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General Model for Retroviral Capsid Pattern Recognition by TRIM5 Proteins.

ABSTRACT: Restriction factors are intrinsic cellular defense proteins that have evolved to block microbial infections. Retroviruses such as HIV-1 are restricted by TRIM5 proteins, which recognize the viral capsid shell that surrounds, organizes, and protects the viral genome. TRIM5? uses a SPRY domain to bind capsids with low intrinsic affinity (KD of >1 mM) and therefore requires higher-order assembly into a hexagonal lattice to generate sufficient avidity for productive capsid recognition. TRIMCyp, on the other hand, binds HIV-1 capsids through a cyclophilin A domain, which has a well-defined binding site and higher affinity (KD of ?10 ?M) for isolated capsid subunits. Therefore, it has been argued that TRIMCyp proteins have dispensed with the need for higher-order assembly to function as antiviral factors. Here, we show that, consistent with its high degree of sequence similarity with TRIM5?, the TRIMCyp B-box 2 domain shares the same ability to self-associate and facilitate assembly of a TRIMCyp hexagonal lattice that can wrap about the HIV-1 capsid. We also show that under stringent experimental conditions, TRIMCyp-mediated restriction of HIV-1 is indeed dependent on higher-order assembly. Both forms of TRIM5 therefore use the same mechanism of avidity-driven capsid pattern recognition.IMPORTANCE Rhesus macaques and owl monkeys are highly resistant to HIV-1 infection due to the activity of TRIM5 restriction factors. The rhesus macaque TRIM5? protein blocks HIV-1 through a mechanism that requires self-assembly of a hexagonal TRIM5? lattice around the invading viral core. Lattice assembly amplifies very weak interactions between the TRIM5? SPRY domain and the HIV-1 capsid. Assembly also promotes dimerization of the TRIM5? RING E3 ligase domain, resulting in synthesis of polyubiquitin chains that mediate downstream steps of restriction. In contrast to rhesus TRIM5?, the owl monkey TRIM5 homolog, TRIMCyp, binds isolated HIV-1 CA subunits much more tightly through its cyclophilin A domain and therefore was thought to act independently of higher-order assembly. Here, we show that TRIMCyp shares the assembly properties of TRIM5? and that both forms of TRIM5 use the same mechanism of hexagonal lattice formation to promote viral recognition and restriction.

SUBMITTER: Wagner JM

PROVIDER: S-EPMC5790955 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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General Model for Retroviral Capsid Pattern Recognition by TRIM5 Proteins.

Wagner Jonathan M JM Christensen Devin E DE Bhattacharya Akash A Dawidziak Daria M DM Roganowicz Marcin D MD Wan Yueping Y Pumroy Ruth A RA Demeler Borries B Ivanov Dmitri N DN Ganser-Pornillos Barbie K BK Sundquist Wesley I WI Pornillos Owen O

Journal of virology 20180130 4

Restriction factors are intrinsic cellular defense proteins that have evolved to block microbial infections. Retroviruses such as HIV-1 are restricted by TRIM5 proteins, which recognize the viral capsid shell that surrounds, organizes, and protects the viral genome. TRIM5α uses a SPRY domain to bind capsids with low intrinsic affinity (<i>K<sub>D</sub></i> of >1 mM) and therefore requires higher-order assembly into a hexagonal lattice to generate sufficient avidity for productive capsid recognit ...[more]

PMID: 29187540

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Project description:TRIM5 proteins can restrict retroviral infection soon after delivery of the viral core into the cytoplasm. However, the molecular mechanisms by which TRIM5? inhibits infection have been elusive, in part due to the difficulty of developing and executing biochemical assays that examine this stage of the retroviral life cycle. Prevailing models suggest that TRIM5? causes premature disassembly of retroviral capsids and/or degradation of capsids by proteasomes, but whether one of these events leads to the other is unclear. Furthermore, how TRIM5? affects the essential components of the viral core, other than capsid, is unknown. To address these questions, we devised a biochemical assay in which the fate of multiple components of retroviral cores during infection can be determined. We utilized cells that can be efficiently infected by VSV-G-pseudotyped retroviruses, and fractionated the cytosolic proteins on linear gradients following synchronized infection. The fates of capsid and integrase proteins, as well as viral genomic RNA and reverse transcription products were then monitored. We found that components of MLV and HIV-1 cores formed a large complex under non-restrictive conditions. In contrast, when MLV infection was restricted by human TRIM5?, the integrase protein and reverse transcription products were lost from infected cells, while capsid and viral RNA were both solubilized. Similarly, when HIV-1 infection was restricted by rhesus TRIM5? or owl monkey TRIMCyp, the integrase protein and reverse transcription products were lost. However, viral RNA was also lost, and high levels of preexisting soluble CA prevented the determination of whether CA was solubilized. Notably, proteasome inhibition blocked all of the aforementioned biochemical consequences of TRIM5?-mediated restriction but had no effect on its antiviral potency. Together, our results show how TRIM5? affects various retroviral core components and indicate that proteasomes are required for TRIM5?-induced core disruption but not for TRIM5?-induced restriction.

Dataset Information

General Model for Retroviral Capsid Pattern Recognition by TRIM5 Proteins.

Publications

General Model for Retroviral Capsid Pattern Recognition by TRIM5 Proteins.

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