HIV Gag: the intriguing complexity of host-pathogen interactions

Proteome analysis of the HIV-1 Gag interactome

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Isn’t it fascinating how a virus can hijack a number of cellular pathways for its replication – with a limited number of viral proteins? Although HIV is relatively well-studied, many aspects of its replication cycle remain poorly understood. A more thorough characterization of virus-host interactions will not only increase biological insight, but may lead to the development of new therapeutic options for HIV/AIDS patients. This motivated us to screen for cellular proteins which interact with the HIV structural protein Gag.

In order to identify proteins which interact with HIV Gag, we chose an affinity purification/mass spectrometry approach. The challenge was to discriminate specifically co-purifying proteins from screening artifacts. Many abundant and ‘sticky’ proteins tend to co-purify non-specifically in affinity purification experiments. We reasoned that proteins identified by different affinity purification (AP) methods would less likely be false positive hits. Therefore, we performed screens with three AP methods:  tandem affinity purification, magnetic beads and GFP nanotrap. In one screen, we used a metabolic labeling approach (SILAC) to obtain quantitative mass spectrometry data. Also, we developed scoring criteria and artifact filters to identify the most promising interaction candidates.

The cellular protein Lyric was identified in all screens, not excluded by the artifact filters and achieved a high SILAC score and was previously chosen for further characterization (Engeland et al., 2011). However, rather than binding only individual proteins, we assume that Gag interacts with molecular complexes within the cell to achieve assembly of virions. We found that many of the highest scoring interaction candidates belong to distinct biological pathways, such as RNA interference, the tRNA synthetase complex or the host antiviral response. Protein classes overrepresented in the interaction data included helicases, chaperones, cytoskeleton and motor proteins. A cluster containing centrosomal, gamma tubulins and kinesins as well as a cluster of serine-/arginine-rich proteins co-purified with Gag. Ribonucleoprotein complexes were by far the most enriched in our dataset, suggesting that HIV Gag may co-opt cellular RNA transport complexes to direct viral RNA to the site of assembly.

A number of promising HIV Gag binding candidates from our screens await further investigation. Taken together, our work now published in Virology highlights the intriguing complexity of host-pathogen interactions.

The left panel of the Figure shows the HIV structural protein Gag inside a cell, the right panel shows RNP complex proteins which co-purified with Gag.
The left panel of the Figure shows the HIV structural protein Gag inside a cell, the right panel shows RNP complex proteins which co-purified with Gag.

Introducing the author

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Christine Engeland, lead author of the study
Department of Infectious Diseases, Virology, Universitätsklinikum Heidelberg, Germany.

About the research

Proteome analysis of the HIV-1 Gag interactome
Virology, Volumes 460–461, July 2014, Pages 194–206
Christine E. Engeland, Nigel P. Brown, Kathleen Börner, Michael Schümann, Eberhard Krause, Lars Kaderali, Gerd A. Müller, Hans-Georg Kräusslich

Read the full article on ScienceDirect.

Additional reference:
The cellular protein lyric interacts with HIV-1 Gag.
Engeland CE, Oberwinkler H, Schümann M, Krause E, Müller GA, Kräusslich HG.
J Virol. 2011 Dec;85(24):13322-32. doi: 10.1128/JVI.00174-11.

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