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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 Ca(2+) 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 Ca(2+)-signaling during viral processing.

SUBMITTER: Taylor JEN

PROVIDER: S-EPMC3414894 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature

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Calmodulin binds a highly extended HIV-1 MA protein that refolds upon its release.

Taylor James E N JEN Chow John Y H JYH Jeffries Cy M CM Kwan Ann H AH Duff Anthony P AP Hamilton William A WA Trewhella Jill J

Biophysical journal 20120801 3

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 interact ...[more]

PMID: 22947870

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Project description:Backgroundα2-Adrenoceptor agonists are used adjunctively to psychostimulants in treating attention-deficit/hyperactivity disorder (ADHD) when psychostimulants alone do not sufficiently reduce symptoms. However, data on the pharmacokinetic profiles and safety of combination treatments in ADHD are needed.ObjectiveThe primary objective of this study was to evaluate the pharmacokinetic profiles of guanfacine extended release (GXR) and methylphenidate hydrochloride (MPH) extended release, alone and in combination.Study designThis was an open-label, randomized, three-period crossover, drug-drug interaction study.SettingThe study was conducted at a single clinical research center.ParticipantsThirty-eight healthy adults were randomized in this study.InterventionsSubjects were administered single oral doses of GXR (Intuniv(®); Shire Development LLC, Wayne, PA, USA) 4 mg, MPH (Concerta(®); McNeil Pediatrics, Titusville, NJ, USA) 36 mg, or GXR and MPH combined.Main outcome measuresGuanfacine, dexmethylphenidate (d-MPH), and l-methylphenidate (l-MPH) levels were measured with blood samples collected predose and up to 72 h postdose. Safety evaluations included treatment-emergent adverse events (TEAEs), vital signs, and electrocardiograms (ECGs).ResultsThirty-five subjects completed the study. Analyses of the 90 % confidence intervals (CIs) for the geometric mean ratios of the maximum plasma concentration (Cmax) and area under the concentration-time curve extrapolated to infinity (AUC∞) values for guanfacine and d-MPH following administration of GXR or MPH alone or combined met strict bioequivalence criteria (90 % CIs within the interval of 0.80-1.25). Overall, combining GXR and MPH did not alter the pharmacokinetic parameters of either medication. Sixteen subjects (42.1 %) had at least one TEAE. The most commonly reported TEAEs included headache and dizziness following GXR, MPH, and GXR and MPH combined. Two subjects had clinically significant abnormalities in ECG results following coadministration: both events were mild and resolved the same day.ConclusionsIn this short-term, open-label study of healthy adults, coadministration of GXR and MPH did not result in significant pharmacokinetic drug-drug interactions. No unique TEAEs were observed with coadministration of GXR and MPH compared with either treatment alone.

Dataset Information

Calmodulin binds a highly extended HIV-1 MA protein that refolds upon its release.

Publications

Calmodulin binds a highly extended HIV-1 MA protein that refolds upon its release.

Similar Datasets

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