92 research outputs found
Comprehensive structural model of the mechanochemical cycle of a mitotic motor highlights molecular adaptations in the kinesin family
Kinesins are responsible for a wide variety of microtubule-based, ATP-dependent
functions. Their motor domain drives these activities but the molecular adaptations
that specify these diverse and essential cellular activities are poorly understood. It
has been assumed that the first identified kinesin - the transport motor kinesin-1 â is
the mechanistic paradigm for the entire superfamily, but accumulating evidence
suggests that this is not the case. To address the deficits in our understanding of the
molecular basis of functional divergence within the kinesin superfamily, we studied
kinesin-5s, which are essential mitotic motors whose inhibition blocks cell division.
Using cryo-electron microscopy and subnanometer resolution structure
determination, we have visualised conformations of microtubule-bound human
kinesin-5 motor domain at successive steps in its ATPase cycle. Following ATP
hydrolysis, nucleotide-dependent conformational changes in the active site are
allosterically propagated into rotations of the motor domain and uncurling of the drugbinding
loop L5. In addition, the mechanical neck-linker element that is crucial for
motor stepping undergoes discrete, ordered displacements. We also observed large
reorientations of the motor N-terminus that indicate its importance for kinesin-5
function through control of neck-linker conformation. A kinesin-5 mutant lacking this
N-terminus is enzymatically active, and ATP-dependent neck-linker movement and
motility is defective although not ablated. All these aspects of kinesin-5
mechanochemistry are distinct from kinesin-1. Our findings directly demonstrate the
regulatory role of the kinesin-5 N-terminus in collaboration with the motorâs structured
neck-linker, and highlight the multiple adaptations within kinesin motor domains that
tune their mechanochemistries according to distinct functional requirements
Conserved mechanisms of microtubule-stimulated ADP release, ATP binding, and force generation in transport kinesins
Kinesins are a superfamily of microtubule-based ATP-powered motors, important for multiple, essential cellular functions. How microtubule binding stimulates their ATPase and controls force generation is not understood. To address this fundamental question, we visualized microtubule-bound kinesin-1 and kinesin-3 motor domains at multiple steps in their ATPase cycles - including their nucleotide-free states - at ~7Ă
resolution using cryo-electron microscopy. In both motors, microtubule binding promotes ordered conformations of conserved loops that stimulate ADP release, enhance microtubule affinity and prime the catalytic site for ATP binding. ATP binding causes only small shifts of these nucleotide-coordinating loops but induces large conformational changes elsewhere that allow force generation and neck linker docking towards the microtubule plus end. Family-specific differences across the kinesin-microtubule interface account for the distinctive properties of each motor. Our data thus provide evidence for a conserved ATP-driven mechanism for kinesins and reveal the critical mechanistic contribution of the microtubule interface
European security in the 1990s and beyond : the implications of the accession of Cyprus and Malta to the European Union
For the last decade, the dramatic events in eastern and central Europe have (rightly)
dominated the security debate in Europe and, indeed, the wider world. One of the
consequences of this has been that the traditional neglect of the Mediterranean region has
been compounded. However, there are now signs-notably the recent Barcelona conference
at which the European Union's Mediterranean policy was relaunched and extended (to incorporate the grand design of a Mediterranean free trade area) - that the Mediterranean is, at last, receiving some of the attention it deserves and justifies.peer-reviewe
Comprometimento respiratĂłrio secundĂĄrio a acidente ofĂdico crotĂĄlico (Crotalus durissus)
Risk of adverse outcomes associated with cardiac sarcoidosis diagnostic schemes
BackgroundMultiple cardiac sarcoidosis (CS) diagnostic schemes have been published.ObjectivesThis study aims to evaluate the association of different CS diagnostic schemes with adverse outcomes. The diagnostic schemes evaluated were 1993, 2006, and 2017 Japanese criteria and the 2014 Heart Rhythm Society criteria.MethodsData were collected from the Cardiac Sarcoidosis Consortium, an international registry of CS patients. Outcome events were any of the following: all-cause mortality, left ventricular assist device placement, heart transplantation, and appropriate implantable cardioverter-defibrillator therapy. Logistic regression analysis evaluated the association of outcomes with each CS diagnostic scheme.ResultsA total of 587 subjects met the following criteria: 1993 Japanese (n = 310, 52.8%), 2006 Japanese (n = 312, 53.2%), 2014 Heart Rhythm Society (n = 480, 81.8%), and 2017 Japanese (n = 112, 19.1%). Patients who met the 1993 criteria were more likely to experience an event than patients who did not (n = 109 of 310, 35.2% vs n = 59 of 277, 21.3%; OR: 2.00; 95% CI: 1.38-2.90; P P P = 0.18 or OR: 1.51; 95% CI: 0.97-2.33; P = 0.067, respectively).ConclusionsCS patients who met the 1993 and the 2006 criteria had higher odds of adverse clinical outcomes. Future research is needed to prospectively evaluate existing diagnostic schemes and develop new risk models for this complex disease.Cardiolog
Joint analysis of Dark Energy Survey Year 3 data and CMB lensing from SPT and Planck . I. Construction of CMB lensing maps and modeling choices
Joint analyses of cross-correlations between measurements of galaxy positions, galaxy lensing, and lensing of the cosmic microwave background (CMB) offer powerful constraints on the large-scale structure of the Universe. In a forthcoming analysis, we will present cosmological constraints from the analysis of such cross-correlations measured using Year 3 data from the Dark Energy Survey (DES), and CMB data from the South Pole Telescope (SPT) and Planck. Here we present two key ingredients of this analysis: (1) an improved CMB lensing map in the SPT-SZ survey footprint and (2) the analysis methodology that will be used to extract cosmological information from the cross-correlation measurements. Relative to previous lensing maps made from the same CMB observations, we have implemented techniques to remove contamination from the thermal Sunyaev Zelâdovich effect, enabling the extraction of cosmological information from smaller angular scales of the cross-correlation measurements than in previous analyses with DES Year 1 data. We describe our model for the cross-correlations between these maps and DES data, and validate our modeling choices to demonstrate the robustness of our analysis. We then forecast the expected cosmological constraints from the galaxy survey-CMB lensing auto and cross-correlations. We find that the galaxy-CMB lensing and galaxy shear-CMB lensing correlations will on their own provide a constraint on
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at the few percent level, providing a powerful consistency check for the DES-only constraints. We explore scenarios where external priors on shear calibration are removed, finding that the joint analysis of CMB lensing cross-correlations can provide constraints on the shear calibration amplitude at the 5% to 10% level
Joint analysis of Dark Energy Survey Year 3 data and CMB lensing from SPT and Planck . II. Cross-correlation measurements and cosmological constraints
Cross-correlations of galaxy positions and galaxy shears with maps of gravitational lensing of the cosmic microwave background (CMB) are sensitive to the distribution of large-scale structure in the Universe. Such cross-correlations are also expected to be immune to some of the systematic effects that complicate correlation measurements internal to galaxy surveys. We present measurements and modeling of the cross-correlations between galaxy positions and galaxy lensing measured in the first three years of data from the Dark Energy Survey with CMB lensing maps derived from a combination of data from the
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SPT-SZ survey conducted with the South Pole Telescope and full-sky data from the Planck satellite. The CMB lensing maps used in this analysis have been constructed in a way that minimizes biases from the thermal Sunyaev Zelâdovich effect, making them well suited for cross-correlation studies. The total signal-to-noise of the cross-correlation measurements is 23.9 (25.7) when using a choice of angular scales optimized for a linear (nonlinear) galaxy bias model. We use the cross-correlation measurements to obtain constraints on cosmological parameters. For our fiducial galaxy sample, which consist of four bins of magnitude-selected galaxies, we find constraints of
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and
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and
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) when assuming linear (nonlinear) galaxy bias in our modeling. Considering only the cross-correlation of galaxy shear with CMB lensing, we find
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and
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. Our constraints on
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are consistent with recent cosmic shear measurements, but lower than the values preferred by primary CMB measurements from Planck
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