title: Entropic switch regulates myristate exposure in the HIV-1 matrix protein.
abstract: 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 approximately 20-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.
authors.affiliation: Howard Hughes Medical Institute and Department of Chemistry and Biochemistry, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250-5398, USA.
authors.forename: Chun
authors.initials: C
authors.lastname: Tang
authors.forename: Erin
authors.initials: E
authors.lastname: Loeliger
authors.forename: Paz
authors.initials: P
authors.lastname: Luncsford
authors.forename: Isaac
authors.initials: I
authors.lastname: Kinde
authors.forename: Dorothy
authors.initials: D
authors.lastname: Beckett
authors.forename: Michael F
authors.initials: MF
authors.lastname: Summers
mesh_terms: D015683:Gene Products, gag / Q000737:chemistry / Q000187:drug effects*; D015488:HIV Antigens / Q000737:chemistry / Q000187:drug effects*; D008958:Models, Molecular; D019814:Myristic Acid / Q000494:pharmacology*; D011487:Protein Conformation; D013816:Thermodynamics; D014764:Viral Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus
chemical_list: D015683:Gene Products, gag; D015488:HIV Antigens; D014764:Viral Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus; C054858:p17 protein, Human Immunodeficiency Virus Type 1; D019814:Myristic Acid