Penicillin-binding protein SpoVD disulphide is a target for StoA in Bacillus subtilis forespores

The bacterial endospore is a dormant and heat-resistant form of life. StoA (SpoIVH) in Bacillus subtilis is a membrane-bound thioredoxin-like protein involved in endospore cortex synthesis. It is proposed to reduce disulphide bonds in hitherto unknown proteins in the intermembrane compartment of developing forespores. Starting with a bioinformatic analysis combined with mutant studies we identified the sporulation-specific, high-molecular-weight, class B penicillin-binding protein SpoVD as a putative target for StoA. We then demonstrate that SpoVD is a membrane-bound protein with two exposed redox-active cysteine residues. Structural modelling of SpoVD, based on the well characterized orthologue PBP2x of Streptococcus pneumoniae , confirmed that a disulphide bond can form close to the active site of the penicillin-binding domain restricting access of enzyme substrate or functional association with other cortex biogenic proteins. Finally, by exploiting combinations of mutations in the spoVD , stoA and ccdA genes in B. subtilis cells, we present strong in vivo evidence that supports the conclusion that StoA functions to specifically break the disulphide bond in the SpoVD protein in the forespore envelope. The findings contribute to our understanding of endospore biogenesis and open a new angle to regulation of cell wall synthesis and penicillin-binding protein activity.     

The chemical character and burial of phosphorus in shallow coastal sediments in the northeastern Baltic Sea

The chemical composition and vertical distribution of sediment phosphorus (P) in shallow coastal sediments of the northeastern Baltic Sea (BS) were characterized by sequential extraction. Different P forms were related to chemical and physical properties of the sediments and the chemistry of pore water and near-bottom water. Sediment P composition varied among the sampling sites located in the Archipelago Sea (AS) and along the northern coast of the Gulf of Finland (GoF): the organic rich sites were high in organic P (OP), while apatite-P dominated in the area affected by sediment transportation. Although the near-bottom water was oxic, the sediments released P. Release of P was most pronounced at the site with high sediment OP and reduced conditions in the sediment-water interface, indicating that P had its origins in organic sources as well as in reducible iron (Fe) oxyhydroxides. The results suggest that even though these coastal areas are shallow enough to lack salinity stratification typical for the brackish BS, they are vulnerable to seasonal oxygen (O₂) depletion and P release because of their patchy bottom topography, which restricts mixing of water. Furthermore, coastal basins accumulate organic matter (OM) and OP, degradation of which further diminishes O₂ and creates the potential for P release from the sediment. In these conditions, an abundance of labile OP may cause marked efflux of P from sediment reserves in the long-term.     

Liver-Fat Accumulation and Insulin Resistance in Obese Women with Previous Gestational Diabetes

Objective: We determined whether fat accumulation in the liver is associated with features of insulin resistance independent of obesity. Research Methods and Procedures: We recruited 27 obese nondiabetic women in whom liver fat (LFAT) content was determined by proton spectroscopy, intra-abdominal and subcutaneous fat by magnetic resonance imaging, and insulin sensitivity by the euglycemic insulin clamp technique. The women were divided based on their median LFAT content (5%) to groups with low (3.2 ± 0.3%) and high (9.8 ± 1.5%) liver fat. The groups were almost identical with respect to age (36 ± 1 vs. 38 ± 1 years in low vs. high-LFAT), body mass index (32.2 ± 0.6 vs. 32.8 ± 0.5 kg/m²), waist-to-hip ratio, intra-abdominal, subcutaneous, and total fat content. Results: Women with high LFAT had features of insulin resistance including higher fasting serum triglyceride (1.93 ± 0.21 vs. 1.11 ± 0.09 mM, p < 0.01) and insulin (14 ± 3 vs. 10 ± 1 mU/L, p < 0.05) concentrations than women with low LFAT. The group with high LFAT also had higher 24-hour blood pressures, and lower whole-body insulin sensitivity compared with the low-LFAT group. Discussion: In obese women with previous gestational diabetes, LFAT, rather than any measure of body composition, is associated with features of insulin resistance.