N-terminal half of transportin SR2 interacts with HIV integrase

Abstract

The karyopherin transportin SR2 (TRN-SR2, TNPO3) is responsible for shuttling specific cargoes such as serine/arginine-rich splicing factors from the cytoplasm to the nucleus. This protein plays a key role in HIV infection by facilitating the nuclear import of the pre-integration complex (PIC) that contains the viral DNA as well as several cellular and HIV proteins, including the integrase. The process of nuclear import is considered to be the bottleneck of the viral replication cycle and therefore represents a promising target for anti-HIV drug design. Previous studies have demonstrated that the direct interaction between TRN-SR2 and HIV integrase predominantly involves the catalytic core domain (CCD) and the C-terminal domain (CTD) of the integrase. We aimed at providing a detailed molecular view of this interaction through a biochemical characterization of the respective protein complex. Size-exclusion chromatography was used to characterize the interaction of TRN-SR2 with a truncated variant of the HIV-1 integrase, including both the CCD and CTD. These experiments indicate that one TRN-SR2 molecule can specifically bind one CCD-CTD dimer. Next, the regions of the solenoid-like TRN-SR2 molecule that are involved in the interaction with integrase were identified using AlphaScreen binding assays, revealing that the integrase interacts with the N-terminal half of TRN-SR2 principally through the HEAT repeats 4, 10, and 11. Combining these results with small-angle X-ray scattering data for the complex of TRN-SR2 with truncated integrase, we propose a molecular model of the complex. We speculate that nuclear import of the PIC may proceed concurrently with the normal nuclear transport.

The mutation of Transportin 3 gene that causes limb girdle muscular dystrophy 1F induces protection against HIV-1 infection

“…However the exact mechanism of action of TNPO3 still remains a matter of controversy [38]. Some studies suggest that TNPO3 participates in the nuclear import of PICs [9,25,39,40] whereas other authors propose that TNPO3 promotes HIV-1 infection though the interaction with HIV-1 CA [41–43] or indirectly through the interaction of CPSF6 with HIV-1 CA [12]. Besides an indirect role for TNPO3 in viral integration through its interaction with CA and/or the IN and their respective cellular partners such as CPSF6 or LEDGF/p75 [38] has been proposed.…”

“…Several cellular import factors, including importin-7, importin-α3 and Transportin 3 (TNPO3, also called TRN-SR2) have also been involved in HIV-1 nuclear import [8]. Apart from its implication in nuclear import of the viral PIC, it has been confirmed that N-terminal end of TNPO3 protein act as a direct binding partner of HIV-1 IN [9]. Interaction with the viral CA has also been documented [10,11] and nearly 30 CA-mutants able to modify HIV-1 dependence on TNPO3 have been described [12].…”

The role of integration and clonal expansion in HIV infection: live long and prosper

“…Cellular proteins interacting with the PIC include the barrier to autointegration factor 1 (BAF1), high mobility group proteins (HMG), lamina-associated polypeptide 2α (LAP2α), lens-epithelium-derived growth factor (LEDGF/p75), and the karyopherin transportin SR2 (TRN-SR2, TNPO3). TNPO3 binds directly to the CCD and CTD of IN [ 149 ] and may participate in shuttling the PIC to the nucleus. The size of the PIC is uncertain, but it must fit through the nuclear pore, and the process of import is essential yet remains unclear.…”

TNPO3-mediated nuclear entry of the Rous sarcoma virus Gag protein is independent of the cargo-binding domain

“…Taken together, these results suggest that the major points of contact are the Gag MA region and the TNPO3 NPC binding domain, although it is important to note that other regions of Gag and TNPO3 appear to be required for maximal binding to occur. A recent study demonstrated that the N-terminus of TNPO3 (containing the RanGTP binding domain and part of the NPC interaction domain) interacts with the catalytic core domain and C-terminal domain of HIV-1 integrase, suggesting that other retroviral cargoes of TNPO3 bind to sites outside of the CBD (49).…”