Direct Evidence for Specific Interactions of the Fibrinogen αC-Domains with the Central E Region and with Each Other †

The carboxyl-terminal regions of the fibrinogen Aα chains (αC regions) form compact αC-domains tethered to the bulk of the molecule with flexible αC-connectors. It was hypothesized that in fibrinogen two αC-domains interact intramolecularly with each other and with the central E region preferentially through its N-termini of Bβ chains, and that removal of fibrinopeptides A and B upon fibrin assembly results in dissociation of the αC regions and their switch to intermolecular interactions. To test this hypothesis, we studied the interactions of the recombinant αC region (Aα221-610 fragment) and its sub-fragments, αC-connector (Aα221-391) and αC-domain (Aα392-610), between each other and with the recombinant (Bβ1-66)2 and (β15-66)2 fragments and NDSK corresponding to the fibrin(ogen) central E region, using laser tweezers-based force spectroscopy. TheαC-domain, but not the αC-connector, bound to NDSK, which contains fibrinopeptides A and B, and less frequently to desA-NDSK and (Bβ1-66)2 containing only fibrinopeptides B; it was poorly reactive with desAB-NDSK and (β15-66)2 both lacking fibrinopeptides B. The interactions of the αC-domains with each other and with the αC-connector were also observed, although they were weaker and heterogeneous in strength. These results provide the first direct evidence for the interaction between the αC-domains and the central E region through fibrinopeptides B, in agreement with the above hypothesis, and indicate that fibrinopeptides A are also involved. They also confirm the hypothesized homomeric interactions between the αC-domains and display their interaction with the αC-connectors, which may contribute to covalent cross-linking of α polymers in fibrin

The Interaction of Integrin α IIb β 3 with Fibrin Occurs through Multiple Binding Sites in the α IIb β-Propeller Domain

The currently available antithrombotic agents target the interaction of platelet integrin αIIbβ3 (GPIIb-IIIa) with fibrinogen during platelet aggregation. Platelets also bind fibrin formed early during thrombus growth. It was proposed that inhibition of platelet-fibrin interactions may be a necessary and important property of αIIbβ3 antagonists; however, the mechanisms by which αIIbβ3 binds fibrin are uncertain. We have previously identified the γ370–381 sequence (P3) in the γC domain of fibrinogen as the fibrin-specific binding site for αIIbβ3 involved in platelet adhesion and platelet-mediated fibrin clot retraction. In the present study, we have demonstrated that P3 can bind to several discontinuous segments within the αIIb β-propeller domain of αIIbβ3 enriched with negatively charged and aromatic residues. By screening peptide libraries spanning the sequence of the αIIb β-propeller, several sequences were identified as candidate contact sites for P3. Synthetic peptides duplicating these segments inhibited platelet adhesion and clot retraction but not platelet aggregation, supporting the role of these regions in fibrin recognition. Mutant αIIbβ3 receptors in which residues identified as critical for P3 binding were substituted for homologous residues in the I-less integrin αMβ2 exhibited reduced cell adhesion and clot retraction. These residues are different from those that are involved in the coordination of the fibrinogen γ404–411 sequence and from auxiliary sites implicated in binding of soluble fibrinogen. These results map the binding of fibrin to multiple sites in the αIIb β-propeller and further indicate that recognition specificity of αIIbβ3 for fibrin differs from that for soluble fibrinogen

Thermal structure and cooling of superfluid neutron stars with accreted magnetized envelopes

We study the thermal structure of neutron stars with magnetized envelopes composed of accreted material, using updated thermal conductivities of plasmas in quantizing magnetic fields, as well as equation of state and radiative opacities for partially ionized hydrogen in strong magnetic fields. The relation between the internal and local surface temperatures is calculated and fitted by an analytic function of the internal temperature, magnetic field strength, angle between the field lines and the normal to the surface, surface gravity, and the mass of the accreted material. The luminosity of a neutron star with a dipole magnetic field is calculated for various values of the accreted mass, internal temperature, and magnetic field strength. Using these results, we simulate cooling of superfluid neutron stars with magnetized accreted envelopes. We consider slow and fast cooling regimes, paying special attention to very slow cooling of low-mass superfluid neutron stars. In the latter case, the cooling is strongly affected by the combined effect of magnetized accreted envelopes and neutron superfluidity in the stellar crust. Our results are important for interpretation of observations of isolated neutron stars hottest for their age, such as RX J0822-43 and PSR B1055-52.Comment: 15 pages, 12 figures, 2 tables. Corrected title only (v2

Top quark mass definition and top quark pair production near threshold at the NLC

We suggest an infrared-insensitive quark mass, defined by subtracting the soft part of the quark self energy from the pole mass. We demonstrate the deep relation of this definition with the static quark-antiquark potential. At leading order in 1/m this mass coincides with the PS mass which is defined in a completely different manner. Going beyond static limit, the small normalization point introduces recoil corrections which are calculated here as well. Using this mass concept and other concepts for the quark mass we calculate the cross section of e+ e- -> t t-bar near threshold at NNLO accuracy adopting three alternative approaches, namely (1) fixing the pole mass, (2) fixing the PS mass, and (3) fixing the new mass which we call the PS-bar mass. We demonstrate that perturbative predictions for the cross section become much more stable if we use the PS or the PS-bar mass for the calculations. A careful analysis suggests that the top quark mass can be extracted from a threshold scan at NLC with an accuracy of about 100-200 MeV.Comment: published version, 21 pages in LaTeX including 11 PostScript figure

A new species of Dyspessa Hübner, (Lepidoptera, Cossidae) from Western China, with catalogue of Chinese species of the genus

Yakovlev, Roman V., Saldaitis, Aidas, Pekarsky, Oleg (2016): A new species of Dyspessa Hübner, (Lepidoptera, Cossidae) from Western China, with catalogue of Chinese species of the genus. Zootaxa 4107 (1): 85-88, DOI: http://doi.org/10.11646/zootaxa.4107.1.

Comparison of the mass distributions of short-period exoplanets detected by transit and RV methods

International audienceWe analyse the causes of a discrepancy between the earlier obtained samples of the mass distributions of exoplanets detected by the transit method and the radial velocity (RV) one and corrected for some observational selection effects. It is found that this discrepancy can be removed by introducing the following restrictions into the procedures forming the samples: (i) to consider, among transit exoplanets, only those which masses were determined by the RV method (i.e. excluding the TTV method); (ii) to take into account exoplanets with orbital periods P ∈ [1, 100] days and masses M ∈ [0.02, 13]MJ (Jupiter masses). In addition, we compare here the distributions by projective masses (which is Msin i, where i is the orbital inclination of an exoplanet). For this, the mass distribution of transit exoplanets is transformed into the projective mass distribution. Due to these three changes in the procedure, the obtained RV and transit distributions exhibit a similar behaviour in an interval of M ∈ [0.02, Mmid]MJ and coincide at M ∈ [Mmid, 13]MJ, where Mmid ≈ 0.17MJ

Mobile Airborne Lidar for Remote Methane Monitoring: Design, Simulation of Atmospheric Measurements and First Flight Tests

The results of modernization of a mobile lidar for the airborne monitoring of the methane content in the atmosphere are presented. The modernization was carried out on the basis of in situ tests, several engineering solutions, and preliminary numerical simulations. The in situ tests showed a possibility of sounding background tropospheric methane concentrations along a 500 m surface path. During the modernization, the airborne lidar for methane monitoring was supplemented with an off-axis mirror collimator, which made it possible to reduce the divergence of laser radiation by a factor of 4. The overlapping function was simulated for a biaxial scheme of the mobile lidar with radii of the light-sensitive zone of the receiving optics of 0.1, 0.3, 0.5, 0.8 and 1 mm. The dimensions of the light-sensitive zone were found to provide complete coverage of the field of view of the telescope and a laser beam; the length of the “dead” zone was estimated when a laser beam propagated parallel to the optical axis of the telescope. Airborne methane monitoring in the atmosphere in the informative wavelength range (2916.55–2917 cm−1 on-line and 2915.00 cm−1 off-line) was numerically simulated for midlatitude and Arctic summer. Thus, on the basis of the work carried out, the design of the mobile airborne lidar is substantiated, which is to operate as a part of the Tu-134 “Optik” aircraft laboratory of IAO SB RAS and to perform methane monitoring vertically downwards. The airborne lidar was tested during test flights and the Arctic expedition in 2022. The first experimental results of lidar measurements of the averaged methane concentration vertically downwards from sounding altitudes of 2000–3000, 380, and 270 m were obtained for mid-latitude summer and Arctic summer