This site features trending Actin-linked items from the web for 5 of August 2019.
Trending Actin news item:
Scientists show actin in action Actin is the second most abundant protein on earth, and scientists have extensively detailed the chemistry that enables it to string together into filaments that support the structures for muscle contraction and other cell movements. However, some questions have perplexed researchers for decades, such as why one end of the filament grows so much faster than the other end and how actin, once assembled into filaments, interacts with energy-storing molecule ATP. Yale scientists Steve Chou and Tom Pollard used advanced cryo-microscopy to determine the highest resolution structures of actin filaments, which answered these and other questions… read the entire news item (from YaleNews)
Featured recent scientific publication on Actin:
Stoichiometry controls activity of phase-separated clusters of actin signaling proteins Biomolecular condensates concentrate macromolecules into foci without a surrounding membrane. Many condensates appear to form through multivalent interactions that drive liquid-liquid phase separation (LLPS). LLPS increases the specific activity of actin regulatory proteins toward actin assembly by the Arp2/3 complex. We show that this increase occurs because LLPS of the Nephrin–Nck–N-WASP signaling pathway on lipid bilayers increases membrane dwell time of N-WASP and Arp2/3 complex, consequently increasing actin assembly. Dwell time varies with relative stoichiometry of the signaling proteins in the phase-separated clusters, rendering N-WASP and Arp2/3 activity stoichiometry dependent. This mechanism of controlling protein activity is enabled by the stoichiometrically undefined nature of biomolecular condensates. Such regulation should be a general feature of signaling systems that assemble through multivalent interactions and drive nonequilibrium outputs… read the entire scientific publication (from Science)
Trending tweet on #Actin:
Background knowledge on Actin:
Actin Assembly/Disassembly Actin is a monomeric protein that polymerizes into helical filaments. Apart from its role in muscle cells as a scaffold for myosin-based contraction, actin’s function often depends on its ability to assemble into filaments from monomers rapidly, and to disassemble equally rapidly. Actin alone can polymerize in vitro, but both the kinetics and equilibria of polymerization are controlled in cells by specific actin-binding proteins that serve to modify the assembly/disassembly cycle inherent to actin itself. Some actin-binding proteins of particular importance are sequestering proteins, profilin, capping protein, and ADF/cofilin. Actin Structure, ACTIN MONOMER STRUCTURES: Actin is a 43 kDa (375 amino acid) globular monomer, which binds a nucleotide (ATP or ADP in cells) in a deep cleft between two halves of the protein (Figure 1A). The affinity of actin for nucleotide is greatly increased by divalent cation. Due to its relative cytosolic abundance (100s of mM), Mg2þ is the main actin-bound divalent cation in cells, but other cations, especially Ca2þ, are used for special purposes in vitro. ACTIN ISOFORMS AND MODEL SYSTEMS: Mammals contain six highly conserved actin isoforms, with at least 93% amino acid identity (Table I). Actin from non-mammals is similarly conserved, with budding yeast 88% and Acanthamoeba castellani 95% identical to human non-muscle b-actin. Bacteria contain several proteins with some properties similar to actin, Mbl, and Mreb. Much of the biochemical data on actin assembly/ disassembly is derived from studies of vertebrate muscle actin. Seminal studies on actin biochemistry were begun by Straub and Feuer during World War II using rabbit muscle actin. The sole actin isoform of budding yeast has also been a model, due to the combination of biochemistry and genetics in this system. The highly similar sequences of actins from diverse species suggest that results in these model systems will be close approximations for most actins. However, specific biochemical properties can vary between actins, such as affinities for some actin-binding proteins. Individual cells can possess multiple actin isoforms simultaneously. Mammalian non-muscle cells often contain both b- and g-actin. The reasons behind this diversity are not well understood, but differential subcellular localization has been observed. Some unicellular organisms possess multiple actin isoforms. For instance, Dictyostelium has 20 actin genes… read more (from Encyclopedia of Biological Chemistry, 1st Edition)
Keywords: Actin, #Actin, Dictyostelium, b- and g-actin, profilin, capping protein, ADF/cofilin, filaments.
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