Effect of lysine succinylation on the regulation of 2-oxoglutarate dehydrogenase inhibitor,OdhI, involved in glutamate production in Corynebacterium glutamicum

In Corynebacterium glutamicum, the activity of the 2-oxoglutarate dehydrogenase (ODH) complex is negatively regulated by the unphosphorylated form of OdhI protein, which is critical for L-glutamate overproduction. We examined the potential impact of protein acylation at lysine (K)-132 of OdhI in C. glutamicum ATCC13032. The K132E succinylation-mimic mutation reduced the ability of OdhI to bind OdhA, the catalytic subunit of the ODH complex, which reduced the inhibition of ODH activity. In vitro succinylation of OdhI protein also reduced the ability to inhibit ODH, and the K132R mutation blocked the effect. These results suggest that succinylation at K132 may attenuate the OdhI function. Consistent with these results, the C. glutamicum mutant strain with OdhI-K132E showed decreased L-glutamate production. Our results indicated that not only phosphorylation but also succinylation of OdhI protein may regulate L-glutamate production in C. glutamicum.     

Neurogenin2‐d4Venus and Gadd45g‐d4Venus transgenic mice: Visualizing mitotic and migratory behaviors of cells committed to the neuronal lineage in the developing mammalian brain

To achieve highly sensitive and comprehensive assessment of the morphology and dynamics of cells committed to the neuronal lineage in mammalian brain primordia, we generated two transgenic mouse lines expressing a destabilized (d4) Venus controlled by regulatory elements of the Neurogenin2 (Neurog2) or Gadd45g gene. In mid‐embryonic neocortical walls, expression of Neurog2‐d4Venus mostly overlapped with that of Neurog2 protein, with a slightly (1 h) delayed onset. Although Neurog2‐d4Venus and Gadd45g‐d4Venus mice exhibited very similar labeling patterns in the ventricular zone (VZ), in Gadd45g‐d4Venus mice cells could be visualized in more basal areas containing fully differentiated neurons, where Neurog2‐d4Venus fluorescence was absent. Time‐lapse monitoring revealed that most d4Venus⁺ cells in the VZ had processes extending to the apical surface; many of these cells eventually retracted their apical process and migrated basally to the subventricular zone, where neurons, as well as the intermediate neurogenic progenitors that undergo terminal neuron‐producing division, could be live‐monitored by d4Venus fluorescence. Some d4Venus⁺ VZ cells instead underwent nuclear migration to the apical surface, where they divided to generate two d4Venus⁺ daughter cells, suggesting that the symmetric terminal division that gives rise to neuron pairs at the apical surface can be reliably live‐monitored. Similar lineage‐committed cells were observed in other developing neural regions including retina, spinal cord, and cerebellum, as well as in regions of the peripheral nervous system such as dorsal root ganglia. These mouse lines will be useful for elucidating the cellular and molecular mechanisms underlying development of the mammalian nervous system.     

Identification of the Neuroblastoma-amplified Gene Product as a Component of the Syntaxin 18 Complex Implicated in Golgi-to-Endoplasmic Reticulum Retrograde Transport

Syntaxin 18, a soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor (SNARE) protein implicated in endoplasmic reticulum (ER) membrane fusion, forms a complex with other SNAREs (BNIP1, p31, and Sec22b) and several peripheral membrane components (Sly1, ZW10, and RINT-1). In the present study, we showed that a peripheral membrane protein encoded by the neuroblastoma-amplified gene (NAG) is a subunit of the syntaxin 18 complex. NAG encodes a protein of 2371 amino acids, which exhibits weak similarity to yeast Dsl3p/Sec39p, an 82-kDa component of the complex containing the yeast syntaxin 18 orthologue Ufe1p. Under conditions favoring SNARE complex disassembly, NAG was released from syntaxin 18 but remained in a p31-ZW10-RINT-1 subcomplex. Binding studies showed that the extreme N-terminal region of p31 is responsible for the interaction with NAG and that the N- and the C-terminal regions of NAG interact with p31 and ZW10-RINT-1, respectively. Knockdown of NAG resulted in a reduction in the expression of p31, confirming their intimate relationship. NAG depletion did not substantially affect Golgi morphology and protein export from the ER, but it caused redistribution of Golgi recycling proteins accompanied by a defect in protein glycosylation. These results together suggest that NAG links between p31 and ZW10-RINT-1 and is involved in Golgi-to-ER transport.     

Recombinant human monoclonal antibodies to human cytomegalovirus glycoprotein B neutralize virus in a complement-dependent manner

Human antibodies specific for HCMV are currently considered as potential anti-HCMV therapeutic agents. In this study, we used a combinatorial human antibody library to isolate and characterize complete human monoclonal antibodies that effectively neutralize HCMV in a complement-dependent manner. One hundred and six clones were isolated in two independent screens using HCMV virions and recombinant glycoprotein B, gB654, as antigens. All of the clones recognized the same molecule gB and were classified into 14 groups based on the amino acid sequence of the V_H region. Seven representative clones from these 14 groups had a strong gB654 binding affinity by surface plasmon resonance (SPR). A pairwise binding competition analysis suggested that there were three groups based on differences in the gB recognition sites. Although Fab fragments of the seven groups showed strong affinity for gB, none of the Fab fragments neutralized HCMV infectivity in vitro. In contrast, complete human IgG₁ antibodies of at least three groups neutralized HCMV in a complement-dependent manner. These data suggest that potent therapeutic antibodies can be obtained from a human antibody library, including most of the functional antibodies that mediate humoral immunity to the selected pathogen.     

Sorting nexin 27 interacts with multidrug resistance-associated protein 4 (MRP4) and mediates internalization of MRP4

Multidrug resistance-associated protein 4 (MRP4/ABCC4) makes a vital contribution to the bodily distribution of drugs and endogenous compounds because of its cellular efflux abilities. However, little is known about the mechanism regulating its cell surface expression. MRP4 has a PDZ-binding motif, which is a potential sequence that modulates the membrane expression of MRP4 via interaction with PDZ adaptor proteins. To investigate this possible relationship, we performed GST pull-down assays and subsequent analysis with matrix-assisted laser desorption/ionization-time of flight mass spectrometry. This method identified sorting nexin 27 (SNX27) as the interacting PDZ adaptor protein with a PDZ-binding motif of MRP4. Its interaction was confirmed by a coimmunoprecipitation study using HEK293 cells. Knockdown of SNX27 by siRNA in HEK293 cells raised MRP4 expression on the plasma membrane, increased the extrusion of 6-[(14)C]mercaptopurine, an MRP4 substrate, and conferred resistance against 6-[(14)C]mercaptopurine. Cell surface biotinylation studies indicated that the inhibition of MRP4 internalization was responsible for these results. Immunocytochemistry and cell surface biotinylation studies using COS-1 cells showed that SNX27 localized to both the early endosome and the plasma membrane. These data suggest that SNX27 interacts with MRP4 near the plasma membrane and promotes endocytosis of MRP4 and thereby negatively regulates its cell surface expression and transport function.