Calcium regulation of myosin-I tension sensing.

Pennsylvania Muscle Institute and Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Biophysical Journal (Impact Factor: 3.83). 06/2012; 102(12):2799-807. DOI: 10.1016/j.bpj.2012.05.014
Source: PubMed

ABSTRACT Myo1b is a myosin that is exquisitely sensitive to tension. Its actin-attachment lifetime increases > 50-fold when its working stroke is opposed by 1 pN of force. The long attachment lifetime of myo1b under load raises the question: how are actin attachments that last >50 s in the presence of force regulated? Like most myosins, forces are transmitted to the myo1b motor through a light-chain binding domain that is structurally stabilized by calmodulin, a calcium-binding protein. Thus, we examined the effect of calcium on myo1b motility using ensemble and single-molecule techniques. Calcium accelerates key biochemical transitions on the ATPase pathway, decreases the working-stroke displacement, and greatly reduces the ability of myo1b to sense tension. Thus, calcium provides an effective mechanism for inhibiting motility and terminating long-duration attachments.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Class I myosins can sense cellular mechanical forces and function as tension-sensitive anchors or transporters. How mechanical load is transduced from the membrane-binding tail to the force-generating head in myosin-1 is unknown. Here we determined the crystal structure of the entire tail of mouse myosin-1c in complex with apocalmodulin, showing that myosin-1c adopts a stable monomer conformation suited for force transduction. The lever-arm helix and the C-terminal extended PH domain of the motor are coupled by a stable post-IQ domain bound to calmodulin in a highly unusual mode. Ca(2+) binding to calmodulin induces major conformational changes in both IQ motifs and the post-IQ domain and increases flexibility of the myosin-1c tail. Our study provides a structural blueprint for the neck and tail domains of myosin-1 and expands the target binding modes of the master Ca(2+)-signal regulator calmodulin.
    Nature Structural & Molecular Biology 12/2014; DOI:10.1038/nsmb.2923 · 11.63 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Most sounds of interest consist of complex, time-dependent admixtures of tones of diverse frequencies and variable amplitudes. To detect and process these signals, the ear employs a highly nonlinear, adaptive, real-time spectral analyzer: the cochlea. Sound excites vibration of the eardrum and the three miniscule bones of the middle ear, the last of which acts as a piston to initiate oscillatory pressure changes within the liquid-filled chambers of the cochlea. The basilar membrane, an elastic band spiraling along the cochlea between two of these chambers, responds to these pressures by conducting a largely independent traveling wave for each frequency component of the input. Because the basilar membrane is graded in mass and stiffness along its length, however, each traveling wave grows in magnitude and decreases in wavelength until it peaks at a specific, frequency-dependent position: low frequencies propagate to the cochlear apex, whereas high frequencies culminate at the base. The oscillations of the basilar membrane deflect hair bundles, the mechanically sensitive organelles of the ear's sensory receptors, the hair cells. As mechanically sensitive ion channels open and close, each hair cell responds with an electrical signal that is chemically transmitted to an afferent nerve fiber and thence into the brain. In addition to transducing mechanical inputs, hair cells amplify them by two means. Channel gating endows a hair bundle with negative stiffness, an instability that interacts with the motor protein myosin-1c to produce a mechanical amplifier and oscillator. Acting through the piezoelectric membrane protein prestin, electrical responses also cause outer hair cells to elongate and shorten, thus pumping energy into the basilar membrane's movements. The two forms of motility constitute an active process that amplifies mechanical inputs, sharpens frequency discrimination, and confers a compressive nonlinearity on responsiveness. These features arise because the active process operates near a Hopf bifurcation, the generic properties of which explain several key features of hearing. Moreover, when the gain of the active process rises sufficiently in ultraquiet circumstances, the system traverses the bifurcation and even a normal ear actually emits sound. The remarkable properties of hearing thus stem from the propagation of traveling waves on a nonlinear and excitable medium.
    Reports on Progress in Physics 07/2014; 77(7):076601. DOI:10.1088/0034-4885/77/7/076601 · 15.63 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Extract of Acanthopanax senticosus harms (EAS) has been shown to have neuroprotective effects on Parkinson's disease (PD) cell model against α-synuclein overexpression and toxicity. However, studies of its anti-PD mechanism are challenging, owing to the complex pathophysiology of PD, and complexity of EAS with multiple constituents acting on different proteomic pathways. Here, we have investigated the proteomic profiles and potential biomarkers in a cell model of A53T mutant α-synuclein (A53T-α-Syn) overexpression after treatment of EAS. Using an iTRAQ (isobaric tags for relative and absolute quantitation)-based proteomics research approach, we identified 3425 modulated proteins, out of which 84 were found to be altered by A53T-α-Syn and considered as potential biomarkers. After treatment with EAS, the group showed the tendency to correct the abnormal expressions of 16 proteins out of 84 potential biomarkers, which were associated with the formation of Lewy body, mitochondrial energy metabolism, protein synthesis and apoptosis, etc. This study indicated that EAS might be a promising candidate for prevention or treatment of PD by regulating the related proteomic pathways in A53T-α-Syn transgenic SH-SY5Y cells.
    Neurochemistry International 04/2014; DOI:10.1016/j.neuint.2014.04.012 · 2.65 Impact Factor