scholarly journals Anisotropy in mechanical unfolding of protein upon partner-assisted pulling and handle-assisted pulling

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Nisha Arora ◽  
Jagadish Prasad Hazra ◽  
Sabyasachi Rakshit
Keyword(s):  
Single Molecule ◽  
Complex Geometry ◽  
Protein Complexes ◽  
Dynamic Network ◽  
Force Sensing ◽  
Force Sensors ◽  
Mechanical Responses ◽  
End To End ◽  
Potential Energy Landscapes ◽  
Cadherin 23

AbstractProteins as force-sensors respond to mechanical cues and regulate signaling in physiology. Proteins commonly connect the source and response points of mechanical cues in two conformations, independent proteins in end-to-end geometry and protein complexes in handshake geometry. The force-responsive property of independent proteins in end-to-end geometry is studied extensively using single-molecule force spectroscopy (SMFS). The physiological significance of the complex conformations in force-sensing is often disregarded as mere surge protectors. However, with the potential of force-steering, protein complexes possess a distinct mechano-responsive property over individual force-sensors. To decipher, we choose a force-sensing protein, cadherin-23, from tip-link complex and perform SMFS using end-to-end geometry and handshake complex geometry. We measure higher force-resilience of cadherin-23 with preferential shorter extensions in handshake mode of pulling over the direct mode. The handshake geometry drives the force-response of cadherin-23 through different potential-energy landscapes than direct pulling. Analysis of the dynamic network structure of cadherin-23 under tension indicates narrow force-distributions among residues in cadherin-23 in direct pulling, resulting in low force-dissipation paths and low resilience to force. Overall, the distinct and superior mechanical responses of cadherin-23 in handshake geometry than single protein geometry highlight a probable evolutionary drive of protein-protein complexes as force-conveyors over independent ones.

scholarly journals Fast Diffusion of the Unassembled PetC1-GFP Protein in the Cyanobacterial Thylakoid Membrane

Life ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 15
Author(s):  
Radek Kaňa ◽  
Gábor Steinbach ◽  
Roman Sobotka ◽  
György Vámosi ◽  
Josef Komenda
Keyword(s):  
Membrane Proteins ◽  
Single Molecule ◽  
Protein Interactions ◽  
Thylakoid Membrane ◽  
Protein Complexes ◽  
Correlation Spectroscopy ◽  
Membrane Microdomains ◽  
Fast Diffusion ◽  
Light Harvesting Complexes ◽  
Term Survival

Biological membranes were originally described as a fluid mosaic with uniform distribution of proteins and lipids. Later, heterogeneous membrane areas were found in many membrane systems including cyanobacterial thylakoids. In fact, cyanobacterial pigment–protein complexes (photosystems, phycobilisomes) form a heterogeneous mosaic of thylakoid membrane microdomains (MDs) restricting protein mobility. The trafficking of membrane proteins is one of the key factors for long-term survival under stress conditions, for instance during exposure to photoinhibitory light conditions. However, the mobility of unbound ‘free’ proteins in thylakoid membrane is poorly characterized. In this work, we assessed the maximal diffusional ability of a small, unbound thylakoid membrane protein by semi-single molecule FCS (fluorescence correlation spectroscopy) method in the cyanobacterium Synechocystis sp. PCC6803. We utilized a GFP-tagged variant of the cytochrome b6f subunit PetC1 (PetC1-GFP), which was not assembled in the b6f complex due to the presence of the tag. Subsequent FCS measurements have identified a very fast diffusion of the PetC1-GFP protein in the thylakoid membrane (D = 0.14 − 2.95 µm2s−1). This means that the mobility of PetC1-GFP was comparable with that of free lipids and was 50–500 times higher in comparison to the mobility of proteins (e.g., IsiA, LHCII—light-harvesting complexes of PSII) naturally associated with larger thylakoid membrane complexes like photosystems. Our results thus demonstrate the ability of free thylakoid-membrane proteins to move very fast, revealing the crucial role of protein–protein interactions in the mobility restrictions for large thylakoid protein complexes.

scholarly journals Contribution of low-temperature single-molecule techniques to structural issues of pigment–protein complexes from photosynthetic purple bacteria

2018 ◽  
Vol 15 (138) ◽  
pp. 20170680 ◽  
Author(s):  
Alexander Löhner ◽  
Richard Cogdell ◽  
Jürgen Köhler
Keyword(s):  
Low Temperature ◽  
Single Molecule ◽  
Degrees Of Freedom ◽  
Protein Complexes ◽  
Purple Bacteria ◽  
Structural Models ◽  
Spectral Features ◽  
Light Harvesting Complexes ◽  
Pigment Protein Complexes ◽  
Photosynthetic Purple Bacteria

As the electronic energies of the chromophores in a pigment–protein complex are imposed by the geometrical structure of the protein, this allows the spectral information obtained to be compared with predictions derived from structural models. Thereby, the single-molecule approach is particularly suited for the elucidation of specific, distinctive spectral features that are key for a particular model structure, and that would not be observable in ensemble-averaged spectra due to the heterogeneity of the biological objects. In this concise review, we illustrate with the example of the light-harvesting complexes from photosynthetic purple bacteria how results from low-temperature single-molecule spectroscopy can be used to discriminate between different structural models. Thereby the low-temperature approach provides two advantages: (i) owing to the negligible photobleaching, very long observation times become possible, and more importantly, (ii) at cryogenic temperatures, vibrational degrees of freedom are frozen out, leading to sharper spectral features and in turn to better resolved spectra.

Assembly and Dynamics of the Bacterial Flagellum

2020 ◽  
Vol 74 (1) ◽  
pp. 181-200 ◽  
Author(s):  
Judith P. Armitage ◽  
Richard M. Berry
Keyword(s):  
Single Molecule ◽  
Protein Complexes ◽  
Complex Structure ◽  
Live Cells ◽  
Flagellar Motor ◽  
Interacting Protein ◽  
Bacterial Flagellum ◽  
Bacterial Flagellar Motor ◽  
The Stability

The bacterial flagellar motor is the most complex structure in the bacterial cell, driving the ion-driven rotation of the helical flagellum. The ordered expression of the regulon and the assembly of the series of interacting protein rings, spanning the inner and outer membranes to form the ∼45–50-nm protein complex, have made investigation of the structure and mechanism a major challenge since its recognition as a rotating nanomachine about 40 years ago. Painstaking molecular genetics, biochemistry, and electron microscopy revealed a tiny electric motor spinning in the bacterial membrane. Over the last decade, new single-molecule and in vivo biophysical methods have allowed investigation of the stability of this and other large protein complexes, working in their natural environment inside live cells. This has revealed that in the bacterial flagellar motor, protein molecules in both the rotor and stator exchange with freely circulating pools of spares on a timescale of minutes, even while motors are continuously rotating. This constant exchange has allowed the evolution of modified components allowing bacteria to keep swimming as the viscosity or the ion composition of the outside environment changes.

scholarly journals Broken force dispersal network in tip-links by the mutations at the Ca2+-binding residues induces hearing-loss

2019 ◽  
Vol 476 (16) ◽  
pp. 2411-2425 ◽  
Author(s):  
Jagadish P. Hazra ◽  
Amin Sagar ◽  
Nisha Arora ◽  
Debadutta Deb ◽  
Simerpreet Kaur ◽  
...  
Keyword(s):  
Hearing Loss ◽  
Inner Ear ◽  
Single Molecule ◽  
Force Sensor ◽  
Force Sensors ◽  
Single Molecule Level ◽  
Conformational Variability ◽  
Atomic Force ◽  
Wide Range ◽  
And Function

Abstract Tip-link as force-sensor in hearing conveys the mechanical force originating from sound to ion-channels while maintaining the integrity of the entire sensory assembly in the inner ear. This delicate balance between structure and function of tip-links is regulated by Ca2+-ions present in endolymph. Mutations at the Ca2+-binding sites of tip-links often lead to congenital deafness, sometimes syndromic defects impairing vision along with hearing. Although such mutations are already identified, it is still not clear how the mutants alter the structure-function properties of the force-sensors associated with diseases. With an aim to decipher the differences in force-conveying properties of the force-sensors in molecular details, we identified the conformational variability of mutant and wild-type tip-links at the single-molecule level using FRET at the endolymphatic Ca2+ concentrations and subsequently measured the force-responsive behavior using single-molecule force spectroscopy with an Atomic Force Microscope (AFM). AFM allowed us to mimic the high and wide range of force ramps (103–106 pN s−1) as experienced in the inner ear. We performed in silico network analysis to learn that alterations in the conformations of the mutants interrupt the natural force-propagation paths through the sensors and make the mutant tip-links vulnerable to input forces from sound stimuli. We also demonstrated that a Ca2+ rich environment can restore the force-response of the mutant tip-links which may eventually facilitate the designing of better therapeutic strategies to the hearing loss.

scholarly journals End-to-End Real-Time Demonstration of the Slotted, SDN-Controlled NEPHELE Optical Datacenter Network

Photonics ◽  
2020 ◽  
Vol 7 (2) ◽  
pp. 44
Author(s):  
Konstantinos Tokas ◽  
Giannis Patronas ◽  
Christos Spatharakis ◽  
Paraskevas Bakopoulos ◽  
Angelos Kyriakos ◽  
...  
Keyword(s):  
Real Time ◽  
Cost Efficiency ◽  
High Capacity ◽  
Dynamic Network ◽  
Optical Data ◽  
Dynamic Allocation ◽  
Network Resources ◽  
Datacenter Network ◽  
Software And Hardware ◽  
End To End

The NEPHELE hybrid electro-optical datacenter network (DCN) architecture is proposed as a dynamic network solution to provide high capacity, scalability, and cost efficiency in comparison to the existing DCN infrastructures. The details of the NEPHELE DCN architecture and its various key parts are introduced, and the performance of its implementation is evaluated through an end-to-end NEPHELE demonstrator, which was built at the National Technical University of Athens. Several communication scenarios are demonstrated in real time, exploiting a scalable optical data-plane architecture with a software-defined network (SDN) control plane capable of slotted operation for dynamic allocation of network resources. Real-time end-to-end functionality and integration of various software and hardware components are verified in a six-host prototype datacenter cluster.

Sign in / Sign up

Export Citation Format

Share Document