Biology subjects

Dwyer, M. E.

Publications and source records attributed to Dwyer, M. E..

3 recordsLinked to original sources

bioRxiv2024

Orthogonality of shell proteins across BMC subclasses in cyanobacteria

Bacterial microcompartments (BMC) are protein-based organelles broadly distributed across all bacterial phyla and subclassified into [≥]60 functional variants. Despite their evolutionary and metabolic diversity, shell proteins that structurally compose the BMC surface are closely related across BMC classes. Herein, we sought to identify molecular and physiological features that could promote independent operation of more than one BMC type within the same cell by reducing inter-organelle cross-talk of shell proteins. We heterologously expressed shell proteins from the structurally well-defined BMC of Haliangium ochraceum (HO) within Synechococcus elongatus PCC 7942, a model cyanobacterium containing the {beta}-carboxysome. We find considerable cross-reactivity of the HO hexameric shell protein (HO BMC-H) with components of the {beta}-carboxysome; HO BMC-H can integrate into carboxysomes, disrupt its ultrastructural organization, and impair its associated CO2 fixation reactions. S. elongatus is unable to maintain the integrity of the {beta}-carboxysome over time when HO BMC-H is expressed in the absence of one or more of three broad strategies that act to increase the orthogonality between HO and carboxysome BMC shell proteins: i) reduced expression of promiscuous shell proteins; ii) sequestration of free HO BMC-H proteins via co-expression of other members of the same HO shell protein class, or; iii) heterologous expression of BMC positional system proteins McdAB (Maintenance of carboxysome distribution AB), revealing a putative moonlighting function of the McdAB protein family. Our results have implications for bacteria that encode more than one BMC within their genome and may have translational implications for the use of engineered BMCs for biotechnological applications.

synthetic biology↗

bioRxiv2022

Nonlinear microscale mechanics of actin networks governed by coupling of filament crosslinking and stabilization

Actin plays a vital role in maintaining the stability and rigidity of biological cells while allowing for cell motility and shape change. The semiflexible nature of actin filaments - along with the myriad actin-binding proteins (ABPs) that serve to crosslink, bundle, and stabilize filaments - are central to this multifunctionality. The effect of ABPs on the structural and mechanical properties of actin network mechanics has been the topic of fervent investigation over the past few decades, revealing diverse structures from isotropic percolated networks to heterogeneous bundles that depend on the crosslinker type and concentration. Yet, the impact of filament stabilization and stiffening via ABPs on the nonlinear response of crosslinked networks has yet to be explored. Here, we perform optical tweezers microheology measurements to characterize the nonlinear force response and relaxation dynamics of actin networks in the presence of varying concentrations of -actinin, which transiently crosslinks actin filaments, and phalloidin, which stabilizes filamentous actin and increases its persistence length. We show that crosslinking and stabilization can act both synergistically and antagonistically to tune the network resistance to nonlinear straining. For example, phalloidin-stabilization leads to enhanced elastic response and reduced dissipation at large strains and timescales, while the initial microscale force response is reduced compared to networks without phalloidin. Moreover, we find that stabilization switches this initial response from that of stress-stiffening to softening despite the increased filament stiffness that phalloidin confers. Finally, we show that both crosslinking and stabilization are necessary to elicit these emergent features, while the effect of stabilization on networks without crosslinkers is much more subdued. We suggest that these intriguing mechanical properties arise from the competition and cooperation between filament connectivity, bundling, and rigidification, shedding light on how ABPs with distinct roles can act in concert to mediate diverse mechanical properties of the cytoskeleton and bio-inspired polymeric materials.

biophysics↗

bioRxiv2021

Light-dependent THRUMIN1 phosphorylation regulates its association with actin filaments and 14-3-3 proteins

Light-dependent chloroplast movements in leaf cells contribute to the optimization of photosynthesis. Low light conditions induce chloroplast accumulation along periclinal cell surfaces, providing greater access to the available light, whereas high light induces movement of chloroplasts to anticlinal cell surfaces providing photodamage protection and allowing more light to reach underlying cell layers. The THRUMIN1 protein is required for normal chloroplast movements in Arabidopsis thaliana and has been shown to localize at the plasma membrane and to undergo rapid light-dependent interactions with actin filaments through the N-terminal intrinsically disordered region. A predicted WASP-Homology 2 (WH2) domain was found in the intrinsically disordered region but mutations in this domain did not disrupt localization of THRUMIN1:YFP to actin filaments. A series of other protein truncations and site-directed mutations of known and putative phosphorylation sites indicated that a phosphomimetic mutation (serine to aspartic acid) at position 170 disrupted localization of THRUMIN1 with actin filaments. However, the phosphomimetic mutant rescued the thrumin1-2 mutant phenotype for chloroplast movement and raises questions about the role of THRUMIN1s interaction with actin. Mutation of serine 146 to aspartic acid also resulted in cytoplasmic localization of THRUMIN1:YFP in Nicotiana benthamiana. Mutations to a group of putative zinc-binding cysteine clusters implicates the C-terminus of THRUMIN1 in chloroplast movement. Phosphorylation-dependent association of THRUMIN1 with 14-3-3 KAPPA and OMEGA were also identified. Together, these studies provide new insights into the mechanistic role of THRUMIN1 in light-dependent chloroplast movements. One Sentence SummarySite-directed mutagenesis of THRUMIN1 revealed critical sites involved in blue light-dependent localization of THRUMIN1 to actin filaments, 14-3-3 proteins, and its regulation of chloroplast movement.

cell biology↗