The long term goal of this work is to understand the molecular basis for the regulation of Arp2/3 complex. Arp2/3 complex is an essential component of the actin assembly machinery because of its ability to nucleate branched actin filaments in response to cellular signals. Arp2/3 complex is involved in a number of processes that occur in healthy cells, such as endocytosis and motility of growth cones, but also plays roles in host cell infection by bacterial pathogens and the metastasis of tumor cells. The activity of Arp2/3 complex is tightly regulated in vivo, and numerous activators and inhibitors of the complex have been discovered, including WASp/Scar family proteins and coronin family proteins. Despite the central importance of the Arp2/3 complex, the molecular mechanism of its activation is still unknown due to the lack of biochemical and high resolution structural information of partially or fully activated states of the complex. Here we propose to use structural, biochemical and cell biological approaches to determine a precise molecular mechanism by which Arp2/3 complex and its regulatory proteins create branched actin networks. We will pursue this goal through the following three specific aims: 1.) Determine the key structural elements that allow Arp2/3 complex to bind to mother and daughter filaments of actin;2.) Determine how WASp/Scar family proteins activate Arp2/3 complex;and 3.) Determine how Coronin proteins inhibit Arp2/3 complex. Our approach will be to use mutational analysis and biochemical assays to precisely map the interactions of S. pombe Arp2/3 complex with mother and daughter filaments of actin. We will use mass spectrometry, x-ray crystallography and mutational analysis to determine where WASp/Scar family proteins bind to Arp2/3 complex and how they recruit the first actin monomer for the daughter filament. Finally, we will use biochemical and structural methods to determine how yeast coronin proteins inhibit Arp2/3 complex and influence its interactions with actin filaments.

Public Health Relevance

In this work, we are studying at the molecular level cellular machinery that controls actin polymerization. Bacteria and viruses use this machinery to infect human cells and cancerous cells depend on it to spread. Therefore, improving our understanding of the molecules that constitute this machinery will contribute to our understanding of diseased states in humans and how to treat them.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Nuclear and Cytoplasmic Structure/Function and Dynamics Study Section (NCSD)
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Gindhart, Joseph G
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University of Oregon
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Luan, Qing; Liu, Su-Ling; Helgeson, Luke A et al. (2018) Structure of the nucleation-promoting factor SPIN90 bound to the actin filament nucleator Arp2/3 complex. EMBO J 37:
Balzer, Connor J; Wagner, Andrew R; Helgeson, Luke A et al. (2018) Dip1 Co-opts Features of Branching Nucleation to Create Linear Actin Filaments that Activate WASP-Bound Arp2/3 Complex. Curr Biol 28:3886-3891.e4
Luan, Qing; Zelter, Alex; MacCoss, Michael J et al. (2018) Identification of Wiskott-Aldrich syndrome protein (WASP) binding sites on the branched actin filament nucleator Arp2/3 complex. Proc Natl Acad Sci U S A 115:E1409-E1418
Rodnick-Smith, Max; Liu, Su-Ling; Balzer, Connor J et al. (2016) Identification of an ATP-controlled allosteric switch that controls actin filament nucleation by Arp2/3 complex. Nat Commun 7:12226
Rodnick-Smith, Max; Luan, Qing; Liu, Su-Ling et al. (2016) Role and structural mechanism of WASP-triggered conformational changes in branched actin filament nucleation by Arp2/3 complex. Proc Natl Acad Sci U S A 113:E3834-43
Helgeson, Luke A; Prendergast, Julianna G; Wagner, Andrew R et al. (2014) Interactions with actin monomers, actin filaments, and Arp2/3 complex define the roles of WASP family proteins and cortactin in coordinately regulating branched actin networks. J Biol Chem 289:28856-69
Luan, Qing; Nolen, Brad J (2013) Structural basis for regulation of Arp2/3 complex by GMF. Nat Struct Mol Biol 20:1062-8
Liu, Su-Ling; May, Jordan R; Helgeson, Luke A et al. (2013) Insertions within the actin core of actin-related protein 3 (Arp3) modulate branching nucleation by Arp2/3 complex. J Biol Chem 288:487-97
Wagner, Andrew R; Luan, Qing; Liu, Su-Ling et al. (2013) Dip1 defines a class of Arp2/3 complex activators that function without preformed actin filaments. Curr Biol 23:1990-8
Helgeson, Luke A; Nolen, Brad J (2013) Mechanism of synergistic activation of Arp2/3 complex by cortactin and N-WASP. Elife 2:e00884

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