scholarly journals A DNA translocase operates by cycling between planar and lock-washer structures

2020 ◽  
Author(s):  
Juan P. Castillo ◽  
Alexander Tong ◽  
Sara Tafoya ◽  
Paul J. Jardine ◽  
Carlos Bustamante
Keyword(s):  
Helical Structure ◽  
Power Stroke ◽  
Load Bearing ◽  
Planar Form ◽  
Full Turn ◽  
Translocation Mechanism ◽  
Disordered Polymers ◽  
Dna Translocase

Ring ATPases that translocate disordered polymers possess lock-washer architectures that they impose on their substrates during transport via a hand-over-hand mechanism. Here, we investigate the operation of ring motors that transport substrates possessing a preexisting helical structure, such as the bacteriophage ϕ29 dsDNA packaging motor. During each cycle, this pentameric motor tracks one helix strand (the ‘tracking strand’), and alternates between two segregated phases: a dwell in which it exchanges ADP for ATP and a burst in which it packages a full turn of DNA in four steps. We challenge this motor with DNA-RNA hybrids and dsRNA substrates and find that it adapts the size of its burst to the corresponding shorter helical pitches by keeping three of its power strokes invariant while shortening the fourth. Intermittently, the motor loses grip when the tracking strand is RNA, indicating that it makes load-bearing contacts with the substrate that are optimal with dsDNA. The motor possesses weaker grip when ADP-bound at the end of the burst. To rationalize all these observations, we propose a helical inchworm translocation mechanism in which the motor increasingly adopts a lock-washer structure during the ATP loading dwell and successively regains its planar form with each power stroke during the burst.

scholarly journals A DNA packaging motor inchworms along one strand allowing it to adapt to alternative double-helical structures

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Juan P. Castillo ◽  
Alexander B. Tong ◽  
Sara Tafoya ◽  
Paul J. Jardine ◽  
Carlos Bustamante
Keyword(s):  
Dna Packaging ◽  
Power Stroke ◽  
Helical Structures ◽  
Load Bearing ◽  
Planar Form ◽  
Optimal Load ◽  
Dna Packaging Motor ◽  
Translocation Mechanism ◽  
Disordered Polymers

AbstractRing ATPases that translocate disordered polymers possess lock-washer architectures that they impose on their substrates during transport via a hand-over-hand mechanism. Here, we investigate the operation of ring motors that transport ordered, helical substrates, such as the bacteriophage ϕ29 dsDNA packaging motor. This pentameric motor alternates between an ATP loading dwell and a hydrolysis burst wherein it packages one turn of DNA in four steps. When challenged with DNA-RNA hybrids and dsRNA, the motor matches its burst to the shorter helical pitches, keeping three power strokes invariant while shortening the fourth. Intermittently, the motor loses grip on the RNA-containing substrates, indicating that it makes optimal load-bearing contacts with dsDNA. To rationalize these observations, we propose a helical inchworm translocation mechanism in which, during each cycle, the motor increasingly adopts a lock-washer structure during the ATP loading dwell and successively regains its planar form with each power stroke during the burst.

Ciliary coordination in newt lung cells requires microtubule-based linkages between basal bodies: A correlative light and EM study

1992 ◽  
Vol 50 (1) ◽  
pp. 570-571
Author(s):  
Robert Hard ◽  
Gerald Rupp ◽  
Matthew L. Withiam-Leitch ◽  
Lisa Cardamone
Keyword(s):  
Basal Body ◽  
Untreated Control ◽  
Beat Frequency ◽  
Primary Cultures ◽  
Living Cells ◽  
Power Stroke ◽  
Ultrastructural Changes ◽  
Lung Cells ◽  
Basal Bodies ◽  
Ciliated Cells

In a coordinated field of beating cilia, the direction of the power stroke is correlated with the orientation of basal body appendages, called basal feet. In newt lung ciliated cells, adjacent basal feet are interconnected by cold-stable microtubules (basal MTs). In the present study, we investigate the hypothesis that these basal MTs stabilize ciliary distribution and alignment. To accomplish this, newt lung primary cultures were treated with the microtubule disrupting agent, Colcemid. In newt lung cultures, cilia normally disperse in a characteristic fashion as the mucociliary epithelium migrates from the tissue explant. Four arbitrary, but progressive stages of dispersion were defined and used to monitor this redistribution process. Ciliaiy beat frequency, coordination, and dispersion were assessed for 91 hrs in untreated (control) and treated cultures. When compared to controls, cilia dispersed more rapidly and ciliary coordination decreased markedly in cultures treated with Colcemid (2 mM). Correlative LM/EM was used to assess whether these effects of Colcemid were coupled to ultrastructural changes. Living cells were defined as having coordinated or uncoordinated cilia and then were processed for transmission EM.

Single molecule optical diffraction: A tool for understanding the structure of triple stranded left-hand helical cellulose

1989 ◽  
Vol 47 ◽  
pp. 1024-1025
Author(s):  
George C. Ruben ◽  
William Krakow
Keyword(s):  
Single Molecule ◽  
Helical Structure ◽  
Optical Diffraction ◽  
Maximum Diameter ◽  
Primary Cell Wall ◽  
Cellulose Synthesis ◽  
Left Hand ◽  
Left Handed ◽  
Freeze Dried ◽  
Diffraction Patterns

Tobacco primary cell wall and normal bacterial Acetobacter xylinum cellulose formation produced a 36.8±3Å triple-stranded left-hand helical microfibril in freeze-dried Pt-C replicas and in negatively stained preparations for TEM. As three submicrofibril strands exit the wall of Axylinum , they twist together to form a left-hand helical microfibril. This process is driven by the left-hand helical structure of the submicrofibril and by cellulose synthesis. That is, as the submicrofibril is elongating at the wall, it is also being left-hand twisted and twisted together with two other submicrofibrils. The submicrofibril appears to have the dimensions of a nine (l-4)-ß-D-glucan parallel chain crystalline unit whose long, 23Å, and short, 19Å, diagonals form major and minor left-handed axial surface ridges every 36Å.The computer generated optical diffraction of this model and its corresponding image have been compared. The submicrofibril model was used to construct a microfibril model. This model and corresponding microfibril images have also been optically diffracted and comparedIn this paper we compare two less complex microfibril models. The first model (Fig. 1a) is constructed with cylindrical submicrofibrils. The second model (Fig. 2a) is also constructed with three submicrofibrils but with a single 23 Å diagonal, projecting from a rounded cross section and left-hand helically twisted, with a 36Å repeat, similar to the original model (45°±10° crossover angle). The submicrofibrils cross the microfibril axis at roughly a 45°±10° angle, the same crossover angle observed in microflbril TEM images. These models were constructed so that the maximum diameter of the submicrofibrils was 23Å and the overall microfibril diameters were similar to Pt-C coated image diameters of ∼50Å and not the actual diameter of 36.5Å. The methods for computing optical diffraction patterns have been published before.

Load-Bearing in the Ovine Medial Tibial Condyle: Effect of Meniscectomy

1993 ◽  
Vol 06 (02) ◽  
pp. 100-104 ◽  
Author(s):  
D. M. Pickles ◽  
C. R. Bellenger
Keyword(s):  
Knee Joint ◽  
Contact Area ◽  
Mammalian Species ◽  
Total Removal ◽  
Load Bearing ◽  
Human Knee ◽  
Biochemical Effects ◽  
Pressure Sensitive ◽  
Medial Meniscectomy ◽  
Tibial Condyle

SummaryTotal removal of a knee joint meniscus is followed by osteoarthritis in many mammalian species. Altered load-bearing has been observed in the human knee following meniscectomy but less is known about biochemical effects of meniscectomy in other species. Using pressure sensitive paper in sheep knee (stifle) joints it was found that, for comparable loads, the load-bearing area on the medial tibial condyle was significantly reduced following medial meniscectomy. Also, for loads of between 50 N and 500 N applied to the whole joint, the slope of the regression of contact area against load was much smaller. Following medial meniscectomy, the ability to increase contact area as load increased was markedly reduced.The load bearing area on the medial tibial condyle was reduced following meniscectomy.

Effect of long-term loading on timber load-bearing elements

2015 ◽  
Vol 10 (2) ◽  
pp. 25-34
Author(s):  
Kristian Sogel
Keyword(s):  
Load Bearing

PARTICULAR QUALITIES OF CONSTRUCTION AND TECHNICAL EXPERTISE OF STRUCTURES AGRICULTURAL WAREHOUSE OF MINERAL FERTILIZERS

2020 ◽  
Author(s):  
I.O. Egorochkina ◽  
◽  
I.A. Serebryanaya ◽  
S. A. Jamaldinov ◽  
F.A. Bataeva ◽  
...  
Keyword(s):  
Functional State ◽  
Mineral Fertilizers ◽  
Technical Expertise ◽  
Technical Documentation ◽  
Load Bearing ◽  
Building Load

The article describes the features of construction and technical expertise of structures of agricultural warehouse of mineral fertilizers. A draft program for visual and detailed instrumental inspection of building load-bearing structures has been developed. In accordance with the recommendations of the regulatory and technical documentation, measures have been developed to repair and restore the functional state of damaged structures.

SYNTHESIS OF ELEMENTS OF LOAD-BEARING SYSTEMS WITH A GIVEN LEVEL OF RELIABILITY

2020 ◽  
Author(s):  
Y.P. Manshin ◽  
◽  
E.Yu. Manshina ◽  
Keyword(s):  
Strain Measurement ◽  
Field Strain ◽  
Design Element ◽  
Load Bearing ◽  
Cyclic Bending ◽  
Bending Stresses

The article considers an algorithm for analyzing the results of field strain-measurement studies of machine structures, which allows obtaining data for the modernization of elements in the form of coefficients of parameter changes. As the object of application of the method, the design element of the header was selected, which had failures due to insufficient endurance under cyclic bending stresses.

Liquid Crystal Trimers Incorporating Saturated Isosteres of Benzene and Exhibiting Modulated Nematic Phases

2019 ◽  
Author(s):  
Adam Al-Janabi ◽  
Richard Mandle
Keyword(s):  
Liquid Crystal ◽  
Helical Structure ◽  
Molecular Shape ◽  
Saturated Hydrocarbons ◽  
Fluid System ◽  
Structural Requirement ◽  
Disubstituted Benzene ◽  
Bona Fide ◽  
Nematic Phases ◽  
Bend Angles

<p>The nematic twist-bend (N<sub>TB</sub>) liquid crystal phase possesses a local helical structure with a pitch length of a few nanometres and is the first example of spontaneous symmetry breaking in a fluid system. All known examples of the N­<sub>TB­</sub> phase occur in materials whose constituent mesogenic units are aromatic hydrocarbons. It is not clear if this is due to synthetic convenience or a <i>bona fide</i> structural requirement for a material to exhibit this phase of matter. In this work we demonstrate that materials consisting largely of saturated hydrocarbons could also give rise to this mesophase. Furthermore, replacement of 1,4-disubstituted benzene with <i>trans</i> 1,4-cyclohexane or even 1,4-cubane does not especially alter the transition temperatures of the resulting material nor does it appear to impact upon the heliconical tilt angle, suggesting the local structure of the phase is unperturbed. Calculating the probability distribution of bend angles reveals that the choice of isosteric group has little impact on the overall molecular shape, demonstrating the shape-driven nature of the N<sub>TB</sub> phase. </p>

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