Ataullakhanov, F. | bioRxiv Science

bioRxiv2022

CLASP2 stabilizes GDP-associated terminal tubulins to prevent microtubule catastrophe

CLASPs are ubiquitous stabilizers of microtubule dynamics but their molecular targets at the microtubule plus-end are not understood. Using DNA origami-based reconstructions we show that clusters of human CLASP2 form a load-bearing bond with terminal GDP-tubulins at the stabilized microtubule tip. This activity relies on the unconventional TOG2 domain of CLASP2, which releases its high-affinity bond with the GDP-dimers upon their conversion into polymerization-competent GTP-tubulin. By tethering dynamic microtubule ends near immobilized CLASP2, we show that the targets for CLASP2 binding at the polymerizing tip arise stochastically, leading to nanoscale disruptions in microtubule tip integrity. The ability of CLASP2 to recognize nucleotide-specific tubulin conformation and stabilize the catastrophe-promoting GDP-tubulins intertwines with the previously underappreciated exchange between GDP and GTP at terminal tubulins, providing a distinct molecular mechanism to suppress microtubule catastrophe without affecting tubulin incorporation.

biophysics↗

bioRxiv2020

Platelet, erythrocyte, endothelial, and monocyte microparticles in coagulation activation and propagation

Background and objectiveFor many pathological states, microparticles are supposed to be one of the causes of hypercoagulation. Although there are some indirect data about microparticles participation in coagulation activation and propagation, the integral hemostasis test Thrombodynamics allows to measure micropaticles participation in these two coagulation phases directly by influence on the appearance of coagulation centers in plasma volume and on the rate of clot grown from surface with immobilized tissue factor. MethodsMicroparticles were obtained from platelets and erythrocytes by stimulation with SFLLRN and A23187, respectively, from monocytes, endothelial HUVEC culture and monocytic THP cell culture by stimulation with lipopolysaccharides. Microparticles were counted by flow cytometry and titrated in microparticle-depleted normal plasma in the Thrombodynamics test. ResultsMonocyte microparticles induced the appearance of clotting centres through the TF pathway at concentrations approximately 100-fold lower than platelet and erythrocyte microparticles, which activated plasma by the contact pathway. For endothelial microparticles, both activation pathways were essential, and their activity was intermediate. Monocyte microparticles induced plasma clotting by the appearance of hundreds of clots with an extremely slow growth rate, while erythrocyte microparticles induced the appearance of a few clots with a growth rate similar to that from surface covered with high-density tissue factor. Patterns of clotting induced by platelet and endothelial microparticles were intermediate. Platelet, erythrocyte and endothelial microparticles impacts on the rate of clot growth from the surface with tissue factor did not differ significantly within the 0-200{middle dot}103/ul range of microparticles concentrations. However, at concentrations greater than 500{middle dot}103/ul, erythrocyte microparticles increased the stationary clot growth rate to significantly higher levels than do platelet microparticles or artificial phospholipid vesicles consisting of phosphatidylcholine and phosphatidylserine. ConclusionMicroparticles of different origins demonstrated qualitatively different characteristics related to coagulation activation and propagation.

biophysics↗