Cloning of the pelA gene from Bacillus licheniformis 14A and biochemical characterization of recombinant, thermostable, high-alkaline pectate lyase

The pectate lyase gene pelA from alkaliphilic Bacillus licheniformis strain 14A was cloned and sequenced. The nucleotide sequence corresponded to an open reading frame of 1,026 bp that codes for a 39 amino acid signal peptide and a mature protein with a molecular mass of 33,451 Da. The mature PelA showed significant homology to other pectate lyases belonging to polysaccharide lyase family 1, such as enzymes from different Bacillus spp. and Erwinia chrysanthemi. The pelA gene was expressed in Escherichia coli as a recombinant fusion protein containing a C-terminal His-tag, allowing purification to near homogeneity in a one-step procedure. The values for the kinetic parameters K(m) and Vmax of the fusion protein were 0.56 g/l and 51 micromol/min, respectively. The activity of purified PelAHis was inhibited in the presence of excess substrate. Characterization of product formation revealed unsaturated trigalacturonate as the main product. The yields of unsaturated trigalacturonic acids were further examined for the substrates polygalacturonic acid, citrus pectin and sugar-beet pectin.

Use of the pre-pro part of Staphylococcus hyicus lipase as a carrier for secretion of Escherichia coli outer membrane protein A (OmpA) prevents proteolytic degradation of OmpA by cell-associated protease(s) in two different gram-positive bacteria

Heterologous protein secretion was studied in the gram-positive bacteria Bacillus subtilis and Staphylococcus carnosus by using the Escherichia coli outer membrane protein OmpA as a model protein. The OmpA protein was found to be translocated across the plasma membrane of both microorganisms. However, the majority of the translocated OmpA was similarly degraded in B. subtilis and S. carnosus despite the fact that the latter organism does not secrete soluble exoproteases into the culture medium. The finding that purified OmpA, which was added externally to the culture medium of growing S. carnosus cells, remained intact indicates that newly synthesized and exported OmpA is degraded by one or more cell-associated proteases rather than by a soluble exoprotease. Fusion of the mature part of OmpA to the pre-pro part of a lipase from Staphylococcus hyicus allowed the efficient release of the corresponding propeptide-OmpA hybrid protein into the supernatant and completely prevented the cell-associated proteolytic degradation of the mature OmpA, most likely reflecting an important function of the propeptide during secretion of its natural mature lipase moiety. The relevance of our findings for the biotechnological use of gram-positive bacteria as host organisms for the secretory production of heterologous proteins is discussed.

Functional characterization of the Staphylococcus carnosus SecA protein in Escherichia coli and Bacillus subtilis secA mutant strains

The Staphylococcus carnosus secA gene was cloned using the Bacillus subtilis secA gene as a probe. The S. carnosus secA encodes a polypeptide of 844 amino acid residues which is homologous to other known SecA proteins. The S. carnosus SecA functionally complemented the growth and secretion defects of a temperature-sensitive B. subtilis secA mutant at the non-permissive temperature. In contrast, the growth defect of an Escherichia coli secA mutant could not be complemented by the S. carnosus SecA protein. Our results suggest that the interactions of SecA with precursor proteins and/or other components of bacterial preprotein translocase are optimized within each organism.

A cell-free protein translocation system prepared entirely from a gram-positive organism

A cell-free protein translocation system derived exclusively from a Gram-positive bacterium is described here for the first time. Highly efficient in vitro synthesis of plasmid encoded preprolipase of Staphylococcus hyicus is accomplished by coupled transcription/translation using either a cytosolic extract of S. carnosus alone or in combination with T7-RNA-polymerase. Addition of inside-out cytoplasmic membrane vesicles of S. carnosus leads to the partial conversion (processing) of preprolipase to prolipase. In addition, as shown in a protease protection assay, a significant part of preprolipase plus prolipase is translocated in vitro into the lumen of the vesicles. Translocation of preprolipase into the membrane vesicles requires the proton-motive force and the S. carnosus SecA protein.

The Staphylococcus carnosus secE gene: cloning, nucleotide sequence, and functional characterization in Escherichia coli secE mutant strains

A DNA fragment containing the genes secE, nusG and rplK of Staphylococcus carnsosus was cloned using the Escherichia coli rplK gene as a probe. The S. carnosus secE homologue encodes a protein of 65 amino acid residues which is homologous to the carboxyl-terminal region of the E. coli SecE protein. The S. carnosus SecE polypeptide which, in contrast to the E. coli SecE protein, contains only one putative transmembrane segment, could fully replace the E. coli SecE protein in two different secE mutants. These results strongly suggest that the identified secE gene encodes an important component of the S. carnosus protein export apparatus.

An outer membrane protein (OmpA) of Escherichia coli can be translocated across the cytoplasmic membrane of Bacillus subtilis

The translocation of secretory proteins derived from a Gram-positive (Staphylococcus hyicus prolipase) or a Gram-negative (Escherichia coli pre-OmpA protein) bacterium across the cytoplasmic membrane was studied in E. coli and Bacillus subtilis. In both microorganisms, the prolipase was found to be secreted across the plasma membrane when either the pre-prolipase signal peptide (38 amino acids in length) or the pre-OmpA signal peptide (21 amino acids in length) was used. Expression of the gene encoding the authentic pre-OmpA protein in B. subtilis resulted in the translocation of mature OmpA protein across the plasma membrane. Processing of the OmpA precursor in B. subtilis required the electrochemical potential and was sensitive to sodium azide, suggesting that the B. subtilis SecA homologue was involved in the translocation process. The mature OmpA protein, which was most likely present in an aggregated state, was fully accessible to proteases in protoplasted cells. Therefore, our results clearly demonstrate that an outer membrane protein can be secreted by B. subtilis, supporting the notion that the basic mechanism of protein translocation is highly conserved in Gram-positive and Gram-negative bacteria.

The relation between constitutional skin color and photosensitivity estimated from UV-induced erythema and pigmentation dose-response curves

In 54 healthy volunteers we assessed predictors of sensitivity to ultraviolet (UV) light, including Fitzpatrick's sun reactive skin types and constitutional skin color, and compared these with one another and with responses of the skin to UV irradiation, as determined experimentally by a minimal erythema dose (MED), a minimal melanogenic dose (MMD), and dose-response curves for UV-induced erythema and pigmentation. For these studies, a xenon arc solar simulator was used as the source of UV irradiation, and a chromameter interfaced with a computer for objective measurement of UV-induced erythema and pigmentation was employed. The skin type did not correspond well to the constitutional skin color, as measured by a chromameter prior to UV irradiation. Within each skin type, there were large ranges of MED and MMD values and great variability in the shapes of the dose-response curves. Constitutional skin color was also not a good predictor of the measured MED and MMD values but did appear to correlate with the steepness of the dose-response curves for erythema and for pigmentation. From these studies, we propose that objectively measured constitutional skin color is a better predictor of UV responses of the skin than skin type and that steepness of dose-response curves for erythema is a better measure of the response of the skin to UV irradiation than is a MED measurement.