Laccase-assisted bio-grafting of polyhydroxy-alkanoates (PHAs) onto the ethyl cellulose (EC) backbone

In the present study, a novel enzyme-based methodology for grafting Polyhydroxyalkanoates (PHAs) onto the ethyl cellulose (EC) as a backbone polymer was developed. Laccase assisted copolymerization was carried out under mild and eco-friendly reaction conditions. The resulting homogeneous composite membranes were characterized by Fourier-transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Atomic Force Microscopy (AFM). The FTIR spectra of pure PHAs and PHAs containing graft composites (PHAs-g-EC) showed their strong characteristic bands at 1721 cm1, 1651 cm-1 and 1603 cm-1 respectively. Other accompanying bands in the range of 900-1300 cm-1 correspond to C=O vibration and C-O-C bond stretching, which could be contributed from PHAs and EC, respectively. The high intensity of the 3358 cm-1 band in the graft composite may have corresponded to the degradation of the carboxylic group from PHAs and also showed an increase of hydrogen-bonded groups at that distinct band region. The morphology was examined by SEM, which showed the well dispersed PHAs crystals in the backbone polymer of EC. XRD pattern for PHAs showed distinct peaks at 2-Theta values of 28o, 32o, 34o, 39o, 46o, 57o, 64o, 78o and 84o that represent the crystalline nature of PHAs. In comparison with those of neat PHAs, the degree of crystallinity for PHAs-g-EC decreased and this reduction is mainly because of the new cross-linking of PHAs within the EC backbone that changes the morphology and destroys the crystallites. Improved mechanical properties were observed for the PHAs-g-EC as compared to the individual components due to the impregnation of EC as reinforcement into the PHAs matrix. Improved mechanical strength enhanced thermal properties, along with low crystallinity of the present PHAs-g-EC suggesting its potential for various industrial and bio-medical applications.

Molecular mechanisms controlling synaptic recruitment of GluA4 subunit-containing AMPAreceptors

Synaptic recruitment of AMPA receptors (AMPARs) represents a key postsynaptic mechanism driving functional development and maturation of glutamatergic synapses. At immature hippocampal synapses, PKA-driven synaptic insertion of GluA4 is the predominant mechanism for synaptic reinforcement. However, the physiological significance and molecular determinants of this developmentally restricted form of plasticity are not known. Here we show that PKA activation leads to insertion of GluA4 to synaptic sites with initially weak or silent AMPAR-mediated transmission. This effect depends on a novel mechanism involving the extreme C-terminal end of GluA4, which interacts with the membrane proximal region of the C-terminal domain to control GluA4 trafficking. In the absence of GluA4, strengthening of AMPAR-mediated transmission during postnatal development was significantly delayed. These data suggest that the GluA4-mediated activation of silent synapses is a critical mechanism facilitating the functional maturation of glutamatergic circuitry during the critical period of experience-dependent fine-tuning.