Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 101, Issue 2, Pages 517-522Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0305665101
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Funding
- NCRR NIH HHS [S10-RR15899] Funding Source: Medline
- NIAID NIH HHS [R37 AI030917, AI30917] Funding Source: Medline
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The myristoylated matrix protein (myr-MA) of HIV functions as a regulator of intracellular localization, targeting the Gag precursor polyprotein to lipid rafts in the plasma membrane during virus assembly and dissociating from the membrane during infectivity for nuclear targeting of the preintegration complex. Membrane release is triggered by proteolytic cleavage of Gag, and it has, until now, been believed that proteolysis induces a conformational change in myr-MA that sequesters the myristyl group. NMR studies reported here reveal that myr-MA adopts myr-exposed [myr(e)] and -sequestered [myr(s)] states, as anticipated. Unexpectedly, the tertiary structures of the protein in both states are very similar, with the sequestered myristyl group occupying a cavity that requires only minor conformational adjustments for insertion. In addition, myristate exposure is coupled with trimerization, with the myristyl group sequestered in the monomer and exposed in the trimer (K-assoc = 2.5 +/- 0.6 x 10(8) M-2). The equilibrium constant is shifted approximate to20-fold toward the trimeric, myristate-exposed species in a Gag-like construct that includes the capsid domain, indicating that exposure is enhanced by Gag subdomains that promote self-association. Our findings indicate that the HIV-1 myristyl switch is regulated not by mechanically induced conformational changes, as observed for other myristyl switches, but instead by entropic modulation of a preexisting equilibrium.
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