Tension Enhances the Binding Affinity of β1 Integrin by Clamping Talin Tightly: An Insight from Steered Molecular Dynamics Simulations

Integrin activation is a predominant step for cell–cell and cell–ECM interactions. Talin and Kindlin are mechanosensitive adaptor proteins that bind to the integrin cytoplasmic tail and mediate integrin activation, cytoskeleton rearrangement, and focal adhesion assembly. However, knowledge about how Talin and Kindlin synergistically assist integrin activation remains unclear. Here, we performed so-called “ramp-clamp” SMD simulations, which modeled the mechanosignaling from Kindlin, to investigate the effect of tension on the interaction of the β1 integrin cytoplasmic tail with the Talin-F3 domain. The present results showed that mild but not excessive stretching enhanced the binding of integrin with Talin. This mechanical regulation on integrin affinity to Talin referred to an event cascade, in which under stretching, the integrin cytoplasmic tail adopted allostery in response to the mechanical stimulus, remodeling of integrin in favor of Talin-association ensued, and finally, a stable, close-knit complex was formed. In the cascade, the torsion angle transition of integrin was the cue for the stable interaction of the complex under tensile force. The present work suggested a model for Talin and Kindlin to synergistically activate integrin. It should help understand integrin activation and its mechanochemical regulation mechanism, integrin-related innate cellular immune responses, cell adhesion, cell–cell interaction, and integrin-related drug development

Folate-Conjugated Fe₃O₄@SiO₂ Hollow Mesoporous Spheres for Targeted Anticancer Drug Delivery

Herein we developed a targeted anticancer drug delivery system based on folate-conjugated rattle-type Fe3O4@SiO2 hollow mesoporous spheres combining receptor-mediated targeting and magnetic targeting. Folic acid (FA) ligands were successfully grafted onto rattle-type Fe3O4@SiO2 hollow mesoporous spheres via amide reaction. The magnetization saturation value of folate-conjugated Fe3O4@SiO2 spheres (Fe3O4@SiO2−FA) was about 1.6 emu/g, and these spheres could be targeted under an external magnetic field. On the other hand, in vitro cytotoxicity and cell uptake of these Fe3O4@SiO2−FA spheres to Hela cells were evaluated. These Fe3O4@SiO2−FA spheres were nontoxic up to a concentration of 150 μg/mL, and further can be specifically taken up by Hela cells via FA receptor-mediated endocytosis. Doxorubicin hydrochloride (DOX), an anticancer drug, was introduced into Fe3O4@SiO2−FA spheres. The release of DOX from Fe3O4@SiO2−FA spheres had a sustained release pattern, and the DOX-loaded Fe3O4@SiO2−FA spheres exhibited greater cytotoxicity than free DOX and DOX-loaded Fe3O4@SiO2 spheres due to the increase of cell uptake of anticancer drug delivery vehicles mediated by the FA receptor. Therefore, we conclude that folate-conjugated Fe3O4@SiO2 hollow mesoporous spheres have potential for targeted anticancer drug delivery for cancer therapy

Additional file 3 of Under pressure: design and validation of a pressure-sensitive insole for ankle plantar flexion biofeedback during neuromuscular gait training

Additional file 3. Individual knee and ankle joint angles for baseline, plantar pressure biofeedback, and EMG biofeedback walking conditions

Additional file 2 of Under pressure: design and validation of a pressure-sensitive insole for ankle plantar flexion biofeedback during neuromuscular gait training

Additional file 2. Individual medial gastrocnemius activation curves for baseline, plantar pressure biofeedback, and EMG biofeedback walking conditions

Real-Time Study of Graphene’s Phase Transition in Polymer Matrices

We present real-time study of pristine graphene sandwiched in a homogeneous polymer matrix and its phase transition where the graphene membrane irreversibly scrolls and folds above the polymer’s glass temperature. Tubular structures tend to form by curling up from edge defects of graphene and roll along its surface. A single-layer can also fold into two- or three-layer stacks and the overlapping between layers extends along the membrane surface to enlarge up to micrometer sizes. Further, oxidized graphene does not show such reactivity at even higher temperatures, indicating that the intrinsic thermal instability of pristine graphene in the polymer matrix is the origin of the transition

Real-Time Study of Graphene’s Phase Transition in Polymer Matrices

We present real-time study of pristine graphene sandwiched in a homogeneous polymer matrix and its phase transition where the graphene membrane irreversibly scrolls and folds above the polymer’s glass temperature. Tubular structures tend to form by curling up from edge defects of graphene and roll along its surface. A single-layer can also fold into two- or three-layer stacks and the overlapping between layers extends along the membrane surface to enlarge up to micrometer sizes. Further, oxidized graphene does not show such reactivity at even higher temperatures, indicating that the intrinsic thermal instability of pristine graphene in the polymer matrix is the origin of the transition

Additional file 1 of Under pressure: design and validation of a pressure-sensitive insole for ankle plantar flexion biofeedback during neuromuscular gait training

Additional file 1. Individual soleus activation curves for baseline, plantar pressure biofeedback, and EMG biofeedback walking conditions

Mapping Paratope on Antithrombotic Antibody 6B4 to Epitope on Platelet Glycoprotein Ibalpha via Molecular Dynamic Simulations

<div><p>Binding of platelet receptor glycoprotein Ibα (GPIbα) to the A1 domain of von Willebrand factor (vWF) is a critical step in both physiologic hemostasis and pathologic thrombosis, for initiating platelet adhesion to subendothelium of blood vessels at sites of vascular injury. Gain-of-function mutations in GPIbα contribute to an abnormally high-affinity binding of platelets to vWF and can lead to thrombosis, an accurate complication causing heart attack and stroke. Of various antithrombotic monoclonal antibodies (mAbs) targeting human GPIbα, 6B4 is a potent one to inhibit the interaction between GPIbα and vWF-A1 under static and flow conditions. Mapping paratope to epitope with mutagenesis experiments, a traditional route in researches of these antithrombotic mAbs, is usually expensive and time-consuming. Here, we suggested a novel computational procedure, which combines with homology modeling, rigid body docking, free and steered molecular dynamics (MD) simulations, to identify key paratope residues on 6B4 and their partners on GPIbα, with hypothesis that the stable hydrogen bonds and salt bridges are the important linkers between paratope and epitope residues. Based on a best constructed model of 6B4 bound with GPIbα, the survival ratios and rupture times of all detected hydrogen bonds and salt bridges in binding site were examined via free and steered MD simulations and regarded as indices of thermal and mechanical stabilizations of the bonds, respectively. Five principal paratope residues with their partners were predicted with their high survival ratios and/or long rupture times of involved hydrogen bonds, or with their hydrogen bond stabilization indices ranked in top 5. Exciting, the present results were in good agreement with previous mutagenesis experiment data, meaning a wide application prospect of our novel computational procedure on researches of molecular of basis of ligand-receptor interactions, various antithrombotic mAbs and other antibodies as well as theoretically design of biomolecular drugs.</p> </div

Time courses of interatomic distances of six representative bonds in binding site of 6B4/GPIbα complex.

<p>The interatomic distances of six representative bonds were plotted against simulation time, where the interatomic distances were from the oxygen atoms of acidic residues and their respective partners, the nitrogen atoms of basic residues, for three salt bridges, 5^th (A), 4^th (B) and 9^th (C) bonds, or from doners to their respective acceptors for three hydrogen bonds, 16^th (D), 10^th (E) and 1^st (F) bonds. The salt bridges and hydrogen bonds were simulated with the initial conformation I (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042263#pone-0042263-g003" target="_blank">Fig. 3 A</a>) and II (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042263#pone-0042263-g003" target="_blank">Fig. 3 B</a>), respectively. The gray dashed line expresses the distance cut-off of 0.35 nm beyond which the bonds breaks, and the blue, green and red lines exhibit the variation of interatomic distances (nm) of a bond against simulation time (ns) for thrice-repeat independent free MD simulations, respectively. The thermal stabilizations of the 4^th and 10^th bonds (B and E) seemed to be higher than those of the 5^th and 16^th bonds but lower than those of the 9^th and 1^st bonds. Remarkable difference in the thrice-repeat independent simulations showed a random behavior of intermolecular interactions.</p