Prabhat Sakya

Secretory granule (SG) maturation has been proposed to involve formation of clathrin‐coated vesicles (CCVs) from immature SGs (ISGs). We tested the effect of inhibiting CCV budding by using the clathrin adaptor GGA (Golgi‐associated, γ‐ear‐containing, ADP‐ribosylation factor‐binding protein) on SG maturation in neuroendocrine cells. Overexpression of a truncated, GFP‐tagged GGA, VHS (Vps27, Hrs, Stam)‐GAT (GGA and target of myb (TOM))‐GFP led to retention of MPR, VAMP4, and syntaxin 6 in mature SGs (MSGs), suggesting that CCV budding from ISGs is inhibited by the SG‐localizing VHS‐GAT‐GFP. Furthermore, VHS‐GAT‐GFP‐overexpression disrupts prohormone convertase 2 (PC2) autocatalytic cleavage, processing of secretogranin II to its product p18, and the correlation between PC2 and p18 levels. All these effects were not observed if full‐length GGA1‐GFP was overexpressed. Neither GGA1‐GFP nor VHS‐GAT‐GFP perturbed SG protein budding from the TGN, or homotypic fusion of ISGs. Reducing GGA3 levels by using short interfering (si)RNA also led to VAMP4 retention in SGs, and inhibition of PC2 activity. Our results suggest that inhibition of CCV budding from ISGs downregulates the sorting from the ISGs and perturbs the intragranular activity of PC2.

We have studied the thermotropic and lyotropic phase behaviour of seven monoalkyl glycosides using polarizing microscopy, differential scanning calorimetry and X-ray diffraction. The phase behaviour of these non-ionic surfactants is compared with that of two previously studied monoalkyl glycosides \[1]. We have found that small modifications in chemical structure can lead to large changes in the phase behaviour. The results reveal the effect of changes in alkyl glycoside chemical structure on the phase behaviour, in particular, on the melting point, the clearing point, the solubility in water, and the extent of the lamellar and curved phases. Seven out of the nine surfactants were found to exhibit thermotropic mesomorphism. Furthermore, in the presence of water, three formed lamellar (L), type I cubic (Q) and type I hexagonal (H) phases, two formed lamellar and cubic phases, and two I I formed only lamellar phases. The cubic phase in each case was indexed, either from powderlike or monodomain samples, as spacegroup I a3 d. The lowest order low angle X-ray spacings were found to lie on single, continuous lines with varying water content across the L, Q and H phases, implying epitaxial relationships between these phases at the phase boundaries. I a a I