scholarly journals Calcium can mobilize and activate myosin-VI

2016 ◽  
Vol 113 (9) ◽  
pp. E1162-E1169 ◽  
Author(s):  
Christopher Batters ◽  
Dario Brack ◽  
Heike Ellrich ◽  
Beate Averbeck ◽  
Claudia Veigel
Keyword(s):  
Binding Site ◽  
Calcium Binding ◽  
Calcium Flux ◽  
Particle Analysis ◽  
Myosin Vi ◽  
Electron Microscopic ◽  
Iq Motif ◽  
Lever Arm ◽  
High Calcium ◽  
Wide Range

The ability to coordinate the timing of motor protein activation lies at the center of a wide range of cellular motile processes including endocytosis, cell division, and cancer cell migration. We show that calcium dramatically alters the conformation and activity of the myosin-VI motor implicated in pivotal steps of these processes. We resolved the change in motor conformation and in structural flexibility using single particle analysis of electron microscopic data and identified interacting domains using fluorescence spectroscopy. We discovered that calcium binding to calmodulin increases the binding affinity by a factor of 2,500 for a bipartite binding site on myosin-VI. The ability of calcium-calmodulin to seek out and bridge between binding site components directs a major rearrangement of the motor from a compact dormant state into a cargo binding primed state that is nonmotile. The lack of motility at high calcium is due to calmodulin switching to a higher affinity binding site, which leaves the original IQ-motif exposed, thereby destabilizing the lever arm. The return to low calcium can either restabilize the lever arm, required for translocating the cargo-bound motors toward the center of the cell, or refold the cargo-free motors into an inactive state ready for the next cellular calcium flux.

scholarly journals Oncomodulin Is Expressed Exclusively by Outer Hair Cells in the Organ of Corti

1998 ◽  
Vol 46 (1) ◽  
pp. 29-39 ◽  
Author(s):  
Nobuki Sakaguchi ◽  
Michael T. Henzl ◽  
Isolde Thalmann ◽  
Ruediger Thalmann ◽  
Bradley A. Schulte
Keyword(s):  
Hair Cells ◽  
Calcium Binding ◽  
Organ Of Corti ◽  
Ultrastructural Level ◽  
Outer Hair Cells ◽  
Regulatory Function ◽  
Electron Microscopic ◽  
Wide Range ◽  
Intracellular Organelles ◽  
Functional Relevance

Oncomodulin (OM) is a small, acidic calcium-binding protein first discovered in a rat hepatoma and later found in placental cytotrophoblasts, the pre-implantation embryo, and in a wide variety of neoplastic tissues. OM was considered to be exclusively an oncofetal protein until its recent detection in extracts of the adult guinea pig's organ of Corti. Here we report that light and electron microscopic immunostaining of gerbil, rat, and mouse inner ears with a monoclonal antibody against recombinant rat OM localizes the protein exclusively in cochlear outer hair cells (OHCs). At the ultrastructural level, high gold labeling density was seen overlying the nucleus, cytoplasm, and the cuticular plate of gerbil OHCs. Few, if any, gold particles were present over intracellular organelles and the stereocilia. Staining of a wide range of similarly processed gerbil organs failed to detect immunoreactive OM in any other adult tissues. The mammalian genome encodes one α- and one β-isoform of parvalbumin (PV). The widely distributed α PV exhibits a very high affinity for Ca2+ and is believed to serve as a Ca2+ buffer. By contrast, OM, the mammalian β PV, displays a highly attenuated affinity for Ca2+, consistent with a Ca2+-dependent regulatory function. The exclusive association of OM with cochlear OHCs in mature tissues is likely to have functional relevance. Teleological considerations favor its involvement in regulating some aspect of OHC electromotility. Although the fast electromotile response of OHCs does not require Ca2+, its gain and magnitude are modulated by efferent innervation. Therefore, OM may be involved in mediation of intracellular responses to cholinergic stimulation, which are known to be Ca2+ regulated.

scholarly journals Membrane-induced Lever Arm Expansion Allows Myosin VI to Walk with Large and Variable Step Sizes

2012 ◽  
Vol 287 (42) ◽  
pp. 35021-35035 ◽  
Author(s):  
Cong Yu ◽  
Jizhong Lou ◽  
Jingjing Wu ◽  
Lifeng Pan ◽  
Wei Feng ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Lipid Membranes ◽  
Lipid Membrane ◽  
Coiled Coil ◽  
Myosin Vi ◽  
Iq Motif ◽  
Helix Bundle ◽  
Lever Arm ◽  
Variable Step ◽  
Dynamics Simulations

Myosin VI, the only known minus-ended actin filament-dependent motor, plays diverse cellular roles both as a processive motor and as a mechanical anchor. Although myosin VI has a short lever arm containing only one “IQ-motif” and a unique insertion for CaM binding, the motor walks with large and variable step sizes of ∼30–36 nm. Here, we show that the previously predicted coiled-coil domain immediately following the IQ-motifs (referred to as the lever arm extension (LAE)) adopts a stable monomeric, three-helix bundle fold in solution. Importantly, the LAE can undergo reversible, lipid membrane-dependent conformational changes. Upon exposure to lipid membranes, the LAE adopts a partially extended rod shape, and the removal of lipids from the LAE converts it back into the compact helix bundle structure. Molecular dynamics simulations indicate that lipid membrane binding may initiate unfolding and thereby trigger the LAE expansion. This reversible, lipid membrane-dependent expansion of the LAE provides a mechanistic base for myosin VI to walk with large and variable step sizes.

Mucosal calcium uptake by rat cecum: identity with transcellular calcium absorption

1983 ◽  
Vol 244 (6) ◽  
pp. G618-G622
Author(s):  
H. N. Nellans ◽  
R. S. Goldsmith
Keyword(s):  
Calcium Binding ◽  
Calcium Uptake ◽  
Calcium Absorption ◽  
Calcium Influx ◽  
Maximal Velocity ◽  
Similar Reduction ◽  
High Calcium ◽  
Wide Range ◽  
Rat Cecum

Unidirectional intestinal calcium uptake (JCame) at the mucosal surface of rat cecum was investigated in vitro with intact tissue. Uptake is linear for 2–3 min with no indication of rapid calcium binding. Kinetic parameters reveal a maximal velocity of 333 nmol . cm-2 . h-1 with a half-maximal concentration of 0.98 mM. High-calcium diet decreased JCame by more than 60% with respect to both control and low-calcium diets; 1 mM N-ethylmaleimide caused a similar reduction. The activation energy of JCame is significantly less than that of transepithelial mucosal-to-serosal calcium absorption. Mucosal uptake was compared with transepithelial calcium fluxes in rat cecum and revealed a 1:1 correlation over a wide range of transport rates. These results are interpreted to implicate a feedback control system between basolateral calcium efflux and brush-border calcium influx.

A Color Coded STEM/SEM Image Storage System

1981 ◽  
Vol 39 ◽  
pp. 272-273
Author(s):  
Y. Kokubo ◽  
W. H. Hardy ◽  
J. Dance ◽  
K. Jones
Keyword(s):  
Image Processing ◽  
Electron Beam ◽  
Storage System ◽  
Particle Analysis ◽  
Specific Information ◽  
X Rays ◽  
Sem Image ◽  
Backscattered Electrons ◽  
Wide Range ◽  
Scanning Electron

A color coded digital image processing is accomplished by using JEM100CX TEM SCAN and ORTEC’s LSI-11 computer based multi-channel analyzer (EEDS-II-System III) for image analysis and display. Color coding of the recorded image enables enhanced visualization of the image using mathematical techniques such as compression, gray scale expansion, gamma-processing, filtering, etc., without subjecting the sample to further electron beam irradiation once images have been stored in the memory.The powerful combination between a scanning electron microscope and computer is starting to be widely used 1) - 4) for the purpose of image processing and particle analysis. Especially, in scanning electron microscopy it is possible to get all information resulting from the interactions between the electron beam and specimen materials, by using different detectors for signals such as secondary electron, backscattered electrons, elastic scattered electrons, inelastic scattered electrons, un-scattered electrons, X-rays, etc., each of which contains specific information arising from their physical origin, study of a wide range of effects becomes possible.

Changes in the secondary structures and zeta potential of soybean peptide and its calcium complexes in cell membrane medium

2021 ◽  
Author(s):  
He Liu ◽  
Ying Lv ◽  
Jingting Xu ◽  
Chen Chen ◽  
Shuntang Guo
Keyword(s):  
Enzymatic Hydrolysis ◽  
Cell Membrane ◽  
Zeta Potential ◽  
Calcium Binding ◽  
Binding Capacity ◽  
Secondary Structures ◽  
High Calcium ◽  
Calcium Complexes

In this study, soybean peptides (10-30kDa) with high calcium binding capacity were prepared by enzymatic hydrolysis and ultrafiltration. The results of cell experiments showed that the peptide could transport calcium...

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