Biology subjects

Ataullakhanov, F. I.

Publications and source records attributed to Ataullakhanov, F. I..

7 recordsLinked to original sources

bioRxiv2026

Burst-like Secretion of Platelet Dense Granules Promotes Thrombus Shell Expansion

Vessel-wall injury triggers platelet recruitment and aggregation with exquisite spatiotemporal regulation. While secreted agonists from thrombin-activated platelets play a crucial role in thrombus formation, the underlying mechanisms remain elusive. Using real-time imaging of isolated human platelets, we demonstrate that dense granules, which are enriched with agonists, are released in brief, stochastic bursts driven by intracellular calcium spikes, which are necessary but not individually sufficient to trigger secretion events. This burst-like secretion is sustained through extracellular feedback, establishing a cooperative, probabilistic mechanism of granule release in which released agonists amplify thrombin-induced granule exocytosis and increase the likelihood of secretion bursts. Computational modeling of whole-thrombus growth reveals that these transient bursts generate localized microdomains of high agonist concentration, facilitating expansion of the outer thrombus layers. Our findings establish burst-like secretion as a distinct hemostatic mechanism that enhances platelet recruitment and orchestrates thrombus architecture through localized, self-reinforcing activation. Key pointsO_LILive imaging reveals dense granules secretion in discrete bursts. C_LIO_LIIntracellular calcium spikes are necessary but not sufficient for triggering secretion events. C_LIO_LIBurst-like secretion arises from cooperativity, driven by the feedback amplification from the extracellularly released granule content. C_LIO_LIBurst-like dense granule secretion promotes dynamic expansion of the thrombus shell in silico. C_LI

cell biology↗

bioRxiv2026

Hidden Complexity of Pediatric Platelet Disorders: Functional Diversity and Unexpected Hypercoagulable Phenotypes

Pediatric platelet disorders are commonly classified according to specific structural or functional abnormalities, yet it remains unclear how well these diagnoses capture overall hemostatic phenotype. Here, we combined quantitative single-cell platelet measurements with spatially resolved plasma clotting analysis to characterize pediatric patients with dense granule deficiency, platelet function defects, immune thrombocytopenia, and other inherited platelet disorders. Quantitative fluorescence microscopy revealed reduced dense granule abundance not only in dense granule deficiency but also in several patients from other diagnostic groups. Measurements of platelet adhesion, spreading, and calcium signaling identified substantial functional diversity, with individual patients exhibiting distinct combinations of abnormalities that were not predicted by diagnostic category. Unexpectedly, plasma clotting analysis frequently revealed hypercoagulable behavior, including accelerated fibrin clot growth and spontaneous fibrin formation, despite clinical diagnoses associated with platelet-related bleeding disorders. Hypercoagulable phenotypes occurred across multiple diagnostic groups and did not show a simple relationship with platelet functional abnormalities. Together, these findings reveal previously unrecognized complexity in pediatric platelet disorders and suggest that platelet and plasma pathways contribute independently to hemostatic variability. These findings argue that pediatric platelet disorders are best viewed as multidimensional functional phenotypes rather than isolated platelet defects and motivate broader integration of platelet and coagulation measurements in future studies.

cell biology↗

bioRxiv2025

Ndc80 complex, a conserved coupler for kinetochore-microtubule motility, is a sliding molecular clutch

Chromosome motion at spindle microtubule plus-ends relies on dynamic molecular bonds between kinetochores and proximal microtubule walls. Under opposing forces, kinetochores move bi-directionally along these walls while remaining near the ends, yet how continuous wall-sliding occurs without end-detachment remains unclear. Using ultrafast force-clamp spectroscopy, we show that single Ndc80 complexes, the primary microtubule-binding kinetochore component, exhibit processive, bi-directional sliding. Plus-end-directed forces induce a mobile catch-bond in Ndc80, increasing frictional resistance and restricting sliding toward the tip. Conversely, forces pulling Ndc80 away from the plus-end trigger mobile slip-bond behavior, facilitating sliding. This dual behavior arises from force-dependent modulation of the Nuf2 calponin-homology domains microtubule binding, identifying this subunit as a friction regulator. We propose that Ndc80cs ability to modulate sliding friction provides the mechanistic basis for the kinetochores end coupling, enabling its slip-clutch behavior. One Sentence SummaryDirection-dependent mobile catch- and slip-bond behavior of the microtubule-binding Ndc80 protein

biophysics↗

bioRxiv2024

Molecular density-accelerated binding-site maturation underlies CENP-T-dependent kinetochore assembly

Macromolecular assembly depends on tightly regulated pairwise binding interactions that are selectively favored at assembly sites while being disfavored in the soluble phase. This selective control can arise due to molecular density-enhanced binding, as recently found for the kinetochore scaffold protein CENP-T. When clustered, CENP-T recruits markedly more Ndc80 complexes than its monomeric counterpart, but the underlying molecular basis remains elusive. Here, we use quantitative in vitro assays to reveal two distinct mechanisms driving this behavior. First, Ndc80 binding to CENP-T is a two-step process: initially, Ndc80 molecules rapidly associate and dissociate from disordered N-terminal binding sites on CENP-T. Over time, these sites undergo maturation, resulting in stronger Ndc80 retention. Second, we find that this maturation transition is regulated by a kinetic barrier that is sensitive to the molecular environment. In the soluble phase, binding site maturation is slow, but within CENP-T clusters, this process is markedly accelerated. Notably, the two Ndc80 binding sites in human CENP-T exhibit distinct maturation rates and environmental sensitivities, which correlate with their different amino-acid content and predicted binding conformations. This clustering-induced maturation is evident in dividing human cells, suggesting a distinct regulatory entry point for controlling kinetochore assembly. We propose that the tunable acceleration of binding site maturation by molecular crowding may represent a general mechanism for promoting the formation of macromolecular structures. Significance StatementA distinctive mechanism of protein-protein interaction underpins the assembly of kinetochores, which is critical for human cell division. During mitosis, the Ndc80 complex must bind tightly to the unstructured N-terminus of its receptor, CENP-T, which is densely clustered at kinetochores. Using single-molecule in vitro assays, we show that Ndc80 binding is mediated by an initially unstable yet tunable interface. The high molecular density of CENP-T at the kinetochores accelerates the maturation of this binding interface, favoring the formation of stable complexes within the kinetochore structure, rather than in the soluble phase. This environment-driven modulation of binding site maturation may represent a key regulatory mechanism for ensuring strong and specific interactions during the assembly of macromolecular complexes such as kinetochores.

biophysics↗

bioRxiv2022

Significance of two transmembrane ion gradients for human erythrocyte volume stabilization.

Functional completeness of erythrocytes depends on high deformability of these cells, that allows them to pass through narrow tissue capillaries. The erythrocytes high deformability is provided due to maintenance of discoid shape with an optimal cell surface area to volume ratio. This ratio can be maintained due to cell volume stabilization at a given cell surface area. We studied role of Na/K-ATPase and transmembrane Na+ and K+ gradients in human erythrocyte volume stabilization at non-selective increase in cell membrane permeability to cations by using mathematical simulation. The simulation took into account a contribution of glycolytic metabolites and adenine nucleotides to cytoplasm osmotic pressure in the cells. It was shown that in the presence of Na/K-ATPase activated by intracellular sodium ions and two oppositely directed gradients of Na+ and K+ ions in the cell, the volume of the erythrocyte deviates from the optimal value by no more than 10% with a change in the non-selective permeability of the cell membrane to cations from 50 to 200% of the normal value. The transport Na/K-ATPase, which sets the ratio of transmembrane fluxes of sodium and potassium ions equal to 3:2, provides the best stabilization of the erythrocyte volume exactly at a non-selective increase in the permeability of the cell membrane, when the permeability for sodium and potassium ions increases equally. Such increase in erythrocyte membrane permeability is caused by oxidation of the membrane components and by mechanical stress during circulation. In the case of only one transmembrane ion gradient (Na+), the cell loses the ability to stabilize the volume when the cell membrane is damaged. In this case even small variations of cell membrane permeability cause dramatic changes in the cell volume. Our results reveal that the presence of two oppositely directed transmembrane ion gradients (Na+ and K+) and the transport Na/K-ATPase activated by intracellular sodium are fundamentally important conditions for the stabilization of cellular volume in human erythrocytes.

systems biology↗

bioRxiv2018

Molecular requirements for transition from lateral to end-on microtubule binding and dynamic coupling

Accurate chromosome segregation relies on microtubule end conversion, the ill-understood ability of kinetochores to transit from lateral microtubule attachment to durable association with dynamic microtubule plus-ends. The molecular requirements for this conversion and the underlying biophysical mechanisms are ill-understood. We reconstituted end conversion in vitro using two kinetochore components: the plus end-directed kinesin CENP-E and microtubule-binding Ndc80 complex, combined on the surface of a microbead. The primary role of CENP-E is to ensure close proximity between Ndc80 complexes and the microtubule plus-end, whereas Ndc80 complexes provide lasting microtubule association by diffusing on the microtubule wall near its tip. Together, these proteins mediate robust plus-end coupling during several rounds of microtubule dynamics, in the absence of any specialized tip-binding or regulatory proteins. Using a Brownian dynamics model, we show that end conversion is an emergent property of multimolecular ensembles of microtubule wall-binding proteins with finely tuned force-dependent motility characteristics.

cell biology↗

bioRxiv2016

CENP-F couples cargo to growing and shortening microtubule ends

Dynamic microtubule ends exert pulling and pushing forces on intracellular membranes and organelles. However, the mechanical linkage of microtubule tips to their cargoes is poorly understood. CENP-F is a non-motor microtubule-binding protein that participates in microtubule binding at kinetochores and in the mitotic redistribution of the mitochondrial network. CENP-F-driven mitochondrial transport is linked to growing microtubule tips, but the underlying molecular mechanisms are unknown. Here we show that CENP-F tracks growing microtubule ends in living cells. In vitro reconstitution demonstrates that microtubule tips can transport mitochondria and CENP-F-coated artificial cargoes over micrometer-long distances, during both growing and shrinking phases. Based on these and previous observations, we suggest that CENP-F might act as a transporter of mitochondria and other cellular cargoes by attaching them to dynamic microtubule ends.

cell biology↗