In cytoskeleton

Monomeric actin binds ATP very tightly with an association constant Ka of 1 O M in low ionic strength buffers in the presence of Ca ions. A polymerization cycle involves addition of the ATP-monomer to the polymer end, hydrolysis of ATP on the incorporated subunit, liberation of Pi in solution, and dissociation of the ADP-monomer. Exchange of ATP for bound ADP occurs on the monomer only, and precedes its involvement in another polymerization cycle. Therefore, monomer-polymer exchange reactions are linked to the expenditure of energy exactly one mol of ATP per mol of actin is incorporated into actin filaments. As a result, up to 40% of the ATP consumed in motile cells is used to maintain the dynamic state of actin. Thus, it is important to understand how the free energy of nucleotide hydrolysis is utilized in cytoskeleton assembly. 

Valouev lA, Kushnirov VV, Ter-Avanesyan MD (2002) Yeast polypeptide chain release factors eREl and eRE3 are involved in cytoskeleton organization and cell cycle regulation. Cell Motil Cytoskelet 52 161-... 

Wiche, G. (1998). Role of plectin in cytoskeleton organization and dynamics./. Cell Sci. Ill, 2477-2486. 

Bourguignon, L. Y. W., Gunja-Smith, Z., Bda, N., Zhu, H. B., Young, L. J. T, Muller, W. J. and Cardiff, R. D. (1998). CD44v3,8-10 is involved in cytoskeleton-mediated tumor cell migration and matrix metalloproteinase (MMP-9). association in metastatic breast cancer cells. J. Cell Physiol. 59176, 206-215. 

Biliary epithelial cells are organ-typical. They constitute some 3.5% of all hepatic cells. Depending on the size of the biliary ducts in which they are located, they show distinct histological and histochemical variations. In comparison with hepatocytes, biliary epithelial cells contain fewer mitochondria and less ER there is a complete absence of cytochrome P 450. They are rich in cytoskeleton and contain Golgi apparatus and vesicles. The round-to-oval nuclei lie in the basal cytoplasm. These biliary cells probably play a role in biligenesis. (63) The epithelial cells of the intermediate ductules are also regarded as stem cells for the liver parenchyma. 

Filamin 95557 Insulin causes changes in cytoskeleton, flilamin A may interact with insulin receptor [32]... 

R. O. Hynes, Relationship Between Fibronectin and the Cytoskeleton, in Cytoskeleton Elements and Plasma Membrane Organisation, Elsevier/North-Holland, Amsterdam (1981), p. 100. 

Dalby, M.J., Childs, S., Riehle, M.O., Johnstone, H.J.H., Affiossman, S., Curtis, A.S.G. Fibroblast reaction to island topography changes in cytoskeleton and morphology with time. Biomaterials 24,927-935 (2003)... 

The modem era of biochemistry and molecular biology has been shaped not least by the isolation and characterization of individual molecules. Recently, however, more and more polyfunctional macromolecular complexes are being discovered, including nonrandomly codistributed membrane-bound proteins [41], These are made up of several individual proteins, which can assemble spontaneously, possibly in the presence of a lipid membrane or an element of the cytoskeleton [42] which are themselves supramolecular complexes. Some of these complexes, e.g. snail haemocyanin [4o], are merely assembled from a very large number of identical subunits vimses are much larger and more elaborate and we are still some way from understanding the processes controlling the assembly of the wonderfully intricate and beautiful stmctures responsible for the iridescent colours of butterflies and moths [44]. 

Fig. 1. The GP Ib-IX-V complex. The complex consists of seven transmembrane polypeptides denoted GP Iba (mol wt 145,000), GP IbP (mol wt 24,000), GPIX (mol wt 17,000) and GP V (mol wt 82,000), in a stoichiometry of 2 2 2 1. The hatched region represents the plasma membrane. The area above the hatched region represents the extracellular space that below represents the cytoplasm. The complex is a major attachment site between the plasma membrane and the cytoskeleton. Two molecules associated with the cytoplasmic domain are depicted a 14-3-3 dimer, which may mediate intracellular signaling, and actin-binding protein, which connects the complex to the cortical cytoskeleton and fixes its position and influences its function.

Microfilaments and Microtubules. There are two important classes of fibers found in the cytoplasm of many plant and animal ceUs that are characterized by nematic-like organization. These are the microfilaments and microtubules which play a central role in the determination of ceU shape, either as the dynamic element in the contractile mechanism or as the basic cytoskeleton. Microfilaments are proteinaceous bundles having diameters of 6—10 nm that are chemically similar to actin and myosin muscle ceUs. Microtubules also are formed from globular elements, but consist of hoUow tubes that are about 30 nm in diameter, uniform, and highly rigid. Both of these assemblages are found beneath the ceU membrane in a linear organization that is similar to the nematic Hquid crystal stmcture. 

In this lecture we will be concerned by exocytosis of neurotransmitters by chromaffin cells. These cells, located above kidneys, produce the adrenaline burst which induces fast body reactions they are used in neurosciences as standard models for the study of exocytosis by catecholaminergic neurons. Prior to exocytosis, adrenaline is contained at highly concentrated solutions into a polyelectrolyte gel matrix packed into small vesicles present in the cell cytoplasm and brought by the cytoskeleton near the cell outer membrane. Stimulation of the cell by divalent ions induces the fusion of the vesicles membrane with that of the cell and hence the release of the intravesicular content into the outer-cytoplasmic region. 

Just how fast can proteins move in a biological membrane Many membrane proteins can move laterally across a membrane at a rate of a few microns per minute. On the other hand, some integral membrane proteins are much more restricted in their lateral movement, with diffusion rates of about 10 nm/sec or even slower. These latter proteins are often found to be anchored to the cytoskeleton (Chapter 17), a complex latticelike structure that maintains the cell s shape and assists in the controlled movement of various substances through the ceil. 

The cytoplasmic domains of protocadherins are unrelated to those of classical cadherins. They do not bind catenins and it is not clear whether they are associated with the cytoskeleton [1]. Some protocadherins interact with the c- src-related kinase Fyn, indicating a role in signal transduction (see below). 

The calpain system has a number of different roles in cells, including remodeling of cytoskeleton attachments... 

Interactions with the cytoskeleton seem to be responsible for the processing and the targeting of the Na+/fC+-ATPase to the appropriate compartment structures. Protein kinases are considered to play an essential role in modulation of the sodium pump. 

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