scholarly journals Distribution of first-reaction times with target regions on boundaries of shell-like domains

2021 ◽  
Author(s):  
Denis Grebenkov ◽  
Ralf Metzler ◽  
Gleb Oshanin
Keyword(s):  
Signal Transduction ◽  
Reaction Times ◽  
Target Region ◽  
Multi Stage ◽  
Approximate Form ◽  
Concentric Spheres ◽  
Molecular Signal ◽  
Membrane Bound ◽  
Escape Problem ◽  
Shell Geometry

Abstract We study the probability density function (PDF) of the first-reaction times between a diffusive ligand and a membrane-bound, immobile imperfect target region in a restricted "onion-shell" geometry bounded by two nested membranes of arbitrary shapes. For such a setting, encountered in diverse molecular signal transduction pathways or in the narrow escape problem with additional steric constraints, we derive an exact spectral form of the PDF, as well as present its approximate form calculated by help of the so-called self-consistent approximation. For a particular case when the nested domains are concentric spheres, we get a fully explicit form of the approximated PDF, assess the accuracy of this approximation, and discuss various facets of the obtained distributions. Our results can be straightforwardly applied to describe the PDF of the terminal reaction event in multi-stage signal transduction processes.

The effect of overall stimulus velocity on motion parallax

2008 ◽  
Vol 25 (1) ◽  
pp. 3-15 ◽  
Author(s):  
YING ZHANG ◽  
PETER H. SCHILLER
Keyword(s):  
Motion Parallax ◽  
Three Dimensional ◽  
Reaction Times ◽  
Visual Display ◽  
Stimulus Movement ◽  
Stimulus Velocity ◽  
Target Region ◽  
Performance Accuracy ◽  
Dimensional Object

This study examined the effectiveness with which motion parallax information can be utilized by rhesus monkeys for depth perception. A visual display comprised of random-dots that mimicked a rigid, three-dimensional object rocking back and forth was used. Differential depth was produced by presenting sub-regions of the dots moving at different velocities from the rest of dots in the display. The tasks for the monkeys were to detect or discriminate a target region that was protruding the furthest from the background plane. To understand the role of stimulus movement, we examined the accuracy and the rapidity of the saccadic responses as a function of rocking velocity of the entire three-dimensional object. The results showed that performance accuracy improved and reaction times decreased with increasing rocking velocities. The monkeys can process the motion parallax information with remarkable rapidity such that the average reaction time ranged between 212 and 246 milliseconds. The data collected suggest that the successive activation of just two sets of cones is sufficient to perform the task.

scholarly journals It takes two transducins to activate the cGMP-phosphodiesterase 6 in retinal rods

Open Biology ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 180075 ◽  
Author(s):  
Bilal M. Qureshi ◽  
Elmar Behrmann ◽  
Johannes Schöneberg ◽  
Justus Loerke ◽  
Jörg Bürger ◽  
...  
Keyword(s):  
Signal Transduction ◽  
G Protein ◽  
Reaction Diffusion ◽  
Structural Data ◽  
Functional Asymmetry ◽  
Activation Mechanism ◽  
Visual Signal ◽  
Local Concentration ◽  
Retinal Rods ◽  
Membrane Bound

Among cyclic nucleotide phosphodiesterases (PDEs), PDE6 is unique in serving as an effector enzyme in G protein-coupled signal transduction. In retinal rods and cones, PDE6 is membrane-bound and activated to hydrolyse its substrate, cGMP, by binding of two active G protein α-subunits (Gα*). To investigate the activation mechanism of mammalian rod PDE6, we have collected functional and structural data, and analysed them by reaction–diffusion simulations. Gα* titration of membrane-bound PDE6 reveals a strong functional asymmetry of the enzyme with respect to the affinity of Gα* for its two binding sites on membrane-bound PDE6 and the enzymatic activity of the intermediary 1 : 1 Gα* · PDE6 complex. Employing cGMP and its 8-bromo analogue as substrates, we find that Gα* · PDE6 forms with high affinity but has virtually no cGMP hydrolytic activity. To fully activate PDE6, it takes a second copy of Gα* which binds with lower affinity, forming Gα* · PDE6 · Gα*. Reaction–diffusion simulations show that the functional asymmetry of membrane-bound PDE6 constitutes a coincidence switch and explains the lack of G protein-related noise in visual signal transduction. The high local concentration of Gα* generated by a light-activated rhodopsin molecule efficiently activates PDE6, whereas the low density of spontaneously activated Gα* fails to activate the effector enzyme.

scholarly journals Identification of Proteins Likely To Be Involved in Morphogenesis, Cell Division, and Signal Transduction in Planctomycetes by Comparative Genomics

2012 ◽  
Vol 194 (23) ◽  
pp. 6419-6430 ◽  
Author(s):  
Christian Jogler ◽  
Jost Waldmann ◽  
Xiaoluo Huang ◽  
Mareike Jogler ◽  
Frank Oliver Glöckner ◽  
...  
Keyword(s):  
Signal Transduction ◽  
Cell Division ◽  
Model Organisms ◽  
Genetic Studies ◽  
Content Type ◽  
Life Styles ◽  
Membrane Bound ◽  
Guilt By Association ◽  
Complex Signaling ◽  
Signal Transduction Systems

ABSTRACTMembers of thePlanctomycetesclade share many unusual features for bacteria. Their cytoplasm contains membrane-bound compartments, they lack peptidoglycan and FtsZ, they divide by polar budding, and they are capable of endocytosis. Planctomycete genomes have remained enigmatic, generally being quite large (up to 9 Mb), and on average, 55% of their predicted proteins are of unknown function. Importantly, proteins related to the unusual traits ofPlanctomycetesremain largely unknown. Thus, we embarked on bioinformatic analyses of these genomes in an effort to predict proteins that are likely to be involved in compartmentalization, cell division, and signal transduction. We used three complementary strategies. First, we defined thePlanctomycetescore genome and subtracted genes of well-studied model organisms. Second, we analyzed the gene content and synteny of morphogenesis and cell division genes and combined both methods using a “guilt-by-association” approach. Third, we identified signal transduction systems as well as sigma factors. These analyses provide a manageable list of candidate genes for future genetic studies and provide evidence for complex signaling in thePlanctomycetesakin to that observed for bacteria with complex life-styles, such asMyxococcus xanthus.

Sign in / Sign up

Export Citation Format

Share Document