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Plant metabolism faces a challenge of investing enough enzymatic capacity to a pathway without overinvestment. As it takes energy and resources to build, operate, and maintain enzymes, there are benefits and drawbacks to accurately matching capacity to the pathway influx. The relationship between functional capacity and physiological load could be explained through symmorphosis, which would quantitatively match enzymatic capacity to pathway influx. Alternatively, plants could maintain excess enzymatic capacity to manage unpredictable pathway influx. In this study, we use photorespiration as a case study to investigate these two hypotheses in Betula papyrifera. This involves altering photorespiratory influx by manipulating the growth environment, via changes in CO2 concentration and temperature, to determine how photorespiratory capacity acclimates to environmental treatments. Surprisingly, the results from these measurements indicate that there is no plasticity in photorespiratory capacity in B. papyrifera, and that a fixed capacity is maintained under each growth condition. The fixed capacity is likely due to the existence of reserve capacity in the pathway that manages unpredictable photorespiratory influx in dynamic environments. Additionally, we found that B. papyrifera had a constant net carbon assimilation under each growth condition due to an adjustment of functional rubisco activity driven by changes in activation state. These results provide insight into the acclimation ability and limitations of B. papyrifera to future climate scenarios currently predicted in the next century.

Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone which is essential in eukaryotes. It is required for the activation and stabilization of a wide variety of client proteins and many of them are involved in important cellular pathways. Since Hsp90 affects numerous physiological processes such as signal transduction, intracellular transport, and protein degradation, it became an interesting target for cancer therapy. Structurally, Hsp90 is a flexible dimeric protein composed of three different domains which adopt structurally distinct conformations. ATP binding triggers directionality in these conformational changes and leads to a more compact state. To achieve its function, Hsp90 works together with a large group of cofactors, termed co-chaperones. Co-chaperones form defined binary or ternary complexes with Hsp90, which facilitate the maturation of client proteins. In addition, posttranslational modifications of Hsp90, such as phosphorylation and acetylation, provide another level of regulation. They influence the conformational cycle, co-chaperone interaction, and inter-domain communications. In this review, we discuss the recent progress made in understanding the Hsp90 machinery.

Ca 2+ /calmodulin-dependent protein kinase II (CaMKII) is an oligomeric enzyme with crucial roles in neuronal signaling and cardiac function. Previously, we showed that activation of CaMKII triggers the exchange of subunits between holoenzymes, potentially increasing the spread of the active state (Stratton et al., 2014; Bhattacharyya et al., 2016). Using mass spectrometry, we show now that unphosphorylated and phosphorylated peptides derived from the CaMKII-α regulatory segment bind to the CaMKII-α hub and break it into smaller oligomers. Molecular dynamics simulations show that the regulatory segments dock spontaneously at the interface between hub subunits, trapping large fluctuations in hub structure. Single-molecule fluorescence intensity analysis of CaMKII-α expressed in mammalian cells shows that activation of CaMKII-α results in the destabilization of the holoenzyme. Our results suggest that release of the regulatory segment by activation and phosphorylation allows it to destabilize the hub, producing smaller assemblies that might reassemble to form new holoenzymes.

Plant metabolism faces a challenge of investing enough enzymatic capacity to a pathway without overinvestment. As it takes energy and resources to build, operate, and maintain enzymes, there are benefits and drawbacks to accurately matching capacity to the pathway influx. The relationship between functional capacity and physiological load could be explained through symmorphosis, which would quantitatively match enzymatic capacity to pathway influx. Alternatively, plants could maintain excess enzymatic capacity to manage unpredictable pathway influx. In this study, we use photorespiration as a case study to investigate these two hypotheses in Betula papyrifera . This involves altering photorespiratory influx by manipulating the growth environment, via changes in CO 2 concentration and temperature, to determine how photorespiratory capacity acclimates to environmental treatments. Surprisingly, the results from these measurements indicate that there is no plasticity in photorespiratory capacity in B. papyrifera , and that a fixed capacity is maintained under each growth condition. The fixed capacity is likely due to the existence of reserve capacity in the pathway that manages unpredictable photorespiratory influx in dynamic environments. Additionally, we found that B. papyrifera had a constant net carbon assimilation under each growth condition due to an adjustment of functional rubisco activity driven by changes in activation state. These results provide insight into the acclimation ability and limitations of B. papyrifera to future climate scenarios currently predicted in the next century.

Erythromycin is one of the few compounds that remarkably increase ether-a-go-go-related gene (hERG) inhibition from room temperature (RT) to physiological temperature (PT). Understanding how erythromycin inhibits the hERG could help us to decide which compounds are needed for further studies. The whole-cell patch clamp technique was used to investigate the effects of erythromycin on hERG channels at different temperatures. While erythromycin caused a concentration-dependent inhibition of cardiac hERG channels, it also shifted the steady-state activation and steady-state inactivation of the channel to the left and significantly accelerated the onset of inactivation at both temperatures, although temperature itself caused a profound change in the dynamics of hERG channels. Our data also suggest that the binding pattern to S6 of the channels changes at PT. In contrast, cisapride, a well-known hERG blocker whose inhibition is not affected by temperature, does not change its critical binding sites after the temperature is raised to PT. Our data suggest that erythromycin is unique and that the shift in hERG inhibition may not apply to other compounds.

Lower limb tissue stiffness is contingent on various factors, including location, tissue composition, loading rates, and the geometry of the indenting object. Previous studies demonstrated that tissue stiffness varies greatly between individuals and between locations on an individual. Additionally, some studies have shown that activation of underlying muscle tissue increases bulk soft tissue stiffness. Yet, few studies have simultaneously considered both location and activation; this could be particularly important for measuring and predicting the function of devices such as prostheses and exoskeletons that interact with limbs at various locations during dynamic movement. In the present study, a custom handheld indentation device was used to explore changes in bulk leg tissue stiffness at rest and during isometric contractions. The indentation force-displacement curves were modelled using a Hertz model. At each level of activation (active/inactive), the shank had dramatically (∼150%) greater tissue stiffness than the thigh (p < 0.001). However, results suggested location independence for stiffness ratio (active/inactive, p = 0.42); for either location, stiffness was approximately 2x greater for active vs inactive muscle. These results should be considered during the development of biomechanical models to simulate human tissue indentation stiffness across a range of activation states and locations.

Whilst there has been investigation into the effect of time of the day on platelet activation and function in healthy individuals, there is a lack of studies in the literature to examine this relationship among platelet donors. We assessed the extent of platelet activation by percentage of platelets with surface-expressed P-selectin and flow cytometry in samples of whole blood from a group of qualified platelet donors (n = 84). The mean (SD) percentage of activated platelets in the pre-donation blood samples was 1.85 ± 1.57% (range 0.2-7.5%). In univariate analyses, the percentage of activated platelets was significantly and inversely correlated with the collection time (ie, the time of day blood samples were collected) (r = -0.35, p = 0.001) and positively correlated to mean platelet volume (MPV) (r = 0.29, p = 0.008). A weaker positive correlation was also observed with ABO blood group (r = 0.228, p = 0.036). Analysis of the collection time as a categorical variable showed a greater degree of activated platelets in samples collected between 8:00 h and 10:00 h than in samples collected during the hours of >10:00 h ≤14:00 h (2.5 ± 1.8 versus 1.1 ± 0.74, p < 0.001). In the adjusted linear regression model, collection time was a significant independent predictor of platelet activation state in whole blood (β = -0.26; p < 0.001), as did ABO blood group (β = 0.55; p = 0.019). Our results show that collection time is the most important predictor of platelet activation state in pre-donation whole blood among platelet donors. This work may have implications for optimizing the timing of platelet donation.

The cell surface glycoprotein CD44 displays different active statuses; however, it remains unknown whether the activation process of CD44 is critical for tumor development and progression. The aim of the present study was to investigate whether breast cancer (BCa) cells with different activation states of CD44 show similar or distinct functional characteristics and to further examine the mechanisms regulating CD44 activities. A feature for the 'activated' state of CD44 is that it can bind to its principal ligand hyaluronan (HA). The binding of CD44 with HA is usually influenced by CD44 alternative splicing, resulting in multiple CD44 isoforms that determine CD44 activities. Flow cytometry was used to sort BCa cell subsets based on CD44-HA binding abilities (HA−/low vs. HAhigh). Subsequently, cell proliferation and colony formation assays were performed in vitro, and CD44 expression patterns were analyzed via western blotting. The results demonstrated that the CD44 variant isoform 10 (CD44v10) was highly expressed in a HA−/low binding subset of BCa cells, which exhibited a significantly higher proliferation capacity compared with the HAhigh binding subpopulation. Knockdown of CD44v10 isoform in HA−/low binding subpopulation induced an increase in HA binding ability and markedly inhibited proliferation. Furthermore, the mechanistic analysis identified that CD44v10 facilitated cell proliferation via activation of ERK/p38 MAPK and AKT/mTOR signaling. Moreover, the knockdown of CD44v10 expression downregulated the phosphorylation of ERK, AKT and mTOR, while no alteration was observed in p38 phosphorylation. Collectively, the present study identified a subset of fast-growing BCa cells characterized by CD44v10 expression, which may serve as a specific therapeutic target for BCa.

The activation of the dodecameric Ca2+/calmodulin dependent kinase II (CaMKII) holoenzyme is critical for memory formation. We now report that CaMKII has a remarkable property, which is that activation of the holoenzyme triggers the exchange of subunits between holoenzymes, including unactivated ones, enabling the calcium-independent phosphorylation of new subunits. We show, using a single-molecule TIRF microscopy technique, that the exchange process is triggered by the activation of CaMKII, and that exchange is modulated by phosphorylation of two residues in the calmodulin-binding segment, Thr 305 and Thr 306. Based on these results, and on the analysis of molecular dynamics simulations, we suggest that the phosphorylated regulatory segment of CaMKII interacts with the central hub of the holoenzyme and weakens its integrity, thereby promoting exchange. Our results have implications for an earlier idea that subunit exchange in CaMKII may have relevance for information storage resulting from brief coincident stimuli during neuronal signaling. How do fleeting signals passing through the neurons of our brains become memories that can last for years or even decades? An enzyme called CaMKII is known to have an important role in the formation of memories. CaMKII adds phosphate groups to proteins—a process that is called phosphorylation—and is itself activated when calcium levels increase inside the neurons where the enzyme is found. Individual CaMKII proteins bind together in groups of 12 to form a ‘holoenzyme’. When one of the 12 subunits is activated by calcium, it can phosphorylate the other subunits in the same holoenzyme. Once this happens, the activation of CaMKII can continue after the initial rise in calcium has ceased, and this effect is thought to be involved in the formation of long-term memories. 30 years ago, Francis Crick—famous for his role in the discovery of the double helix—proposed that memory formation might involve ‘memory-storage molecules’ passing an activated state to unactivated molecules, and John Lisman later suggested that CaMKII could fulfil this role by swapping subunits of holoenzymes between activated and unactivated ones. Now, Stratton, Lee et al. have tested whether CaMKII can exchange subunits by using advanced microscopy to track single molecules of CaMKII labelled with fluorescent markers. This revealed that activation can cause CaMKII subunits repeatedly to mix between holoenzymes—and this only happens once a first holoenzyme has been activated. Subunits of CaMKII join together via a central ‘hub’ region, but when a subunit is activated, the phosphorylated segment may interact with the hub. This weakens the connections between the subunits, thereby making it easier for subunits to exchange between holoenzymes. This process provides a mechanism by which a level of activated CaMKII can be maintained, even if some subunits become degraded and long after the disappearance of the initial activation signal.

Neuroinflammatory processes are increasingly recognized as central to the pathophysiology of diverse central nervous system (CNS) disorders, including major depressive disorder (MDD), Alzheimer’s disease (AD), and Parkinson’s disease (PD). Microglia, the resident immune effector cells of the CNS, are key regulators of neuroimmune responses and engage in bidirectional communication with the serotonergic system. Activation of microglia toward a pro-inflammatory phenotype can disrupt serotonergic neurotransmission by altering the expression and function of the serotonin transporter (SERT) and modulating downstream 5-HT receptor signaling pathways. Conversely, serotonergic neurotransmission—mediated through receptor subtypes such as 5-HT 1A , 5-HT 2A / 2B , and 5-HT 7 —can regulate microglial phenotypic polarization and cytokine production, thereby influencing the inflammatory milieu and CNS homeostasis. This review synthesizes current evidence on the dynamic interplay between microglial activation states and serotonergic signaling, emphasizing their mutual contributions to disease onset and progression. Furthermore, we examine the therapeutic potential of targeting this neuroimmune interface using pharmacological strategies, including selective serotonin reuptake inhibitors (SSRIs), anti-inflammatory agents, and receptor-specific ligands. Clarifying this bidirectional crosstalk may inform the development of innovative interventions for neuroinflammation-associated neuropsychiatric and neurodegenerative disorders.