Characterization of a Novel GPI-anchored Protein, a Component of Sphingomyelin-enriched Microdomains at the Golgi Complex

The Golgi complex is the central station along the secretory pathway to sort proteins and lipids to their final destinations. It exists of a series of flattened cisternal membranes that are aligned in parallel to form polarized stacks. This structure is actively maintained amid a large flow of biosynthetic transports through the organelle. Cytosolic oriented Golgi-associated proteins including matrix proteins and a spectrin/ankyrin framework have been identified that may coordinate or maintain the Golgi architecture. Posttranslational modification of these proteins such as occurring during mitosis or apoptosis results in fragmentation of the Golgi complex and demonstrates the dynamic properties of this organelle. The Golgi complex is also a platform to integrate different signaling cascades, which may regulate the unique structure of the Golgi complex. Recently, Golgi-derived lipid rafts were isolated. At the plasma membrane, lipid rafts are considered to play an important role in the coordination of signal transduction processes. Characterization of the protein components of Golgi-derived lipid rafts revealed the distinct identity of these microdomains at the Golgi complex rather than being the precursors of lipid rafts at the plasma membrane. Described in this thesis is a novel protein component of these microdomains. By use of degenerate PCR, combined with phage display, the complete coding sequence of this protein was cloned. Its primary structure and subsequent characterizations show that it is GPI-anchored and therefore a luminal protein. It is a Golgi resident protein and has a Brefeldin A-sensitive Golgi localization. Therefore, this protein was annotated GREG for Golgi-resident GPI-anchored protein. Mapping the Golgi-targeting signal in GREG shows a requirement of the EQ tandem repeat for its Golgi localization. Inhibition of GREG expression by double-strand RNA-mediated interference (dsRNAi) reveals an essential role for GREG in maintenance of the Golgi integrity. Expression of GPI anchor-deficient GREG mutant proteins results in vesiculation of the Golgi complex. These results imply the involvement of a luminal protein in maintenance of the Golgi structure

Detectable MeV neutrinos from black hole neutrino-dominated accretion flows

Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes (BHs) have been theorized as the central engine of relativistic jets launched in massive star core collapse events or compact star mergers. In this work, we calculate the electron neutrino/anti-neutrino spectra of NDAFs by fully taking into account the general relativistic effects, and investigate the effects of viewing angle, BH spin, and mass accretion rate on the results. We show that even though a typical NDAF has a neutrino luminosity lower than that of a typical supernova (SN), it can reach $10^{50}-10^{51}~{\rm erg~s^{-1}}$ peaking at $\sim 10$ MeV, making them potentially detectable with the upcoming sensitive MeV neutrino detectors if they are close enough to Earth. Based on the observed GRB event rate in the local universe and requiring that at least 3 neutrinos are detected to claim a detection, we estimate a detection rate up to $\sim$ (0.10-0.25) per century for GRB-related NDAFs by the Hyper-Kamiokande (Hyper-K) detector if one neglects neutrino oscillation. If one assumes that all Type Ib/c SNe have an engine-driven NDAF, the Hyper-K detection rate would be $\sim$ (1-3) per century. By considering neutrino oscillations, the detection rate may decrease by a factor of 2-3. Detecting one such event would establish the observational evidence of NDAFs in the universe.Comment: 7 pages, 2 figures, 2 tables, accepted for publication in PR

Comment on " a unified scheme for flavored mesons and baryons"

We would comment on the results of the paper "a unified scheme for flavored mesons and baryons" (P.C.Vinodkumar, J.N.Panandya, V.M.Bannur, and S.B.Khadkikar Eur. Phys. J. A4(1999)83), and point out some inconsistencies and mistakes in the work for solving the Dirac equation. In terms of an example for a single particle we investigate the reliability of the perturbative method for computing the Coulomb energy and discuss the contribution to the wavefunction at origin from the Coulomb potential. We conclude that the accuracy of their numerical results needs to be reconsidered.Comment: Latex file, 11page