Background: Binding of Dab2 to sulfatides results in platelet aggregation inhibition. Results: The structure of a Dab2-derived peptide (SBM) embedded in dodecylphosphocholine micelles, characterization of its minimal functional sulfatide-binding site, and its inhibitory platelet aggregation activity were determined. Conclusion: An amphipathic helical region of Dab2 SBM binds sulfatides, leading to platelet aggregation inhibition. Significance: Dab2 SBM may lead to the design of novel aggregatory inhibitors.

The Wnt-dependent, β-catenin-independent pathway modulates cell movement and behavior. A downstream regulator of this signaling pathway is Dishevelled (Dvl), which, among other multiple interactions, binds to the Frizzled receptor and the plasma membrane via phosphatidic acid (PA) in a mechanism proposed to be pH-dependent. While the Dvl DEP domain is central to the β-catenin-independent Wnt signaling function, the mechanism underlying its physical interaction with the membrane remains elusive. In this report, we elucidate the structural and functional basis of PA association to the Dvl2 DEP domain. Nuclear magnetic resonance, molecular-dynamics simulations, and mutagenesis data indicated that the domain interacted with the phospholipid through the basic helix 3 and a contiguous loop with moderate affinity. The association suggested that PA binding promoted local conformational changes in helix 2 and β-strand 4, both of which are compromised to maintain a stable hydrophobic core in the DEP domain. We also show that the Dvl2 DEP domain bound PA in a pH-dependent manner in a mechanism that resembles deprotonation of PA. Collectively, our results structurally define the PA-binding properties of the Dvl2 DEP domain, which can be exploited for the investigation of binding mechanisms of other DEP domain-interacting proteins.

The translationally-controlled tumor protein (TCTP) is a highly conserved, ubiquitously expressed, abundant protein that is broadly distributed among eukaryotes. Its biological function spans numerous cellular processes ranging from regulation of the cell cycle and microtubule stabilization to cell growth, transformation, and death processes. In this work, we propose a new function for TCTP as a “buffer protein” controlling cellular homeostasis. We demonstrate that binding of hemin to TCTP is mediated by a conserved His-containing motif (His76His77) followed by dimerization, an event that involves ligand-mediated conformational changes and that is necessary to trigger TCTP's cytokine-like activity. Mutation in both His residues to Ala prevents hemin from binding and abrogates oligomerization, suggesting that the ligand site localizes at the interface of the oligomer. Unlike heme, binding of Ca2+ ligand to TCTP does not alter its monomeric state; although, Ca2+ is able to destabilize an existing TCTP dimer created by hemin addition. In agreement with TCTP's proposed buffer function, ligand binding occurs at high concentration, allowing the “buffer” condition to be dissociated from TCTP's role as a component of signal transduction mechanisms.

Magnetic drug carrier has been employed in drug delivery for over 30 years. Modern nanotechnology has improved its efficiency dramatically by decreasing its diameter into nanoscale. It may help chemotherapeutic agents penetrate BBB and raise local drug concentration in brain, which is the ideal model for glioma treatment. In our study, magnetic carrier was fabricated with octadecyl quaternized caroxymethyl chitosan (OQCMC), hydrophobic Fe 3 O 4 ferrofluid and cholesterol, which showed a uniform diameter of 20 nm under transmission electronic microscopy and superparamagnetic character in vibration sample magnetical measurement system. To investigate the efficacy of drug delivery, paclitaxel was used as loaded drug and analyzed by the HPLC. Results showed that magnetic carrier released drugs for more than 20 d in vitro and maintain the drug concentration above 0.4 mg/g for 16 h in rat brain after magnetic targeting. Drug concentration increased by 1-3 folds when delivered by carrier without magnetic targeting, and by 3-15 folds after magnetic targeting. Cellular study revealed that the magnetic carrier was clearly localized in the targeted cortex neural cells and U251-MG cell lines. These results showed that this magnetic carrier is capable of maintaining high drug concentration in magnetically targeted area and carrying drugs or genes into cells, which is potentially promising for local chemotherapy to brain tumors.

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