Bacillus stearothermophilus cell shape determinant gene, mreC and mreD, and their stimulation of protease production in Bacillus subtilis

Co(2+)-dependent gene expression in Streptococcus pneumoniae: opposite effect of Mn(2+) and Co(2+) on the expression of the virulence genes psaBCA, pcpA, and prtA

Manganese (Mn(2+))-, zinc (Zn(2+))- and copper (Cu(2+)) play significant roles in transcriptional gene regulation, physiology, and virulence of Streptococcus pneumoniae. So far, the effect of the important transition metal ion cobalt (Co(2+)) on gene expression of S. pneumoniae has not yet been explored. Here, we study the impact of Co(2+) stress on the transcriptome of S. pneumoniae strain D39. BLAST searches revealed that the genome of S. pneumoniae encodes a putative Co(2+)-transport operon (cbi operon), the expression of which we show here to be induced by a high Co(2+) concentration. Furthermore, we found that Co(2+), as has been shown previously for Zn(2+), can cause derepression of the genes of the PsaR virulence regulon, encoding the Mn(2+)-uptake system PsaBCA, the choline binding protein PcpA and the cell-wall associated serine protease PrtA. Interestingly, although Mn(2+) represses expression of the PsaR regulon and Co(2+) leads to derepression, both metal ions stimulate interaction of PsaR with its target promoters. These data will be discussed in the light of previous studies on similar metal-responsive transcriptional regulators.

High-resolution Structure of the Major Periplasmic Domain from the Cell Shape-determining Filament MreC

Bacterial cell shape is dictated by the cell wall, a plastic structure that must adapt to growth and division whilst retaining its function as a selectively permeable barrier. The modulation of cell wall structure is achieved by a variety of enzymatic functions, all of which must be spatially regulated in a precise manner. The membrane-spanning essential protein MreC has been identified as the central hub in this process, linking the bacterial cytoskeleton to a variety of cell wall-modifying enzymes. Additionally, MreC can form filaments, believed to run perpendicularly to the membrane. We present here the 1.2 A resolution crystal structure of the major periplasmic domain of Streptococcus pneumoniae MreC. The protein shows a novel arrangement of two barrel-shaped domains, one of which shows homology to a known protein oligomerization motif, with the other resembling a catalytic domain from a bacterial protease. We discuss the implications of these results for MreC function, and detail the structural features of the molecule that may be responsible for the binding of partner proteins.

Overexpression and characterization of thermostable serine protease in Escherichia coli encoded by the ORF TTE0824 from Thermoanaerobacter tengcongensis

A novel extracellular serine protease derived from Thermoanaerobacter tengcongensis, designated tengconlysin, was successfully overexpressed in Escherichia coli as a soluble protein by recombination of an N-terminal Pel B leader sequence instead of the original presequence and C-terminal 6x histidine tags. The purified protein was activated by 0.1% sodium dodecyl sulfate (SDS) treatment but not by thermal treatment. The molecular weight of tengconlysin estimated by SDS-polyacrylamide gel electrophoresis analysis and gel filtration chromatography was 37.9 and 36.2 kDa, respectively, suggesting that the enzyme is monomeric. The N-terminal sequence of mature tengconlysin was LDTAT, suggesting that it is a preproprotein containing a 29 amino acid presequence (predicted from the SigP program) and a 117 amino acid prosequence in the N-terminus. The C-terminal putative propeptide (position 469-540 in the preproprotein) did not inhibit the protease activity. The optimum temperature for tengconlysin activity was 90 degrees C in the presence of 1 mM calcium ions and the optimum pH ranged from 6.5 to 7.0. Activity inhibition studies suggest that the protease is a serine protease. The protease was stable in 0.1% SDS and 1-4 M urea at 70 degrees C in the presence of calcium ions and was activated by the denaturing agents.

Mutational effect for stability in a conserved region of thermolysin

AIMS

To investigate the mutational effect for the stability of thermolysin (TLN) in conserved regions.

METHODS AND RESULTS

Mutational effects for stability at autodegradation sites of TLN in conserved region were studied. The bands of mutant TLN (34 kDa) on SDS-PAGE were decreased. However, those of mutant TLN cultivated with CaCl2 recovered to the same level as WT TLN. Dialysis study shows that these mutant TLN require more calcium ions than WT TLN.

CONCLUSIONS

From these results, calcium affinity of mutant TLN in the conserved regions seem to become weak, subsequently mutant TLN were easily autodegraded in the case of low concentration of CaCl2.

SIGNIFICANCE AND IMPACT OF THE STUDY

The autodegradation sites located in conserved regions of bacilli neutral proteases are important for the tertiary structure formation concerning the stability of the protein.

Essential nature of the mreC determinant of Bacillus subtilis

The mre genes of Escherichia coli and Bacillus subtilis are cell shape determination genes. Mutants affected in mre function are spheres instead of the normal rods. Although the mre determinants are not required for viability in E. coli, the mreB determinant is an essential gene in B. subtilis. Conflicting results have been reported as to whether the two membrane-associated proteins MreC and MreD are essential proteins. Furthermore, although the MreB protein has been studied in some detail, the roles of the MreC and MreD proteins in cell shape determination are unknown. We constructed a strain of B. subtilis in which expression of the mreC determinant is dependent upon the addition of isopropyl-beta-D-thiogalactopyranoside to the culture medium. Utilizing this conditional strain, it was shown that mreC is an essential gene in B. subtilis. Furthermore, it was shown that cells lacking sufficient quantities of MreC undergo morphological changes, namely, swelling and twisting of the cells, which is followed by cell lysis. Electron microscopy was utilized to demonstrate that a polymeric material accumulated at one side of the division septum of the cells and that the presence of this material correlated with the bending of the cell. The best explanation for the results is that the MreC protein is involved in the control of septal versus long-axis peptidoglycan synthesis, that cells lacking MreC perform aberrant septal peptidoglycan synthesis, and that lysis results from a deficiency in long-axis peptidoglycan synthesis.