Actin function

The role of tyrosine kinase signaling in actin cytoskeleton regulation is well established (166-171), and certain steps in the activation pathways of both Rac 1 and RhoA, two molecules known to modulate actin function, may also require tyrosine kinase activity (172,173). In fact, two recent reports have also indicated... 

ADP-ribosylation of Skeletal Muscle a-Actin to Study Actin Functions... 

Chen, X., D. S. Sullivan, and T. C. Huffaker (1994). Two yeast genes with similarity to TCP-1 are required for microtubule and actin function in vivo. Proc. Natl. Acad. Sci. USA 91, 9111-9115. 

It is Hkely that Ca + plays a role in controlhng tip growth via actin in a number of Averse fungi. This is not only due to the fact that actin and Ca + are abundant in growing tips Ca + ions are also known to regulate actin function in a number of ways. The subject has been extensively reviewed previously [31]. 

Bohl, M., Tietze, S., SokoU, A. et al. (2007). Flavonoids affect actin functions in cytoplasm and nucleus. Biophysical Journal, 93, 2767-2780. 

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.

Proteins can be broadly classified into fibrous and globular. Many fibrous proteins serve a stmctural role (11). CC-Keratin has been described. Fibroin, the primary protein in silk, has -sheets packed one on top of another. CoUagen, found in connective tissue, has a triple-hehcal stmcture. Other fibrous proteins have a motile function. Skeletal muscle fibers are made up of thick filaments consisting of the protein myosin, and thin filaments consisting of actin, troponin, and tropomyosin. Muscle contraction is achieved when these filaments sHde past each other. Microtubules and flagellin are proteins responsible for the motion of ciUa and bacterial dageUa. 

In Drosophila, Fat functions as a tumor suppressor gene and dachsous is involved in thorax, leg, and wing development. Several human and mouse homologs have been identified. FAT1 regulates actin filaments, and the Fail knockout leads to defects in glomerular slit formation [3]. 

Several agents affect the turnover of F-actin. They are not used therapeutically but serve as experimental tools to study the role of F-actin in cell function. 

The three selectins are related both structurally and functionally. They are transmembrane proteins, with an N-terminal C-type actin domain, followed by an EGF repeat and a variable number of complement control protein (CCP) domains. Selectins bind carbohydrates, which are present in various glycoproteins. 

The cytoskeleton also contains different accessory proteins, which, in accordance with their affinities and functions, are designated as microtubule-associated proteins (MAPs), actin-binding proteins (ABPs), intermediate-filament-associated proteins (IFAPs), and myosin-binding proteins. This chapter is focused on those parts of the cytoskeleton that are composed of microfilaments and microtubules and their associated proteins. The subject of intermediate filaments is dealt with in detail in Volume 2. 

More than 50 proteins have been discovered in the cytosol of nonmuscle cells that bind to actin and affect the assembly and disassembly of actin filaments or the cross-linking of actin filaments with each other, with other filamentous components of the cytoskeleton, or with the plasma membrane. Collectively, these are known as actin-binding proteins (ABPs). Their mechanisms of actions are complex and are subject to regulation by specific binding affinities to actin and other molecules, cooperation or competition with other ABPs, local changes in the concentrations of ions in the cytosol, and physical forces (Way and Weeds, 1990). Classifications of ABPs have been proposed that are based on their site of binding to actin and on their molecular structure and function (Pollard and Cooper, 1986 Herrmann, 1989 Pollard et al., 1994). These include the following ... 

Proteins that bind to actin monomers and inhibit polymerization are designated as profilins (12—15 kD) (Sun et al., 1995). In addition to functioning as an actin-monomer-sequestering protein, profilin binds at least three other... 

Thus far, microtubules and actin filaments and their associated proteins have been discussed to advantage as independent cytoskeletal components. In actual fact, all of the components of the cytoskeleton (including intermediate filaments) are precisely integrated with one another (Langford, 1995), as well as with various cytoplasmic organelles, the nuclear membrane, the plasma membrane, and the extracellular matrix. In its totality the cytoskeleton subserves many coordinated and regulated functions in the cell ... 

The membrane cytoskeleton (inclusive of the submembranous actin-spec-trin network) may function in the establishment and maintenance of restricted domains of specific proteins on the plasma membrane of polarized epithelial cells (Rodriguez-Boulan and Nelson, 1989 Mays et al., 1994). 

Pollard, T.D. Cooper, J.R. (1986). Actin and actin-binding proteins. A critical evaluation of mechanisms and functions. Ann. Rev. Biochem. 55, 987-1035. 

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