Towards the development of Bacillus subtilis as a cell factory for membrane proteins and protein complexes

Background: The Gram-positive bacterium Bacillus subtilis is an important producer of high quality industrial enzymes and a few eukaryotic proteins. Most of these proteins are secreted into the growth medium, but successful examples of cytoplasmic protein production are also known. Therefore, one may anticipate that the high protein production potential of B. subtilis can be exploited for protein complexes and membrane proteins to facilitate their functional and structural analysis. The high quality of proteins produced with B. subtilis results from the action of cellular quality control systems that efficiently remove misfolded or incompletely synthesized proteins. Paradoxically, cellular quality control systems also represent bottlenecks for the production of various heterologous proteins at significant concentrations. Conclusion: While inactivation of quality control systems has the potential to improve protein production yields, this could be achieved at the expense of product quality. Mechanisms underlying degradation of secretory proteins are nowadays well understood and often controllable. It will therefore be a major challenge for future research to identify and modulate quality control systems of B. subtilis that limit the production of high quality protein complexes and membrane proteins, and to enhance those systems that facilitate assembly of these proteins.

Inactivation of the Ecs ABC Transporter of Staphylococcus aureus Attenuates Virulence by Altering Composition and Function of Bacterial Wall

Peer reviewe

Bacillus subtilis SpoIIIJ and YqjG Function in Membrane Protein Biogenesis

In all domains of life Oxa1p-like proteins are involved in membrane protein biogenesis. Bacillus subtilis, a model organism for gram-positive bacteria, contains two Oxa1p homologs: SpoIIIJ and YqjG. These molecules appear to be mutually exchangeable, although SpoIIIJ is specifically required for spore formation. SpoIIIJ and YqjG have been implicated in a posttranslocational stage of protein secretion. Here we show that the expression of either spoIIIJ or yqjG functionally compensates for the defects in membrane insertion due to YidC depletion in Escherichia coli. Both SpoIIIJ and YqjG complement the function of YidC in SecYEG-dependent and -independent membrane insertion of subunits of the cytochrome o oxidase and F1Fo ATP synthase complexes. Furthermore, SpoIIIJ and YqjG facilitate membrane insertion of F1Fo ATP synthase subunit c from both E. coli and B. subtilis into inner membrane vesicles of E. coli. When isolated from B. subtilis cells, SpoIIIJ and YqjG were found to be associated with the entire F1Fo ATP synthase complex, suggesting that they have a role late in the membrane assembly process. These data demonstrate that the Bacillus Oxa1p homologs have a role in membrane protein biogenesis rather than in protein secretion.

The YidC/Oxa1/Alb3 protein family: common principles and distinct features

The members of the YidC/Oxa1/Alb3 protein family are evolutionary conserved in all three domains of life. They facilitate the insertion of membrane proteins into bacterial, mitochondrial, and thylakoid membranes and have been implicated in membrane protein folding and complex formation. The major classes of substrates are small hydrophobic subunits of large energy-transducing complexes involved in respiration and light capturing. All YidC-like proteins share a conserved membrane region, whereas the N- and C-terminal regions are diverse and fulfill accessory functions in protein targeting.

Bacillus subtilis YqjG is required for genetic competence development

Members of the evolutionary conserved Oxa1/Alb3/YidC family have been shown to play an important role in membrane protein insertion, folding and/or assembly. Bacillus subtilis contains two YidC-like proteins, denoted as SpoIIIJ and YqjG. SpoIIIJ and YqjG are largely exchangeable, but SpoIIIJ is essential for spore formation and YqjG cannot complement this activity. To elucidate the role of YqjG, we determined the membrane proteome and functional aspects of B. subtilis cells devoid of SpoIIIJ, YqjG or both. The data show that SpoIIIJ and YqjG have complementary functions in membrane protein insertion and assembly. The reduced levels of F1FO ATP synthase in cells devoid of both SpoIIIJ and YqjG are due to a defective assembly of the F1-domain onto the F0-domain. Importantly, for the first time, a specific function is demonstrated for YqjG in genetic competence development.

The role of the N-terminal amphipathic helix in bacterial YidC: Insights from functional studies, the crystal structure and molecular dynamics simulations

The evolutionary conserved YidC is a unique dual-function membrane protein that adopts insertase and chaperone conformations. The N-terminal helix of Escherichia coli YidC functions as an uncleaved signal sequence and is important for membrane insertion and interaction with the Sec translocon. Here, we report the first crystal structure of Thermotoga maritima YidC (TmYidC) including the N-terminal amphipathic helix (N-AH) (PDB ID: 6Y86). Molecular dynamics simulations show that N-AH lies on the periplasmic side of the membrane bilayer forming an angle of about 15° with the membrane surface. Our functional studies suggest a role of N-AH for the species-specific interaction with the Sec translocon. The reconstitution data and the superimposition of TmYidC with known YidC structures suggest an active insertase conformation for YidC. Molecular dynamics (MD) simulations of TmYidC provide evidence that N-AH acts as a membrane recognition helix for the YidC insertase and highlight the flexibility of the C1 region underlining its ability to switch between insertase and chaperone conformations. A structure-based model is proposed to rationalize how YidC performs the insertase and chaperone functions by re-positioning of N-AH and the other structural elements

Concomitant endocrine and immune alterations during alcohol intoxication and acute withdrawal in alcohol-dependent subjects

Although both alcohol intoxication and withdrawal have been demonstrated to produce significant endocrine alterations, no data exist on the effects of acute withdrawal on immune functions. Therefore, the current study investigated the effect of alcohol intoxication and acute withdrawal on plasma cortisol, prolactin and catecholamines, and blood leukocyte subset distribution in alcohol-dependent subjects. Nine male alcoholics admitted to the university clinic for alcohol dependence and 9 age-matched controls participated in the study. Blood was drawn from the alcohol-dependent subjects at 10:30 a.m. on day 0 (chronic alcohol intoxication), at the same time during acute alcohol withdrawal (day 1) and following the resolution of acute withdrawal (day 7). Blood was drawn from age- and gender-matched healthy control subjects at the corresponding time points. Plasma was then analyzed for hormone concentrations and blood examined for leukocyte subsets by flow cytometry. Alcohol-dependent patients displayed significantly elevated plasma cortisol during intoxication and withdrawal, which decreased to control levels following resolution of acute withdrawal. Small elevations of plasma prolactin and catecholamines were also observed during intoxication. Furthermore, alcohol-dependent subjects showed reduced absolute numbers of CD4(+) and CD8(+) T cells and natural killer cells compared with healthy controls across all time points. In contrast, although monocyte numbers were lower in alcohol-dependent patients during intoxication, acute alcohol withdrawal increased the number of monocytes in patients. Thus, alcohol dependence produces a general suppression of leukocyte subset populations in blood. However, resolution of acute alcohol withdrawal is associated with a return of plasma cortisol to control levels, and a concomitant increase in peripheral blood monocyte number