# Structure-function study of Arp2/3 complex and a novel role for actin branching

> **NIH NIH F31** · UNIVERSITY OF PENNSYLVANIA · 2020 · $30,599

## Abstract

Project Summary/Abstract:
The long-term goal of this proposal is to understand the structural and functional mechanisms that control
actin cytoskeleton dynamics in health and disease. Specifically, Aim-1 will tackle the long-standing problem of
how WASP-family Nucleation Promoting Factors interact with and activate actin branch formation by the
Arp2/3 complex. Because nucleation is the rate-limiting step in actin polymerization, cells use actin nucleators
to precisely control the de novo formation of actin filaments in time and space. Among these, the Arp2/3
complex is the sole nucleator of branched actin networks. Branched actin assembly is important in myofibril
development and is misregulated in Wiskott-Aldrich Syndrome causing thrombocytopenia and platelet
dysfunction. My plans to understand the mechanism of Arp2/3 complex activation build upon the ability to
perform biochemical and structural studies on the baculovirus-expressed Arp2/3 complex and subcomplexes.
Extensive preliminary work provides the scientific premise and supports feasibility. In brief, the aims of this
proposal tackle the following questions pertaining to Arp2/3 complex's mechanism of activation: (1) In what
order do the Nucleation Promoting Factors that activate Arp2/3 complex bind and what is their molecular interaction
with the complex? (2) How does Arp2/3 complex interact with the mother filament? (3) What are the functional
consequences of these interactions? Aim 2 of this proposal focuses on Arp2/3 complex's newly appreciated role in
focal adhesion maturation. Focal adhesions are macromolecular assemblies that link the extracellular matrix to
the actin cytoskeleton. An unresolved and fundamental question in cell motility and adhesion is; how are actin
networks recruited to focal adhesions? Recently, Arp2/3 was shown to interact with Kindlin, an important
activator of focal adhesions. Based on this observation and my own preliminary results, here I dissect Arp2/3
complex's role in focal adhesion maturation, with the underlying hypothesis that Kindlin recruits Arp2/3 to
initiate the formation of dendritic actin networks at adhesion sites. Towards this aim, my proposal will answer
the following questions: (1) Does Kindlin bind free Arp2/3, branch junctions, or both? (2) Does Kindlin affect Arp2/3
nucleation activity? (3) At an atomic level, how does Kindlin bind Arp2/3? Improper focal adhesion formation is
linked to various diseases including cardiomyopathy, hematopoic dysfunction and muscular dystrophy.
Understanding Arp2/3 complex's role at focal adhesions is an important step towards understand platelet
activation, muscle development and healthy physiology as a whole.
 These two aims are thematic of the laboratory's workflow, tackling mechanistic questions in vitro with
biochemical and structural assays and subsequently understanding their functional consequences in vitro and
in vivo. Taken together, these aims will have a far reaching impact and will train me in the...

## Key facts

- **NIH application ID:** 9859202
- **Project number:** 5F31HL146077-02
- **Recipient organization:** UNIVERSITY OF PENNSYLVANIA
- **Principal Investigator:** AUSTIN ZIMMET
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $30,599
- **Award type:** 5
- **Project period:** 2019-01-01 → 2020-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9859202

## Citation

> US National Institutes of Health, RePORTER application 9859202, Structure-function study of Arp2/3 complex and a novel role for actin branching (5F31HL146077-02). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9859202. Licensed CC0.

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