Outer membrane protein folding from an energy landscape perspective

The cell envelope is essential for the survival of Gram-negative bacteria. This specialised membrane is densely packed with outer membrane proteins (OMPs), which perform a variety of functions. How OMPs fold into this crowded environment remains an open question. Here, we review current knowledge about OFMP folding mechanisms in vitro and discuss how the need to fold to a stable native state has shaped their folding energy landscapes. We also highlight the role of chaperones and the β-barrel assembly machinery (BAM) in assisting OMP folding in vivo and discuss proposed mechanisms by which this fascinating machinery may catalyse OMP folding

A unified model for BAM function that takes into account type Vc secretion and species differences in BAM composition

Transmembrane proteins in the outer membrane of Gram-negative bacteria are almost exclusively β-barrels. They are inserted into the outer membrane by a conserved and essential protein complex called the BAM (for β-barrel assembly machinery). In this commentary, we summarize current research into the mechanism of this protein complex and how it relates to type V secretion. Type V secretion systems are autotransporters that all contain a β-barrel transmembrane domain inserted by BAM. In type Vc systems, this domain is a homotrimer. We argue that none of the current models are sufficient to explain BAM function particularly regarding type Vc secretion. We also find that current models based on the well-studied model system Escherichia coli mostly ignore the pronounced differences in BAM composition between different bacterial species. We propose a more holistic view on how all OMPs, including autotransporters, are incorporated into the lipid bilayer

Targeting of captopril to the kidney reduces renal angiotensin-converting enzyme activity without affecting systemic blood pressure

We have synthesized a prodrug of the angiotensin-converting enzyme (ACE) inhibitor captopril by coupling this drug covalently to the low molecular weight protein (LMWP) lysozyme. Such drug-LMWP conjugates can be used for renal drug delivery, since LMWPs accumulate specifically in the proximal tubular cells of the kidney. In the present study, we compared the effects of captopril-lysozyme and free captopril in male Wistar rats. ACE activity in plasma and the kidney was measured after intravenous bolus injection of either the captopril-lysozyme conjugate (33 mg . kg(-1), corresponding to 0.2 mg . kg(-1) captopril) or equivalent dosages of free captopril and lysozyme. The administration of the captopril-lysozyme conjugate resulted in less plasma ACE inhibition and a longer-lasting renal ACE inhibition compared with the free drug. Effects on blood pressure and natriuresis were studied during intravenous infusion of captopril-lysozyme (275 mg . kg(-1) . 6 h(-1) conjugate, corresponding to 5 mg . kg(-1) . 6 h(-1) captopril) or an equimolar dosage of free captopril. Captopril-lysozyme did not affect systemic blood pressure, whereas free captopril lowered blood pressure significantly (-23 +/- 32% versus control after 6 h). Captopril-lysozyme increased natriuresis about 3-fold compared with control levels (260 +/- 32% after 6 h), whereas free captopril treatment resulted in a reduced sodium excretion (26 +/- 12%). Furthermore, captopril at a lower dose, which only moderately lowered blood pressure, showed an increased sodium excretion. We conclude that renal delivery of captopril using captopril-lysozyme results in reduced systemic activity and increased kidney-specific activity of the targeted drug

Septal Pore Cap Protein SPC18, Isolated from the Basidiomycetous Fungus Rhizoctonia solani, Also Resides in Pore Plugs▿

The hyphae of filamentous fungi are compartmentalized by septa that have a central pore. The fungal septa and septum-associated structures play an important role in maintaining cellular and intrahyphal homeostasis. The dolipore septa in the higher Basidiomycota (i.e., Agaricomycotina) are associated with septal pore caps. Although the ultrastructure of the septal pore caps has been studied extensively, neither the biochemical composition nor the function of these organelles is known. Here, we report the identification of the glycoprotein SPC18 that was found in the septal pore cap-enriched fraction of the basidiomycetous fungus Rhizoctonia solani. Based on its N-terminal sequence, the SPC18 gene was isolated. SPC18 encodes a protein of 158 amino acid residues, which contains a hydrophobic signal peptide for targeting to the endoplasmic reticulum and has an N-glycosylation motif. Immunolocalization showed that SPC18 is present in the septal pore caps. Surprisingly, we also observed SPC18 being localized in some plugs. The data reported here strongly support the hypothesis that septal pore caps are derived from endoplasmic reticulum and are involved in dolipore plugging and, thus, contribute to hyphal homeostasis in basidiomycetous fungi

Cell wall attachment of a widely distributed peptidoglycan binding domain is hindered by cell wall constituents

The C-terminal region (cA) of the major autolysin AcmA of Lactococcus lactis contains three highly similar repeated regions of 45 amino acid residues (LysM domains), which are separated by nonhomologous sequences. The cA domain could be deleted without destroying the cell wall-hydrolyzing activity of the enzyme in vitro. This AcmA derivative was capable neither of binding to lactococcal cells nor of lysing these cells while separation of the producer cells was incomplete. The cA domain and a chimeric protein consisting of cA fused to the C terminus of MSA2, a malaria parasite surface antigen, bound to lactococcal cells specifically via cA. The fusion protein also bound to many other Gram-positive bacteria. By chemical treatment of purified cell walls of L. lactis and Bacillus subtilis, peptidoglycan was identified as the cell wall component interacting with cA. Immunofluorescence studies showed that binding is on specific locations on the surface of L. lactis, Enterococcus faecalis, Streptococcus thermophilus, B. subtilis, Lactobacillus sake, and Lactobacillus casei cells. Based on these studies, we propose that LysM-type repeats bind to peptidoglycan and that binding is hindered by other cell wall constituents, resulting in localized binding of AcmA. Lipoteichoic acid is a candidate hindering component. For L. lactis SK110, it is shown that lipoteichoic acids are not uniformly distributed over the cell surface and are mainly present at sites where no MSA2cA binding is observed

Labour market institutions and economic performance in the Netherlands

The central question of this article is whether or not effectiveness and efficiency are improved by the stronger reliance on markets given Dutch labour market institutions and their resulting corporatist wage formation. In answering this question, besides the influence on the production costs (neoclassical approach), we explicitly deal with and quantify the 'hidden' transaction costs (institutional economics approach) of more decentralized labour relations, flexibilization of the labour market, and working conditions 'a la carte'. The results presented cast doubt on both the efficiency and the effectiveness of recently introduced tailor-made solutions in the Dutch economy.Corporatism, economic performance, Netherlands, transaction costs,