The Bacillus subtilis YkuV is a thiol:disulfide oxidoreductase revealed by its redox structures and activity

The Bacillus subtilis YkuV responds to environmental oxidative stress and plays an important role for the bacteria to adapt to the environment. Bioinformatic analysis suggests that YkuV is a homolog of membrane-anchored proteins and belongs to the thioredoxin-like protein superfamily containing the typical Cys-Xaa-Xaa-Cys active motif. However, the biological function of this protein remains unknown thus far. In order to elucidate the biological function, we have determined the solution structures of both the oxidized and reduced forms of B. subtilis YkuV by NMR spectroscopy and performed biochemical studies. Our results demonstrated that the reduced YkuV has a low midpoint redox potential, allowing it to reduce a variety of protein substrates. The overall structures of both oxidized and reduced forms are similar, with a typical thioredoxin-like fold. However, significant conformational changes in the Cys-Xaa-Xaa-Cys active motif of the tertiary structures are observed between the two forms. In addition, the backbone dynamics provide further insights in understanding the strong redox potential of the reduced YkuV. Furthermore, we demonstrated that YkuV is able to reduce different protein substrates in vitro. Together, our results clearly established that YkuV may function as a general thiol:disulfide oxidoreductase, which acts as an alternative for thioredoxin or thioredoxin reductase to maintain the reducing environment in the cell cytoplasm.     

Identification of a novel human granzyme B inhibitor secreted by cultured sertoli cells

Sertoli cells have long since been recognized for their ability to suppress the immune system and protect themselves as well as other cell types from harmful immune reaction. However, the exact mechanism or product produced by Sertoli cells that affords this immunoprotection has never been fully elucidated. We examined the effect of mouse Sertoli cell-conditioned medium on human granzyme B-mediated killing and found that there was an inhibitory effect. We subsequently found that a factor secreted by Sertoli cells inhibited killing through the inhibition of granzyme B enzymatic activity. SDS-PAGE analysis revealed that this factor formed an SDS-insoluble complex with granzyme B. Immunoprecipitation and mass spectroscopic analysis of the complex identified a proteinase inhibitor, serpina3n, as a novel inhibitor of human granzyme B. We cloned serpina3n cDNA, expressed it in Jurkat cells, and confirmed its inhibitory action on granzyme B activity. Our studies have led to the discovery of a new inhibitor of granzyme B and have uncovered a new mechanism used by Sertoli cells for immunoprotection.     

Genome sequence of Lactobacillus rhamnosus ATCC 8530

Lactobacillus rhamnosus is found in the human gastrointestinal tract and is important for probiotics. We became interested in L. rhamnosus isolate ATCC 8530 in relation to beer spoilage and hops resistance. We report here the genome sequence of this isolate, along with a brief comparison to other available L. rhamnosus genome sequences.     

Expression and functional analysis of AtMUS81 in Arabidopsis meiosis reveals a role in the second pathway of crossing-over

Meiotic crossovers/chiasmata, that are required to ensure chromosome disjunction, arise via the class I interference-dependent pathway or via the class II interference-free pathway. The proportions of these two classes vary considerably between different organisms. In Arabidopsis, about 85% of chiasmata are eliminated in Atmsh4 mutants, denoting that these are class I events. In budding and fission yeasts Msh4-independent crossovers arise largely or entirely via a Mus81-dependent pathway. To investigate the origins of the 15% residual (AtMSH4-independent) chiasmata in Arabidopsis we conducted a cytological and molecular analysis of AtMUS81 meiotic expression and function. Although AtMUS81 functions in somatic DNA repair and recombination, it is more highly expressed in reproductive tissues. The protein is abundantly present in early prophase I meiocytes, where it co-localizes, in a double-strand break-dependent manner, with the recombination protein AtRAD51. Despite this, an Atmus81 mutant shows normal growth and has no obvious defects in reproductive development that would indicate meiotic impairment. A cytological analysis confirmed that meiosis was apparently normal in this mutant and its mean chiasma frequency was similar to that of wild-type plants. However, an Atmsh4 / Atmus81 double mutant revealed a significantly reduced mean chiasma frequency (0.85 per cell), compared with an Atmsh4 single mutant (1.25 per cell), from which we conclude that AtMUS81 accounts for some, but not all, of the 15% AtMSH4-independent residual crossovers. It is possible that other genes are responsible for these residual chiasmata. Alternatively the AtMUS81 pathway coexists with an alternative parallel pathway that can perform the same functions.     

Male-biased sex ratios in broods of the cooperatively breeding bell miner Manorina melanophrys

We examined the sex ratios of adults and nestlings in the cooperatively breeding bell miner Manorina melanophrys . Males were over-represented among helpers (mean of 6.8 male helpers per nest compared to 0.3 female helpers). 58% of nestlings sampled were identified as male using a molecular genetic marker. This was a significant departure from parity, yet the magnitude of the bias varied between years. The beneficial and male-biased nature of helping behaviour in this species and the similar size of male and female nestlings suggest the net cost of raising males is lower than the cost of raising females. Consequently, the male-biased sex ratio of nestlings we observed is consistent with the predictions of the repayment hypothesis that females may bias the production of their young towards the more helpful sex. Difficulties of generating quantitative predictions from repayment models that can be tested in the field are discussed.