Legionella hijacks the host Golgi-to-ER retrograde pathway for the association of Legionella-containing vacuole with the ER

Legionella pneumophila (L. pneumophila) is a gram-negative bacterium that replicates in a compartment that resembles the host endoplasmic reticulum (ER). To create its replicative niche, L. pneumophila manipulates host membrane traffic and fusion machineries. Bacterial proteins called Legionella effectors are translocated into the host cytosol and play a crucial role in these processes. In an early stage of infection, Legionella subverts ER-derived vesicles (ERDVs) by manipulating GTPase Rab1 to facilitate remodeling of the Legionella-containing vacuole (LCV). Subsequently, the LCV associates with the ER in a mechanism that remains elusive. In this study, we show that L. pneumophila recruits GTPases Rab33B and Rab6A, which regulate vesicle trafficking from the Golgi to the ER, to the LCV to promote the association of LCV with the ER. We found that recruitment of Rab6A to the LCV depends on Rab33B. Legionella effector SidE family proteins, which phosphoribosyl-ubiquitinate Rab33B, were found to be necessary for the recruitment of Rab33B to the LCV. Immunoprecipitation experiments revealed that L. pneumophila facilitates the interaction of Rab6 with ER-resident SNAREs comprising syntaxin 18, p31, and BNIP1, but not tethering factors including NAG, RINT-1, and ZW10, which are normally required for syntaxin 18-mediated fusion of Golgi-derived vesicles with the ER. Our results identified a Rab33B-Rab6A cascade on the LCV and the interaction of Rab6 with ER-resident SNARE proteins for the association of LCV with the ER and disclosed the unidentified physiological role of SidE family proteins.     

Purification and Characterization of Kynurenine Aminotransferase I from Human Brain

Abstract: Two kynurenine aminotransferases (KATs), arbitrarily termed KAT I and KAT II, are capable of producing the neuroinhibitory brain metabolite kynurenic acid from l -kynurenine in human brain tissue. Here we describe the purification of KAT I to homogeneity and the subsequent characterization of the enzyme using physicochemical, biochemical, and immunological methods. KAT I was purified from human brain ∼2,000-fold with a yield of 2%. Assessed by polyacrylamide gel electrophoresis, KAT I migrated toward the anode as a single protein with a mobility of 0.5. The pure enzyme was found to be a dimer consisting of two identical subunits of ∼60 kDa. Among several oxo acids tested, KAT I showed highest activity with 2-oxoisocaproate. Kinetic analyses of the pure enzyme revealed an absolute K _m of 2.0 m M and 10.0 m M for l -kynurenine and pyruvate, respectively. KAT I activity was substantially inhibited by l -glutamine, l -phenylalanine, and l -tryptophan, using either pyruvate (1 m M ) or 2-oxoisocaproate (1 m M ) as a cosubstrate. l -Tryptophan inhibited enzyme activity noncompetitively with regard to pyruvate ( K _i = 480 µ M ) and competitively with regard to l -kynurenine ( K _i = 200 µ M ). Anti-KAT I antibodies were produced against pure KAT I and were partially purified by conventional techniques. Immunotitration and immunoblotting analyses confirmed that KAT I is clearly distinct from both human KAT II and rat kynurenine-pyruvate aminotransferase. Pure human KAT I and its antibody will serve as valuable tools in future studies of kynurenic acid production in the human brain under physiological and pathological conditions.     

Effects of different light intensities during the forenoon on the afternoon thermal sensation in mild cold

1. 1. The study aimed at knowing whether thermal sensation during afternoon cool exposure could be influenced by bright light (4000 lx) or dim light (200 lx) in the forenoon.

2. 2. The subjects felt cooler after exposure to dim light than to bright light.

3. 3. Melatonin in the urine was significantly higher in bright light than in dim light at 10:30 h and at noon.

     

Response Variance in Functional Maps: Neural Darwinism Revisited

The mechanisms by which functional maps and map plasticity contribute to cortical computation remain controversial. Recent studies have revisited the theory of neural Darwinism to interpret the learning-induced map plasticity and neuronal heterogeneity observed in the cortex. Here, we hypothesize that the Darwinian principle provides a substrate to explain the relationship between neuron heterogeneity and cortical functional maps. We demonstrate in the rat auditory cortex that the degree of response variance is closely correlated with the size of its representational area. Further, we show that the response variance within a given population is altered through training. These results suggest that larger representational areas may help to accommodate heterogeneous populations of neurons. Thus, functional maps and map plasticity are likely to play essential roles in Darwinian computation, serving as effective, but not absolutely necessary, structures to generate diverse response properties within a neural population.