CRYO-EM STRUCTURE OF THE DELTA-RETROVIRAL INTASOME IN COMPLEX WITH THE PP2A REGULATORY SUBUNIT B56γ

Abstract

2The Retroviridae delta-retrovirus genus includes the most oncogenic pathogen -human T-cell lymphotropic virus type 1 (HTLV-1)(1). Many of the ~20 million people infected with HTLV-1 will develop severe leukaemia (2) or an ALS-like motor disease (3) unless a therapy becomes available. A key step in the establishment of infection is the integration of viral genetic material into the host genome, catalysed by the viral integrase (IN) enzyme. Here we used X-ray crystallography and single-particle cryo-electron microscopy to determine the structure of functional delta-retroviral IN assembled on viral DNA ends and bound the B56g subunit of its human host factor, the protein phosphatase 2A (4). The structure reveals a tetrameric IN assembly bound to the phosphatase via a conserved short linear motif found within the extended linker connecting the catalytic core (CCD) and C-terminal (CTD) IN domains. Unexpectedly, all four IN subunits are involved in B56g binding, taking advantage of the flexibility of the CCD-CTD linkers. Our results fill the current gap in the structural understanding of the delta-retroviral integration machinery. Insight into the interactions between the delta-retroviral intasome and the host will be crucial for understanding the pattern of integration events in infected individuals and therefore bears important clinical implications.

Mechanisms of HIV-1 Integrase Resistance to Dolutegravir and Potent Inhibition of Drug Resistant Variants

“…Each step of DNA integration, up to formation of the integration intermediate, occurs within a series of stable nucleoprotein complexes (intasomes), involving a multimer of IN and a pair of viral DNA ends. The atomic structures have now been determined for a variety of retroviral intasomes (4)(5)(6)(7)(8)(9)(10)(11)(12)(13), including HIV-1 (14,15), revealing differences in the oligomeric assemblies and how they engage target DNA. The formation of intasome species, and the intasome-mediated insertion of the vDNA into the host genome, are essential steps in the viral replication cycle [see (1,2) among the best therapeutic options for use in combination therapies to treat HIV-infected patients (18).…”