Molecular cloning, expression, and characterization of dnaK in Streptococcus pneumoniae

Expression, Rapid Purification and Functional Analysis of DnaK from Rhodococcus ruber

BACKGROUND

Heat shock proteins (HSPs) represent a group of important proteins which are produced by all kinds of organisms especially under stressful conditions. DnaK, an Hsp70 homolog in prokaryotes, has indispensable roles when microbes was confronted with stress conditions. However, few data on DnaK from Rhodococcus sp. were available in the literature. In a previous study, we reported that toluene and phenol stress gave rise to a 29.87-fold and 3.93-fold increase for the expression of DnaK from R. ruber SD3, respectively. Thus, we deduced DnaK was in correlation with the organic solvent tolerance of R. ruber SD3.

OBJECTIVE

To elucidate the role of DnaK in the organic solvent tolerance of R. ruber SD3, expression, purification and functional analysis of Dnak from R. ruber SD3 were performed in the present paper.

METHODS

In this article, DnaK from R. ruber SD3 was heterologously expressed in E. coli BL21(DE3) and purified by affinity chromatography. Functional analysis of DnaK was performed using determination of kinetics, docking, assay of chaperone activity and microbial growth.

RESULTS

The recombinant DnaK was rapidly purified by affinity chromatography with the purification fold of 1.9 and the recovery rate of 57.9%. Km, Vmax and Kcat for Dnak from R. ruber SD3 were 80.8 μM, 58.1 nmol/min and 374.3 S-1, respectively. The recombinant protein formed trimer in vitro, with the calculated molecular weight of 214 kDa. According to In-silico analysis, DnaK interacted with other molecular chaperones and some important proteins in the metabolism. The specific activity of catalase in the presence of recombinant DnaK was 1.85 times or 2.00 times that in the presence of BSA or Tris-HCl buffer after exposure to 54 °C for 1h. E. coli transformant with pET28-dnak showed higher growth than E. coli transformant with pET28 at 43°C and in the presence of phenol, respectively.

CONCLUSION

The biochemical properties and the interaction analysis of DnaK from R. ruber SD3 deepened our understanding of DnaK function. DnaK played an important role in microbial growth when R. ruber was subjected to various stress such as heating and organic solvent.

Proteomic variation and diversity in clinical Streptococcus pneumoniae isolates from invasive and non-invasive sites

Streptococcus pneumoniae is responsible for a variety of invasive and non-invasive human infections. There are over 90 serotypes of S. pneumoniae differing in their ability to adapt to the different niches within the host. Two-dimensional gel electrophoresis was used to discriminate clinical S. pneumoniae isolates recovered from either blood cultures (invasive site isolates) or other sites, including sputum, tracheal aspirate, ear, eye and skin swabs (non-invasive site isolates). Global protein expression profiles for five invasive site and six non-invasive site isolates representing five different serotypes (serotypes 4, 6, 9, 14 and 23) were obtained for each isolate and combined into a single data set using Progenesis SameSpots^™ software. One-hundred and eighty six protein spots (39% of the protein spots in the dataset) differed significantly (ANOVA, p<0.05) in abundance between the invasive site (101 upregulated protein spots) and non-invasive site (85 upregulated protein spots) isolates. Correlations between the bacterial proteomes and their sites of isolation were determined by Principal Component Analysis (PCA) using the significantly different protein spots. Out of the 186 variable protein spots, 105 exhibited a serotype-associated pattern of variability. The expression of the remaining 81 protein spots was concluded to be uniquely linked to the site of bacterial isolation. Mass spectrometry was used to identify selected protein spots that showed either constant or differential abundance levels. The identified proteins had a diverse range of functions including, capsule biogenesis, DNA repair, protein deglycation, translation, stress response and virulence as well as amino acid, carbohydrate, lipid and nucleotide metabolism. These findings provide insight on the proteins that contribute towards the adaptation of the bacteria to different sites within the host.

Characterization of a mucoid clone of Streptococcus zooepidemicus from an epizootic of equine respiratory disease in New Caledonia

Streptococcus equi subspecies zooepidemicus (Sz) is a tonsillar and mucosal commensal of healthy horses with the potential to cause opportunistic infections of the distal respiratory tract stressed by virus infection, transportation, training or high temperature. The invasive clone varies from horse to horse with little evidence of lateral transmission in the group. Tonsillar isolates are non-mucoid although primary isolates from opportunist lower respiratory tract infections may initially be mucoid. In this study, a novel stably mucoid Sz (SzNC) from a clonal epizootic of respiratory disease in horses in different parts of New Caledonia is described. SzNC (ST-307) was isolated in pure culture from transtracheal aspirates and as heavy growths from 80% of nasal swabs (n=31). Only 4% of swabs from unaffected horses (n=25) yielded colonies of Sz. A viral etiology was ruled out based on culture and early/late serum antibody screening. Evidence for clonality of SzNC included a mucoid colony phenotype, SzP and SzM sequences, and multilocus sequence typing. SzNC, with the exception of isolates at the end of the outbreak, was hyaluronidase positive. Its SzP protein was composed of an N2 terminal, and HV4 variable region motifs and 18 carboxy terminal PEPK repeats. Biotin labeling of surface proteins revealed DnaK and alanyl-tRNA synthetase (AlaS) on the surface of clonal isolates, but not on non-clonal non-mucoid Sz from horses in the epizootic or unrelated US isolates. Reactivity of these proteins and SzP with convalescent serum indicated expression during infection.

Comparative proteomic analysis of Streptococcus suis biofilms and planktonic cells that identified biofilm infection-related immunogenic proteins

Streptococcus suis (SS) is a zoonotic pathogen that causes severe disease symptoms in pigs and humans. Biofilms of SS bind to extracellular matrix proteins in both endothelial and epithelial cells and cause persistent infections. In this study, the differences in the protein expression profiles of SS grown either as planktonic cells or biofilms were identified using comparative proteomic analysis. The results revealed the existence of 13 proteins of varying amounts, among which six were upregulated and seven were downregulated in the Streptococcus biofilm compared with the planktonic controls. The convalescent serum from mini-pig, challenged with SS, was applied in a Western blot assay to visualize all proteins from the biofilm that were grown in vitro and separated by two-dimensional gel electrophoresis. A total of 10 immunoreactive protein spots corresponding to nine unique proteins were identified by MALDI-TOF/TOF-MS. Of these nine proteins, five (Manganese-dependent superoxide dismutase, UDP-N-acetylglucosamine 1-carboxyvinyltransferase, ornithine carbamoyltransferase, phosphoglycerate kinase, Hypothetical protein SSU05_0403) had no previously reported immunogenic properties in SS to our knowledge. The remaining four immunogenic proteins (glyceraldehyde-3-phosphate dehydrogenase, hemolysin, pyruvate dehydrogenase and DnaK) were identified under both planktonic and biofilm growth conditions. In conclusion, the protein expression pattern of SS, grown as biofilm, was different from the SS grown as planktonic cells. These five immunogenic proteins that were specific to SS biofilm cells may potentially be targeted as vaccine candidates to protect against SS biofilm infections. The four proteins common to both biofilm and planktonic cells can be targeted as vaccine candidates to protect against both biofilm and acute infections.

Role of the Streptococcus agalactiae ClpP serine protease in heat-induced stress defence and growth arrest

The main causes of microbial death after heat exposure are not well understood. Here, it is shown that the heat-shock protein ClpP plays a major role in heat-induced growth arrest in Streptococcus agalactiae. A mutant lacking the ClpP protease was more sensitive to the inhibitory effects of heat, salt and oxidative stress than the isogenic wild-type strain. During growth arrest, this mutant displayed important modifications of its total protein content, including a decreased level of essential metabolic enzymes such as the alcohol dehydrogenase. Analysis of protein carbonylation demonstrated that the ClpP protease plays a role in preventing accelerated protein oxidation. Higher levels of oxidized DnaK, a key modulator of the heat-shock regulon, were observed in the ClpP mutant and these were increased following heat shock. Accumulation of oxidized/inactivated DnaK might explain why the ClpP mutant was unable to properly synthesize DNA and proteins, and why it exhibited an aberrant cell morphology. Even though ClpP plays a minor role in the virulence of S. agalactiae in a murine infection model, the data presented here point to the importance of ClpP in oxidative stress defence in preventing heat-induced cell alterations.

Streptococcus pneumoniae heat shock protein 70 does not induce human antibody responses during infection

Mouse monoclonal antibodies (mAbs) were developed against Streptococcus pneumoniae in search for potential common pneumococcal proteins as vaccine antigens. mAb 230,B-9 (IgG1) reacted by immunoblotting with a 70-kDa protein which was isolated by immunoaffinity chromatography and subsequent preparative electrophoresis. N-terminal amino acid sequencing showed homology to that of heat shock protein 70 (hsp70). The hsp70 epitope reactive with mAb 230,B-9 was found in all the pneumococci examined as well as in other streptococci and enterococci. The epitope was not expressed in several other examined Gram-positive or -negative bacteria. Pneumococcal hsp70 has by other investigators been proposed to be a vaccine candidate. Binding experiments using flow cytometry showed that the epitope was not surface-exposed on live exponential phase grown S. pneumoniae. Human patient sera did not react with affinity-purified pneumococcal hsp70. Therefore the pneumococcal hsp70 does not seem to be of special interest in a vaccine formulation. The human sera contained antibodies to high molecular proteins co-purified with hsp70. Some of these proteins could be the pneumococcal surface protein A.

Detection of 23 immunogenic pneumococcal proteins using convalescent-phase serum

A genomic expression library of Streptococcus pneumoniae was screened with a convalescent-phase serum for immunoreactive proteins. Six known and 17 unknown pneumococcal proteins were detected. Five of the known proteins were surface-located virulence factors, and eight of the unknown proteins were putative membrane proteins.

Limited stress response in Streptococcus pneumoniae

In Streptococcus pneumoniae, heat shock induces the synthesis of 65-, 73-, and 84-kDa proteins, and ethanol shock induces a 104-kDa protein. In this study, the 65-, 84-, and 104-kDa proteins were identified as members of the GroEL, ClpL and alcohol dehydrogenase families, respectively, and the general properties of the stress response of S. pneumoniae to several other stresses were characterized. However, several stresses which are known to induce stress responses in Escherichia coli and Bacillus subtilis failed to induce any high molecular weight heat-shock proteins (HSPs) such as GroEL and DnaK homologues. A minor temperature shift from 30 to 37 C triggered induction of the homologues of DnaK and GroEL of E. coli. These features may provide a foundation for evaluating the role of heat-shock proteins relative to the physiology and pathogenesis of pneumococcus.