Abrar Bhat

All Publications

• Mechanisms of mechanosensing by MLP and α-actinin-2 in cardiac hypertrophy Bhat, A., Vera, C., Marang, C., Giri, P., Bernstein, D., Dunn, A. CELL PRESS. 2026: 327a

  View details for Web of Science ID 001717762500141

• Contractile actin flows drive patterning of membrane components with differential actin-binding affinities Bhat, A. A., Das, A., Koester, D. V., Rao, M., Mayor, S. CELL PRESS. 2023: 263A

  View details for Web of Science ID 000989629701398

• Reconstitution of Membrane-tethered Minimal Actin Cortices on Supported Lipid Bilayers JOVE-JOURNAL OF VISUALIZED EXPERIMENTS Koster, D., Bhat, A., Talluri, S., Mayor, S. 2022

  Abstract

  The surface of a living cell provides a versatile active platform for numerous cellular processes, which arise from the interplay of the plasma membrane with the underlying actin cortex. In the past decades, reconstituted, minimal systems based on supported lipid bilayers in combination with actin filament networks have proven to be very instrumental in unraveling basic mechanisms and consequences of membrane-tethered actin networks, as well as in studying the functions of individual membrane-associated proteins. Here, we describe how to reconstitute such active composite systems in vitro that consist of fluid supported lipid bilayers coupled via membrane-associated actin-binding proteins to dynamic actin filaments and myosin motors that can be readily observed via total internal reflection fluorescence microscopy. An open-chamber design allows one to assemble the system in a step-by-step manner and to systematically control many parameters such as linker protein concentration, actin concentration, actin filament length, actin/myosin ratio, as well as ATP levels. Finally, we discuss how to control the quality of the system, how to detect and troubleshoot commonly occurring problems, and some limitations of this system in comparison with the living cell surface.

  View details for DOI 10.3791/63968

  View details for Web of Science ID 000866477300005

  View details for PubMedID 35913196

  View details for PubMedCentralID PMC7616522

• Evolutionarily related small viral fusogens hijack distinct but modular actin nucleation pathways to drive cell-cell fusion PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Chan, K., Arthur, A. L., Morstein, J., Jin, M., Bhat, A., Schlesinger, D., Son, S., Stevens, D. A., Drubin, D. G., Fletcher, D. A. 2021; 118 (1)

  Abstract

  Fusion-associated small transmembrane (FAST) proteins are a diverse family of nonstructural viral proteins. Once expressed on the plasma membrane of infected cells, they drive fusion with neighboring cells, increasing viral spread and pathogenicity. Unlike viral fusogens with tall ectodomains that pull two membranes together through conformational changes, FAST proteins have short fusogenic ectodomains that cannot bridge the intermembrane gap between neighboring cells. One orthoreovirus FAST protein, p14, has been shown to hijack the actin cytoskeleton to drive cell-cell fusion, but the actin adaptor-binding motif identified in p14 is not found in any other FAST protein. Here, we report that an evolutionarily divergent FAST protein, p22 from aquareovirus, also hijacks the actin cytoskeleton but does so through different adaptor proteins, Intersectin-1 and Cdc42, that trigger N-WASP-mediated branched actin assembly. We show that despite using different pathways, the cytoplasmic tail of p22 can replace that of p14 to create a potent chimeric fusogen, suggesting they are modular and play similar functional roles. When we directly couple p22 with the parallel filament nucleator formin instead of the branched actin nucleation promoting factor N-WASP, its ability to drive fusion is maintained, suggesting that localized mechanical pressure on the plasma membrane coupled to a membrane-disruptive ectodomain is sufficient to drive cell-cell fusion. This work points to a common biophysical strategy used by FAST proteins to push rather than pull membranes together to drive fusion, one that may be harnessed by other short fusogens responsible for physiological cell-cell fusion.

  View details for DOI 10.1073/pnas.2007526118

  View details for Web of Science ID 000607270100010

  View details for PubMedID 33443166

  View details for PubMedCentralID PMC7817207

• Stratification relieves constraints from steric hindrance in the generation of compact actomyosin asters at the membrane cortex SCIENCE ADVANCES Das, A., Bhat, A., Sknepnek, R., Koster, D., Mayor, S., Rao, M. 2020; 6 (11): eaay6093

  Abstract

  Recent in vivo studies reveal that several membrane proteins are driven to form nanoclusters by active contractile flows arising from localized dynamic patterning of F-actin and myosin at the cortex. Since myosin-II assemble as minifilaments with tens of myosin heads, one might worry that steric considerations would obstruct the emergence of nanoclustering. Using coarse-grained, agent-based simulations that account for steric constraints, we find that the patterns exhibited by actomyosin in two dimensions, do not resemble the steady-state patterns in our in vitro reconstitution of actomyosin on a supported bilayer. We perform simulations in a thin rectangular slab, separating the layer of actin filaments from myosin-II minifilaments. This recapitulates the observed features of in vitro patterning. Using super resolution microscopy, we find evidence for such stratification in our in vitro system. Our study suggests that molecular stratification may be an important organizing feature of the cortical cytoskeleton in vivo.

  View details for DOI 10.1126/sciadv.aay6093

  View details for Web of Science ID 000520866800025

  View details for PubMedID 32195346

  View details for PubMedCentralID PMC7065884

• Actomyosin dynamics drive local membrane component organization in an in vitro active composite layer PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Koester, D., Husain, K., Iljazi, E., Bhat, A., Bieling, P., Mullins, R., Rao, M., Mayor, S. 2016; 113 (12): E1645-E1654

  Abstract

  The surface of a living cell provides a platform for receptor signaling, protein sorting, transport, and endocytosis, whose regulation requires the local control of membrane organization. Previous work has revealed a role for dynamic actomyosin in membrane protein and lipid organization, suggesting that the cell surface behaves as an active composite composed of a fluid bilayer and a thin film of active actomyosin. We reconstitute an analogous system in vitro that consists of a fluid lipid bilayer coupled via membrane-associated actin-binding proteins to dynamic actin filaments and myosin motors. Upon complete consumption of ATP, this system settles into distinct phases of actin organization, namely bundled filaments, linked apolar asters, and a lattice of polar asters. These depend on actin concentration, filament length, and actin/myosin ratio. During formation of the polar aster phase, advection of the self-organizing actomyosin network drives transient clustering of actin-associated membrane components. Regeneration of ATP supports a constitutively remodeling actomyosin state, which in turn drives active fluctuations of coupled membrane components, resembling those observed at the cell surface. In a multicomponent membrane bilayer, this remodeling actomyosin layer contributes to changes in the extent and dynamics of phase-segregating domains. These results show how local membrane composition can be driven by active processes arising from actomyosin, highlighting the fundamental basis of the active composite model of the cell surface, and indicate its relevance to the study of membrane organization.

  View details for DOI 10.1073/pnas.1514030113

  View details for Web of Science ID 000372488200010

  View details for PubMedID 26929326

  View details for PubMedCentralID PMC4812753