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HIV-1 Capsid

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When human immundeficiency virus (HIV) infects a human cell, it releases into the interior of the cell its capsid (made of about 1,300 identical so-called CA proteins), a closed, stable container that protects the viral genetic material (see also June 2013 highlight Elusive HIV-1 Capsid and August 2015 highlight Anatomy of a Dormant Killer). Once in the cell ― while avoiding detection by cellular proteins ― the capsid deceives the cell and directs the cell machinery to transport it to the nucleus. The human-cell protein Cyclophilin A (CypA) is thereby exploited to act against the cell's well being and to assist the HIV infection by getting the capsid to access the cell nucleus; this results in a delicate choreography accomplished by escaping anti-viral proteins in the cell and deceiving transport proteins at the nucleus, all of which contain a CypA domain that interacts directly with the capsid. Despite the availability of the crystal structure of the complex of CypA and CA proteins determined nearly 20 years ago, the mechanism by which CypA assists the capsid has been unclear due to the lack of information on CypA in complex with not one CA protein, but the entire capsid. In collaboration with experimental groups, computational biologist have shown in a recent report that the effects of CypA on the capsid are not only structural, but also dynamical. Thus, new therapeutic strategies may be envisioned through modulation of the dynamics of the capsid by small-molecule (drug) compounds that inhibit the binding of CypA to the capsid. More information is available on our retrovirus website and in a YouTube video.