ATPase-like domain of the ASKHA (Acetate and Sugar Kinases/Hsc70/Actin) superfamily; The ASKHA superfamily, also known as actin-like ATPase domain superfamily, includes acetate and sugar kinases, heat-shock cognate 70 (Hsp70) and actin family proteins. They either function as conformational hydrolases (e.g. Hsp70, actin) that perform simple ATP hydrolysis, or as metabolite kinases (e.g. glycerol kinase) that catalyze the transfer of a phosphoryl group from ATP to their cognate substrates. Both activities depend on the presence of specific metal cations. ASKHA superfamily members share a common core fold that includes an actin-like ATPase domain consisting of two subdomains (denoted I _ II) with highly similar ribonuclease (RNase) H-like folds. The fold of each subdomain is characterized by a central five strand beta-sheet and flanking alpha-helices. The two subdomains form an active site cleft in which ATP binds at the bottom. Another common feature of ASKHA superfamily members is the coupling of phosphoryl-group transfer to conformational rearrangement, leading to domain closure. Substrate binding triggers protein motion.

                         10
                 ....*....|.
gi 565055047   1 LFQPSFLGMES 11
Cdd:cd10224  256 LFQPSFLGMEA 266

nucleotide-binding domain (NBD) of actin and similar proteins; Actin is a ubiquitous protein involved in the formation of filaments that are major components of the cytoskeleton. It is a highly dynamic structural protein network involved in processes such as cell contraction, cell motility, vesicle trafficking, intracellular organization, cytokinesis, endocytosis and apoptosis. Actin is a monomeric globular protein (G-actin) that reversibly polymerizes to form filaments (F-actin). Each actin protomer binds one molecule of ATP and either calcium or magnesium ions. At low salt concentrations, actin exists as a monomer, and as the salt concentration rises F-actin forms, with the consequent hydrolysis of ATP. F-actin assembly is in constant flux with G-actin association occurring at the barbed end (+) and its disassociation at the pointed end (-). Actin monomers that have been released from the pointed end can be reused, if the ADP is exchanged for ATP. F-actin filaments can assemble into higher order structures, for example branched F-actin, and stress fibers. Actin binding proteins regulate actin filament dynamics by a range of functions including actin severing, depolymerizing, capping, stabilizing and de novo actin polymerization. Actins interaction with myosin is the basis of muscular contraction and many aspects of cell motility. In vertebrates there are three main groups of actin isoforms, alpha, beta and gamma. The alpha actins found in muscle tissues are a major constituent of the contractile apparatus. The beta and gamma actins co-exist in most cell types as components of the cytoskeleton and as mediators of internal cell motility. In plants there are many isoforms which are probably involved in a variety of functions such as cytoplasmic streaming, cell shape determination, tip growth, graviperception, cell wall deposition, etc.

                         10
                 ....*....|.
gi 565055047   1 LFQPSFLGMES 11
Cdd:cd10224  256 LFQPSFLGMEA 266

nucleotide-binding domain (NBD) of actin and similar proteins; Actin is a ubiquitous protein involved in the formation of filaments that are major components of the cytoskeleton. It is a highly dynamic structural protein network involved in processes such as cell contraction, cell motility, vesicle trafficking, intracellular organization, cytokinesis, endocytosis and apoptosis. Actin is a monomeric globular protein (G-actin) that reversibly polymerizes to form filaments (F-actin). Each actin protomer binds one molecule of ATP and either calcium or magnesium ions. At low salt concentrations, actin exists as a monomer, and as the salt concentration rises F-actin forms, with the consequent hydrolysis of ATP. F-actin assembly is in constant flux with G-actin association occurring at the barbed end (+) and its disassociation at the pointed end (-). Actin monomers that have been released from the pointed end can be reused, if the ADP is exchanged for ATP. F-actin filaments can assemble into higher order structures, for example branched F-actin, and stress fibers. Actin binding proteins regulate actin filament dynamics by a range of functions including actin severing, depolymerizing, capping, stabilizing and de novo actin polymerization. Actins interaction with myosin is the basis of muscular contraction and many aspects of cell motility. In vertebrates there are three main groups of actin isoforms, alpha, beta and gamma. The alpha actins found in muscle tissues are a major constituent of the contractile apparatus. The beta and gamma actins co-exist in most cell types as components of the cytoskeleton and as mediators of internal cell motility. In plants there are many isoforms which are probably involved in a variety of functions such as cytoplasmic streaming, cell shape determination, tip growth, graviperception, cell wall deposition, etc.

                         10
                 ....*....|.
gi 565055047   1 LFQPSFLGMES 11
Cdd:cd10224  256 LFQPSFLGMEA 266