title: Calmodulin binds a highly extended HIV-1 MA protein that refolds upon its release.
abstract: Calmodulin (CaM) expression is upregulated upon HIV-1 infection and interacts with proteins involved in viral processing, including the multifunctional HIV-1 MA protein. We present here the results of studies utilizing small-angle neutron scattering with contrast variation that, when considered in the light of earlier fluorescence and NMR data, show CaM binds MA in an extended open-clamp conformation via interactions with two tryptophans that are widely spaced in sequence and space. The interaction requires a disruption of the MA tertiary fold such that MA becomes highly extended in a long snakelike conformation. The CaM-MA interface is extensive, covering ~70% of the length of the MA such that regions known to be important in MA interactions with critical binding partners would be impacted. The CaM conformation is semiextended and as such is distinct from the classical CaM-collapse about short α-helical targets. NMR data show that upon dissociation of the CaM-MA complex, either by the removal of Ca2+or increasing ionic strength, MA reforms its native tertiary contacts. Thus, we observe a high level of structural plasticity in MA that may facilitate regulation of its activities via intracellular Ca2+-signaling during viral processing.
authors.affiliation: Bragg Institute, Australian Nuclear Science and Technology Organisation, New South Wales, Australia; School of Molecular Bioscience, The University of Sydney, New South Wales, Australia.
authors.forename: James E N
authors.initials: JEN
authors.lastname: Taylor
authors.affiliation: School of Molecular Bioscience, The University of Sydney, New South Wales, Australia.
authors.forename: John Y H
authors.initials: JYH
authors.lastname: Chow
authors.affiliation: School of Molecular Bioscience, The University of Sydney, New South Wales, Australia.
authors.forename: Cy M
authors.initials: CM
authors.lastname: Jeffries
authors.affiliation: School of Molecular Bioscience, The University of Sydney, New South Wales, Australia.
authors.forename: Ann H
authors.initials: AH
authors.lastname: Kwan
authors.affiliation: Bragg Institute, Australian Nuclear Science and Technology Organisation, New South Wales, Australia.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Duff
authors.affiliation: Bragg Institute, Australian Nuclear Science and Technology Organisation, New South Wales, Australia.
authors.forename: William A
authors.initials: WA
authors.lastname: Hamilton
authors.affiliation: School of Molecular Bioscience, The University of Sydney, New South Wales, Australia. Electronic address: jill.trewhella@sydney.edu.au.
authors.forename: Jill
authors.initials: J
authors.lastname: Trewhella
mesh_terms: D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D015488:HIV Antigens / Q000737:chemistry* / Q000378:metabolism*; D015497:HIV-1; D008958:Models, Molecular; D033363:Neutron Diffraction; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D011487:Protein Conformation; D058849:Protein Refolding; D053838:Scattering, Small Angle; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D015488:HIV Antigens; D054301:gag Gene Products, Human Immunodeficiency Virus; C054858:p17 protein, Human Immunodeficiency Virus Type 1