The long-term goal is to understand the structural and functional mechanisms that control actin cytoskeleton dynamics in health and disease. Malfunction of cytoskeletal components is linked to many diseases, and several bacterial pathogens hijack the cytoskeleton for infection. Here, the focus will be on actin filament nucleation, which determines the time and location for actin polymerization.
Aim 1 will address the molecular mechanism for nucleation, branch formation and debranching by Arp2/3 complex. Arp2/3 complex is activated by nucleation promoting factors (NPFs). Two NPFs are needed for optimal activation. One of the NPFs interacts with subunit ArpC1 of Arp2/3 complex. We will characterize this interaction at the structural and functional levels. New data suggests that interaction of Arp2/3 complex with NPFs promotes binding to the side of the mother filament to form a branch. We will test the role of pre-association of NPFs with actin for binding to the mother filament. In cells, older branches are disassembled by GMF. We will characterize the mechanism of debranching of mammalian Arp2/3 complex by GMF using TIRF microscopy, and establish the role of GMF phosphorylation for this activity.
In Aim 2 will address the molecular mechanism for filament nucleation by Lmod, a muscle-specific nucleator discovered in our lab. We previously characterized the skeletal/cardiac isoform Lmod2. The smooth muscle isoform Lmod1 shares only 37% sequence identity with Lmod2, and is 105-aa longer, which translates into substantial functional differences between the two isoforms. We will investigate the two isoforms in parallel, to understand the structural and functional bases for their muscle-type specific activities.
Aim 3 will address the molecular mechanism for filament nucleation and elongation by Rickettsia Sca2. Sca2 is the only bacterial protein known to promote both, actin nucleation and elongation, mimicking eukaryotic formins to assemble actin comet tails for Rickettsia motility and virulence. We recently discovered that Sca2's functional mimicry of formins is achieved through a novel molecular mechanism. Here we will investigate how the interaction of the N- and C-terminal domains of Sca2 leads to actin nucleation and elongation within a monomeric protein.

Public Health Relevance

This project addresses a major lack of understanding of the mechanisms controlling actin cytoskeleton dynamics in health and disease. A better understanding of these processes, and specifically actin filament nucleation, has both fundamental importance and direct relevance to human health, since malfunctioning of cytoskeletal proteins is the direct cause of many diseases, including cancer metastasis, neurodegenerative disorders and defective immune response.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM073791-12
Application #
9059108
Study Section
Macromolecular Structure and Function C Study Section (MSFC)
Program Officer
Gindhart, Joseph G
Project Start
2005-04-01
Project End
2018-04-30
Budget Start
2016-05-01
Budget End
2017-04-30
Support Year
12
Fiscal Year
2016
Total Cost
Indirect Cost
Name
University of Pennsylvania
Department
Physiology
Type
Schools of Medicine
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
Mentes, Ahmet; Huehn, Andrew; Liu, Xueqi et al. (2018) High-resolution cryo-EM structures of actin-bound myosin states reveal the mechanism of myosin force sensing. Proc Natl Acad Sci U S A 115:1292-1297
Turegun, Bengi; Baker, Richard W; Leschziner, Andres E et al. (2018) Actin-related proteins regulate the RSC chromatin remodeler by weakening intramolecular interactions of the Sth1 ATPase. Commun Biol 1:
Drazic, Adrian; Aksnes, Henriette; Marie, Michaƫl et al. (2018) NAA80 is actin's N-terminal acetyltransferase and regulates cytoskeleton assembly and cell motility. Proc Natl Acad Sci U S A 115:4399-4404
Arnesen, Thomas; Marmorstein, Ronen; Dominguez, Roberto (2018) Actin's N-terminal acetyltransferase uncovered. Cytoskeleton (Hoboken) 75:318-322
Lee, In-Gyun; Olenick, Mara A; Boczkowska, Malgorzata et al. (2018) A conserved interaction of the dynein light intermediate chain with dynein-dynactin effectors necessary for processivity. Nat Commun 9:986
Burke, Thomas A; Harker, Alyssa J; Dominguez, Roberto et al. (2017) The bacterial virulence factors VopL and VopF nucleate actin from the pointed end. J Cell Biol 216:1267-1276
Boczkowska, Malgorzata; Yurtsever, Zeynep; Rebowski, Grzegorz et al. (2017) Crystal Structure of Leiomodin 2 in Complex with Actin: A Structural and Functional Reexamination. Biophys J 113:889-899
Fowler, Velia M; Dominguez, Roberto (2017) Tropomodulins and Leiomodins: Actin Pointed End Caps and Nucleators in Muscles. Biophys J 112:1742-1760
Dominguez, Roberto (2016) The WH2 Domain and Actin Nucleation: Necessary but Insufficient. Trends Biochem Sci 41:478-490
Boczkowska, Malgorzata; Rebowski, Grzegorz; Kremneva, Elena et al. (2015) How Leiomodin and Tropomodulin use a common fold for different actin assembly functions. Nat Commun 6:8314

Showing the most recent 10 out of 41 publications