Mammalian actin-related protein 2/3 complex localizes to regions of lamellipodial protrusion and is composed of evolutionarily conserved proteins.
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ABSTRACT:
SUBMITTER: Machesky LM
PROVIDER: S-EPMC1218893 | biostudies-other | 1997 Nov
REPOSITORIES: biostudies-other
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Project description:The Arp2/3 protein complex has been implicated in the control of actin polymerization in cells. The human complex consists of seven subunits which include the actin related proteins Arp2 and Arp3, and five others referred to as p41-Arc, p34-Arc, p21-Arc, p20-Arc, and p16-Arc (p omplex). We have determined the predicted amino acid sequence of all seven subunits. Each has homologues in diverse eukaryotes, implying that the structure and function of the complex has been conserved through evolution. Human Arp2 and Arp3 are very similar to family members from other species. p41-Arc is a new member of the Sop2 family of WD (tryptophan and aspartate) repeat-containing proteins and may be posttranslationally modified, suggesting that it may be involved in regulating the activity and/or localization of the complex. p34-Arc, p21-Arc, p20-Arc, and p16-Arc define novel protein families. We sought to evaluate the function of the Arp2/3 complex in cells by determining its intracellular distribution. Arp3, p34-Arc, and p21-Arc were localized to the lamellipodia of stationary and locomoting fibroblasts, as well to Listeria monocytogenes assembled actin tails. They were not detected in cellular bundles of actin filaments. Taken together with the ability of the Arp2/3 complex to induce actin polymerization, these observations suggest that the complex promotes actin assembly in lamellipodia and may participate in lamellipodial protrusion.
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Project description:The dynein activator dynactin is a multiprotein complex with distinct microtubule- and cargo-binding domains. The cargo-binding domain contains a short, actin-like filament of the actin-related protein Arp1, a second actin-related protein, Arp11, and conventional actin. The length of this filament is invariant in dynactin isolated from multiple species and tissues, suggesting that activities that regulate Arp1 polymerization are important for dynactin assembly. Arp11 is present in a protein complex localized at the pointed end of the Arp1 minifilament, whereas actin capping protein (CapZ) is present at the barbed end. Either might cooperate with conventional actin to cap Arp1. We tested the ability of Arp11 to interact with conventional actin and found it could coassemble. Like Arp1, cytosolic Arp11 is found only in dynactin, suggesting that Arp11 and free cytosolic actin do not interact significantly. Recombinant Arp11 and Arp1 were demonstrated to interact by coprecipitation. We developed an in vivo assay for Arp11-Arp1 interaction based on previous observations that Arp1 forms filamentous assemblies when overexpressed in cultured cells. Arp11 significantly decreases the formation of these organized Arp1 assemblies. Finally, this assay was used to confirm the identity of a putative Arp11 homolog in Drosophila melanogaster.
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