Biology subjects

MAITI, S.

Publications and source records attributed to MAITI, S..

9 recordsLinked to original sources

bioRxiv2026

Vibrio cholerae VgrG1-ACD Targets E. coli MreB and Regulates Cellular Morphology

Vibrio cholerae employs the Type VI Secretion System (T6SS) to outcompete neighboring bacteria and establish successful colonization within the polymicrobial gut. The T6SS effector VgrG1 contains a C-terminal Actin Crosslinking Domain (VgrG1-ACD), well known for irreversibly crosslinking eukaryotic actin to disrupt the host cytoskeleton. However, whether VgrG1-ACD also contributes directly to interbacterial competition has remained unexplored. Here, we identify a previously unrecognized bacterial target of VgrG1-ACD: MreB, the bacterial actin homolog essential for cell shape, cell wall synthesis, and cytoskeletal organization. We demonstrate that VgrG1-ACD specifically binds Escherichia coli MreB, resulting in pronounced morphological defects and impaired bacterial growth. Notably, unlike its activity toward mammalian actin, VgrG1-ACD targets MreB without crosslinking it, revealing a distinct mode of action. These findings expand the functional repertoire of VgrG1-ACD beyond host-directed virulence and uncover a dual-targeting strategy through which a single T6SS effector manipulates both mammalian actin and its bacterial homolog, likely enhancing V. cholerae fitness during interbacterial competition and host colonization.

microbiology↗

bioRxiv2026

Dual Regulatory Role of Nuclear FNBP4 in Actin Binding and Formin FMN1 Inhibition

Nuclear actin dynamics are increasingly recognized as central to genome regulation, yet the identity and function of dedicated nuclear actin regulators remain elusive. Here, we uncover formin-binding protein 4 (FNBP4) as a previously uncharacterized nuclear actin-binding protein that integrates dual regulatory functions. We identify a conserved basic KRRK motif within its C-terminal that directly interacts actin and coincides with a non-canonical nuclear localization signal. In parallel, FNBP4 interacts with the formin FMN1 via its N-terminal WW domains, potently suppressing FMN1-mediated actin nucleation. Strikingly, full-length FNBP4, which unites both the FMN1- and actin-binding modules, displays synergistic inhibition far exceeding that of truncated fragments. Furthermore, confocal imaging confirms nuclear colocalization of FNBP4 with actin, highlighting its role in shaping nuclear actin architecture. Our findings position FNBP4 as the first example of a nuclear-resident formin inhibitor that simultaneously binds actin and a formin. This dual functionality establishes a new regulatory paradigm in which a single protein integrates direct actin interaction with formin inhibition to fine-tune nuclear actin organization.

biochemistry↗

bioRxiv2025

Deciphering the Interaction Between Dvl2 and Profilin2: Effector Molecules of Non-Canonical Wnt Signaling

Wnt signalling is a cornerstone of embryonic development, orchestrating critical processes such as body axis formation, gastrulation, and organogenesis through conserved canonical and non-canonical pathways. Dishevelled (Dvl), a central mediator of these pathways, contains conserved DIX, PDZ, and DEP domains, along with an extreme-C-terminus. Recent studies suggest that the extreme-C-terminus regulates non-canonical Wnt signalling via an autoinhibitory interaction with the PDZ domain. Non-canonical Wnt signalling branches into the planar cell polarity (PCP) and Wnt/Ca{superscript 2} pathways. Profilin, a monomeric actin-binding protein, has been implicated in PCP signalling through Daam1-mediated actin polymerization, whereas its silencing disrupts the Wnt/Ca{superscript 2} pathway in a Daam1-independent manner, pointing to a role for profilin upstream of Daam1. In this study, we identify a novel interaction between Dvl2 and profilin2. Co-localization and in vitro pull-down assays demonstrate that profilin2 directly interacts with Dvl2. Furthermore, our study reveals profilin2 binds specifically to the extreme-C-terminus of Dvl2, beyond the polyproline motif, without engaging the PDZ or DEP domains. This challenges the conventional view of profilin-polyproline interactions and highlights the existence of previously unrecognized molecular determinants. Moreover, we show that Dvl2 adopts an autoinhibited conformation through intramolecular binding of its extreme-C-terminus to the PDZ domain. Remarkably, profilin2 retains its binding ability even in this autoinhibited state. Together, these findings uncover a previously unrecognized profilin2-Dvl2 interaction and provide new mechanistic insights into the molecular regulation of non-canonical Wnt signalling.

developmental biology↗

bioRxiv2024

Mechanistic Insights into FNBP4-Mediated Regulation of non-diaphanous Formin FMN1 in Actin Cytoskeleton Dynamics

Formin1 (FMN1), a member of the non-diaphanous formin family, is essential for development and neuronal function. Unlike diaphanous-related formins, FMN1 is not subject to canonical autoinhibition through the DID and DAD domains, nor is it activated by Rho GTPase binding. Recent studies suggest that formins also play roles in the nucleus, influencing DNA damage response and transcriptional regulation. However, the mechanisms regulating nuclear formins particularly non-diaphanous ones like FMN1 remain poorly understood. Our previous research identified the interaction between FMN1 and FNBP4, prompting further investigation into its functional role in regulating actin dynamics. Results reveal that FNBP4 inhibits FMN1-mediated actin assembly in vitro. It is shown that FNBP4 prevents FMN1 from displacing the capping protein CapZ at the growing barbed end of actin filaments. Additionally, FNBP4 inhibits FMN1s bundling activity in a concentration-dependent manner. Further analysis indicates that FNBP4 interacts with the FH1 domain and the interdomain connector between the FH1 and FH2 domains, creating spatial constraints on the FH2 domain. We propose that FNBP4 acts as a stationary inhibitor of FMN1. In addition, we identify a monopartite nuclear localization signal (NLS) in FNBP4, and subcellular localization studies show that FNBP4 colocalizes with FMN1. This study provides new insights into the regulatory role of FNBP4 in modulating FMN1-mediated actin dynamics, suggesting that FNBP4 may function as a nuclear inhibitor of actin polymerization and shedding light on regulatory mechanisms specific to non-diaphanous formins.

cell biology↗

bioRxiv2023

A novel role of macrophage PIST protein in regulating Leishmania major infection

PDZ protein interacting specifically with Tc10 or PIST is a mammalian trans-Golgi resident protein that regulates subcellular sorting of plasma membrane receptors. PIST has recently been found to play an important role in regulating viral pathogenesis. Alteration in PIST expression is linked to the reprogramming of cell surface receptors which is crucial in determining herpes simplex virus1 infection. In this context, PIST is crucial in triggering autophagy via Beclin 1 -PI3KC3 pathway. However, there is complete lack in our knowledge on the role of this protein in any parasitic infection. Leishmania parasites infect their host macrophage cells via phagocytosis and their survival within the parasitophorous compartment has recently been found to be dependent on host autophagy by a yet to be identified mechanism. Using Leishmania major (L. major)-macrophage infection model system we, for the first-time report here that in infected macrophages Golgi resident PIST protein migrates towards the parasite containing compartment. We have also found that PIST associates with Beclin 1, however, not with LC3 within L. major parasite containing compartment of infected macrophages. Further, we performed genetic ablation of PIST by siRNA and observed that knockdown of macrophage PIST in turn helps in parasite replication. Contrary to this, overexpression of PIST in macrophages restricted the multiplication of L. major. Collectively, our study for the first time reveals that PIST is essential in regulating intracellular parasite, L. major infection within macrophage cells. Summary StatementMammalian PIST protein plays a crucial role in regulating cellular trafficking events. Here, we showed that PIST status is altered within Leishmania major parasite infected macrophages. Further, we confirmed that PIST is essential in restricting parasite growth. Additionally, a potential interacting axis between PIST and Beclin 1 is identified during infection.

cell biology↗

bioRxiv2023

Probing the ligand binding specificity of FNBP4 WW domains and interaction with FH1 domain of FMN1

Formins are a group of actin-binding proteins that mediate nascent actin filament polymerization, filament elongation, and barbed end capping function, thereby regulating different cellular and developmental processes. Developmental processes like vertebrate gastrulation, neural growth cone dynamics, and limb development require formins to function in a regulated manner. Formin binding proteins like Rho GTPase regulates activation of auto-inhibited conformation of diaphanous formins. Unlike other diaphanous formins, Formin1 (FMN1), a non-diaphanous formin, is not regulated by Rho GTPase. FMN1 acts as an antagonist of the BMP signaling pathway during limb development. Several previous reports demonstrated that WW domain-containing proteins can interact with poly-proline-rich amino acid stretches of formins and play a crucial role in developmental processes. WW domain-containing FNBP4 protein plays an essential role in limb development. It has been hypothesized that the interaction between FNBP4 and FMN1 can further attribute to the role in limb development through the BMP signaling pathway. In this study, we have elucidated the binding kinetics of FNBP4 and FMN1 using surface plasmon resonance and enzyme-linked immunosorbent assays. Our findings confirm that the FNBP4 exhibits interaction with the poly-proline-rich formin homology 1 (FH1) domain of FMN1. Furthermore, only the first WW1 domains is involved in the interaction between the two domains. Thus, this study sheds light on the binding potentialities of WW domains of FNBP4 and their possible contribution to the regulation of FMN1 function.

cell biology↗

bioRxiv2021

Leishmania major formins are cytosolic actin bundler play an important role in cell physiology

Formins are a highly conserved eukaryotic family of proteins that regulate actin dynamics. They play important physiological roles in cell adhesion, motility, vesicular trafficking and cytokinesis. Although sequence analysis of Trypanosomatida genomes predicted multiple formin-encoding genes, none of them are functionally characterized yet. We report here experimental identification and functional characterization of two constitutively expressed formins from the trypanosomatid protozoa Leishmania major viz. LmForminA and LmForminB. These formins exhibited irregular cytosolic distribution that co-localized with actin patches. Co-sedimentation assay and surface plasmon resonance confirmed that purified LmForminA and B FH2 domains can bind actin, albeit with differential affinity. Interestingly, both LmForminA and B FH2 domains were found to be actin bundlers as revealed by low-speed co-sedimentation assay and TIRF microscopy. LmForminA and B also had actin-nucleating activities, which was abolished by mutating their conserved Ile residue crucial for actin assembly. The Ile-mutant formins, however, retained their actin binding and bundling properties. Treatment of Leishmania cells with formin inhibitor SMIFH2 severely perturbed parasite growth and morphology indicating that Lmformins are physiologically important and may be considered as novel drug targets.

cell biology↗

bioRxiv2018

nPIST: A Novel Actin Binding Protein of trans-Golgi Network

npist is the neuronal isoform of PIST, a trans-golgi associated protein involved in major modulation of vesicular trafficking. nPIST interacts with glutamate delta2 receptor (GluR{delta}2) in Purkinje cells. Our study shows nPIST as a novel actin binding protein. Our structure based sequence analysis shows nPIST contains one WH2-like domain. Further our experimental analysis illustrates that fragment of nPIST consisting of WH2-like domain binds to actin. Moreover it was found that nPIST contains several regions involved in interaction with actin. The binding of nPIST to actin through multiple actin binding regions facilitated actin filament stabilization in vitro. In vivo, nPIST localized actin in perinuclear region as a blotch when ectopically expressed.

cell biology↗

bioRxiv2016

Non Diaphanous Formin Delphilin Acts as a Barbed End Capping Protein

Formins are important for actin polymerization. Delphilin is a unique formin having PDZ domains and FH1, FH2 domains at its N and C terminus respectively. In this study we observed that Delphilin binds to actin filaments, and have negligible actin filament polymerizing activity. Delphilin inhibits actin filament elongation like barbed end capping protein CapZ. In vitro, Delphilin stabilized actin filaments by inhibiting actin filament depolymerisation. Therefore, our study demonstrates Delphilin as an actin-filament capping protein.

cell biology↗