically fused to SPM. Upon calcium triggering of SPM, the anhydride at the C-terminus of the binding protein allows nucleophilic attack by its target protein, ligating the complex. We establish a computational tool to search the Protein Data Bank, assessing proximity of amines to C-termini. We optimize NeissLock using the Ornithine Decarboxylase/Antizyme complex. Various sites on the target (α-amine or ε-amines) react with the anhydride, but reaction is blocked if the partner does not dock. Ligation is efficient at pH 7.0, with half-time less than 2 min. We arm Transforming Growth Factor-α with SPM, enabling specific covalent coupling to Epidermal Growth Factor Receptor at the cell-surface. NeissLock harnesses distinctive protein chemistry for high-yield covalent targeting of endogenous proteins, advancing the possibilities for molecular engineering.