Alina Taylor

Degradation by proteases Lon, Clp and HtrA, of Escherichia coli proteins aggregated in vivo by heat shock; HtrA protease action in vivo and in vitro.

Thermally aggregated, endogenous proteins of Escheri‐chia coli form a distinct fraction, denoted S, which is separable by sucrose‐density‐gradient centrifugation. It was shown earlier that DnaK, DnaJ, IbpA and IbpB heat‐shock proteins are associated with the S fraction. Comparison of the rise and decay of the S fraction in mutants defective for heat‐shock proteases Lon (La), Clp, HtrA (DegP, Do) and in wild‐type strains made studies of proteolysis and the function of the heat‐shock response possible in vivo. Different timing and the extent of action of particular proteases was revealed by the initial size and decay kinetics of the S fraction. The proteases Lon, Clp, and HtrA all participated in removal of the aggregated proteins. Mutation in the gene encoding ClpB caused the most prominent effect (47% stabilization of the S fraction). The correlation between the disappearance of the S fraction and proteolytic activity was supported by the result of the in vitro reaction. Approximately one third of the isolated S fraction was converted to trichloroacetic acid‐soluble products by the purified HtrA protease. Mg2+ ions stimulated the reaction, in contrast to the reaction of the HtrA protease with casein. The digestion of the aggregated proteins, unlike the digestion of casein, by HtrA protease in vitro was inhibited by added DnaJ, which might reflect protection of the aggregated proteins in vivo by DnaJ from excessive degradation. One might expect that such an activity of DnaJ would promote denatured protein renaturation versus proteolysis. Moreover, among the aggregated proteins that are discernible by electrophoresis, none could be identified as being more susceptible than any other to HtrA degradation. The separation pattern of these proteins before and after the in vitro digestion did not show a difference corresponding to the loss of about 30% of constituting proteins. This was interpreted as recognition by the HtrA protease of a state of protein denaturation rather than specific amino acid sequences in particular proteins. We conclude that the fraction consisting of proteins heat‐ aggregated in vivo (i.e. the S fraction) contains endogenous substrates for the heat‐shock proteases tested. Their use for in vitro reaction reveals information that is in some respects different from that obtained with exogenous substrates such as casein.

The R gene product of bacteriophage λ is the murein transglycosylase

SummaryThe radioactively labeled proteins synthesised in Escherichia coli minicells infected by bacteriophage λR and λR+ were compared by polyacrylamide gel electrophoresis. λR mutants, which have lost the ability to lyse host cells, lack a polypeptide of molecular weight 17.5 kD corresponding to the molecular weight of murein transglycosylase — a bacteriolytic enzyme from λ lysates which we have described previously. It has been shown by direct comparison using radio-labeled enzyme that transglycosylase comigrates with the R gene product. The enzyme was endetectable in induced cultures of E. coli W3350 suo (λcI857 Ram5) and C600 (λcI857 acR301), while it was present in a λR−+mutant lysate. We conclude that the transglycosylase is the R gene product.

Response of Escherichia coli cell membranes to induction of λc1857 prophage by heat shock

Heat shock induces protein aggregation in Escherichia coli and E. coli (λc1857). The aggregates (S fraction) appear 15 min post‐induction and are separable from membranes by sucrose density‐gradient centrifugation. The S fraction quickly disappears in wild type strains but persists in rpoH mutant with concomitant quick inner membrane destruction. We propose that: (1) the disappearance of the S fraction reflects a rpoH‐dependent processing, (2) the membrane destruction explains the lethality of the rpoH mutation at elevated temperatures; and (3) the protection of the inner membrane integrity is an important physiological function of the heat‐shock response. We assume that the S fraction of aggregated proteins represents the signal inducing the heat‐shock response.

The role of DnaK/DnaJ and GroEL/GroES systems in the removal of endogenous proteins aggregated by heat‐shock from Escherichia coli cells

The submission of Escherichia coli cells to heat‐shock (45°C, 15 min) caused the intracellular aggregation of endogenous proteins. In the wt cells the aggregates (the S fraction) disappeared 10 min after transfer to 37°C. In contrast, the S fraction in the dnaK and dnaJ mutant strains was stable during approximately one generation time (45 min). This demonstrated that neither the renaturation nor the degradation of the denatured proteins was possible in the absence of DnaK and DnaJ. The groEL44 and groES619 mutations stabilised the aggregates to a lesser extent. It was shown by the use of cloned genes, dnaK/dnaJ or groEL/groES, producing the corresponding proteins in about 4‐fold excess, that the appearance of the S fraction in the wt strain resulted from a transiently insufficient supply of the heat‐shock proteins. Overproduction of the GroEL/GroES proteins in dnaK756 or dnaJ259 background prevented the aggregation, however, overproduction of the DnaK/DnaJ proteins did not prevent the aggregation in the groEL44 or groES619 mutant cells although it accelerated the disappearance of the aggregates. The properties of the aggregated proteins are discussed from the point of view of their competence to renaturation/degradation by the heat‐shock system.

The Rz1 gene product of bacteriophage lambda is a lipoprotein localized in the outer membrane of Escherichia coli

The Rz1 gene of bacteriophage lambda is located within the Rz1 lysis gene. It codes for the 6.5-kDa prolipoprotein (Rz1) which undergoes N-terminal signal sequence cleavage and post-translational lipid modification of the N-terminal Cys of the mature protein. Globomycin, the antibiotic which inhibits bacterial signal peptidase II, specific for prolipoproteins containing diacylglyceryl cysteine [Hayashi and Wu, J. Bioenerg. Biomembr. 22 (1990) 451-471] inhibits the N-terminal sequence cleavage of the Rz1 precursor. The mature protein is rich in Pro, which constitutes 25% of its amino acids (aa). Using a computer-predicted, synthetic, 15-aa antigenic determinant of Rz1 polyclonal anti-Rz[46-60] antibodies, were obtained, and employed to localize Rz1 in bacterial fractions. In induced Escherichia coli lambda lysogens Rz1 was found almost exclusively in the outer membrane (OM). In a strain overproducing Rz1 from the pSB54 plasmid, it was distributed in all the fractions, OM, fraction A and inner membrane (IM). Expression of Rz1 from the pSB54 caused enlargement of fraction A, corresponding to the adhesion sites of OM and IM. Such an enlargement was previously observed in induced lambda lysogens, shortly before the onset of lysis.

Murein transglycosylase from phage λ lysate purification and properties

Abstract Lysates of induced E. coli (λ) lysogens contain two enzymes acting on murein: endopeptidase and murein transglycosylase. The transglycosylase was separated from the endopeptidase and purified to homogeneity. Its bacteriolytic activity was 200-fold higher than that of hen egg lysozyme. The bacteriolytic activity of the lysate depends on the presence of the enzyme. The endopeptidase alone does not lyse the cells, but it enhances the extent of lysis. The properties of the transglycosylase (molecular weight 17 500, pH optimum at 6.6, inactivation by Zn2+), show that it is entirely different from the bacterial enzyme of the same specificity described by others. Data are presented, which suggest that this enzyme is the phage λ R-gene product.

Expression of the Rz gene and the overlapping Rz1 reading frame present at the right end of the bacteriophage lambda genome

The Rz lysis gene of bacteriophage lambda was cloned into the expression vectors, pT7-3 and pT7-7. The recombinant plasmids expressed either a protein of an unexpected 6.5-kDa size (pT7-3H and pSB54) or two proteins of 6.5 and 17.2 kDa (pBH21). The 6.5-kDa protein alone did not complement the lysis defect of the lambda Rz mutant; hence, this protein was not the Rz gene product. Complementation observed as a result of pBH21 expression thus can be ascribed to the 17.2-kDa protein, which agrees with the size based on the nucleotide sequence of Rz. The 6.5 kDa is a product of an open reading frame entirely encompassed within the Rz sequence and denoted by us Rz1. Both proteins were detectable only by autoradiography, which may mean that the genes are expressed at low rates. Polyclonal anti-Rz antibodies (Ab) were obtained by rabbit immunization with a synthetic polypeptide corresponding to an antigenic determinant of Rz defined by a computer program. The Ab reacted with the 17.2-kDa protein resulting from pBH21 expression, as well as with the 17.2-kDa protein present in the induced Escherichia coli W3350(lambda cI857Sam7) lysate.

DnaK/DnaJ chaperone system reactivates endogenous E coli thermostable FBP aldolase in vivo and in vitro; the effect is enhanced by GroE heat shock proteins

Abstract Thermally aggregated, endogenous proteins in Escherichia coli cells form the S fraction, which is separable by sucrose density gradient centrifugation. To date, relatively little is known about the mechanisms of elimination of the heat-aggregated proteins from E coli cells and the composition of the S fraction. We have identified several proteins of the S fraction using 2D-gel electrophoresis and microsequencing. A thermostable II class fructose-1,6-bisphosphate aldolase (Fda protein) appeared to be one of numerous proteins of the S fraction. Fda was purified from E coli overproducer strain and used as a model substrate for investigation of the role of Hsps in prevention and repair of thermal denaturation of proteins both in vivo and in vitro. We found that the heat inactivation of Fda was reversible and that its reactivation in vivo and in vitro required mainly the assistance of the DnaK/DnaJ chaperone system. The dnaK756 and dnaJ259 mutations had a negative effect on the reactivation of thermally inactivated Fda. Moreover, we showed that the reactivation process in vitro was enhanced when GroEL/GroES were added together with DnaK/DnaJ. GroEL/GroES alone were inefficient in the resolubilization or reactivation of the heat-aggregated Fda. It is supposed that the denaturation of the thermostable Fda in vivo results rather from a temporary and transient deficit of Hsps than from the direct heat effect.

Conversion of murein to non-reducing fragments by enzymes from phage λ and Vi II lysates

Abstract A preparation of 200-fold purified endopeptidase from phage λ or Vi II lysates contains an enzyme which splits the amino sugar chains of murein into diffusible, but non-reducing products. The main product is a muropeptide CA with the peptide part identical with that of muropeptide C6. The results of borohydride reduction, negative Morgan-Elson test, and resistance to snail N-acetyl-β-glucosaminidase action suggest that amino sugars may be linked by a 1-1 glucosidic bond, though another structure of the amino sugar part of muropeptide CA is not escluded.

The P1 promoter of the Escherichia coli rpoH gene is utilized by σ70-RNAP or σS-RNAP depending on growth phase

The P1 promoter of the Escherichia coli rpoH gene has been known as a sigma(70)-dependent promoter (RNAP). We show here that it is also recognized by sigma(S). The sigma(70) and sigma(S) RNA polymerase subunits direct transcription from the P1 promoter in the exponential and stationary growth phases, respectively, and transcriptional start sites for the two holoenzymes differ by 1 nt. The transcription after heat shock is sigma(70)-dependent. The results are based on (1) sequence analysis that revealed features of promoters responsive to both, sigma(70)- and sigma(S)-RNAP, (2) in vitro transcription experiments verifying that both holoenzymes are able to transcribe the promoter, (3) electron microscopy results indicating that both holoenzymes bind the same site, (4) primer extension test performed with RNA isolated from the wild-type and rpoS mutant strains, demonstrating that transcription from the P1 promoter in the stationary phase is sigma(S)-dependent. These and previous results point to cooperation of sigma(70), sigma(24), sigma(S) and sigma(54) regulons in the expression of the rpoH gene, coding for the main regulator of the stress response, thus rendering it active in a variety of conditions.