MO946: Factors Associated With Changes in Health-Related Quality of Life (Hrqol) in A Greek Cohort of Kidney Transplant Recipients: A Prospective Study

BACKGROUND AND AIMS

Kidney transplantation is recognized as the treatment of choice for patients with End Stage Kidney Disease (ESKD). Improvement in short term patient and graft survival of kidney transplant recipients (KTRs), has shifted interest to the long-term outcomes and Health-Related Quality of Life (HRQoL) estimation is closely related. Thus, reliable evaluation of HRQoL with disease-specific questionnaires is of great importance. The aim of our study was to assess prospectively possible changes in HRQoL during follow up period and to identify associated factors that might affect these changes.

METHOD

We used the Greek version of the translated and adapted by our team disease-specific instrument Kidney Transplant Questionnaire 25 (KTQ-25) and the Greek SF-36 were administered in a cohort of KTRs during their routine visit in the transplant outpatient clinic twice, at study entry and after one year. Sociodemographic and medical information were also collected at both time points. Inclusion criteria were, aged ≥18-year-old, time since transplant ≥1 year, functioning transplant. All participants provided written informed consent.

RESULTS

A total of 84 KTRs (59 males; mean age 53.5 ± 10.7; mean e-GFR 47.7 ± 15.1 mL/min/1.73 m2; average time since transplantation 55.7 ± 48.3 months) included in the study at the first time point, while 74 KTRs (88.1%) remained for the second assessment (3 died, 4 denied and 4 changed transplant unit). The majority of KTRs were married (73.8%), with children (77.4%), non-smokers (81.6%) and retired (60.7%). The 45.8% had family monthly income ≤ 1000€. In 62%, hemodialysis was the modality before transplantation and 59.52% had received graft from deceased donor. Immunosuppressive treatment was 84.34% corticosteroids, 54.22% Tacrolimus, 40.96% Cyclosporine, 91.75% MMF and 3.61% Azathioprine. The observed SF-36 scores in all dimensions both time-points were similar without significant changes. Also, no significant changes found between the two time-points at all 5 dimensions and total score of the KTQ-25. A multivariate regression analysis for the 5 dimensions of the KTQ-25 at the second time-point was done. Showed that variables significantly associated with Physical Symptoms dimension was age (P = 0.021) directly and Osteoporosis (P = 0.025) inversely. In regression analysis of Fatigue dimension, variables that remained significant were female sex (P = 0.046) and higher serum cholesterols’ levels (P = 0.012). Uncertainty/Fear dimension was significantly worse in KTRs with history of cardiovascular disease (P = 0.032). Appearance dimension was significantly and positively correlated with female sex and negative with age and history of cardiovascular disease (P = 0.018, P = 0.043 and P = 0.041, respectively). No significantly correlation found for Emotions dimension. Total KTQ-25 score was significantly correlated with female sex (P = 0.024), while history of cardiovascular disease had a negative impact on the score (P = 0.013).

CONCLUSION

In this one-year prospective study of the HRQoL of KTRs, no statistically significant changes were found in the scores of KTQ-25 and SF-36 instruments. Age, sex, osteoporosis, serum cholesterols’ levels and history of cardiovascular disease are some of the factors that might affect prospectively HRQoL of KTRs.

Cancer pain… who cares? International and national patterns of evidence-based global guidelines recommendations for physicians on the Web (2011 vs. 2018)

PURPOSE

Although pain is a common event during treatment of cancer, its assessment and management remains suboptimal in everyday clinical practice at global level.

METHODS

Considering both the important role of internet in daily life and that clinical guidelines are important for translating evidence in clinical practice, we performed a prospective study to scrutinize the magnitude of updated evidence-based cancer-pain guideline recommendation for physicians on the web. Changes over-time at a global level were scrutinized at two time points: 2011 for baseline and 2018 at first follow-up. Both anesthesiology and oncology societies were analyzed.

RESULTS

In 2011 we scrutinized 181,00 WebPages and 370 eligible societies were identified; 364 of these were eligible for analyses both in 2011 and 2018. The magnitude of cancer pain updated and evidence-based guideline recommendations on the web for health care providers was extremely low at global level and at any time point considered: 1.1% (4/364) in 2011 and 4.7% (17/364) in 2018. Continental and intercontinental patterns, National's highest developmental index, oncology tradition and economic-geographic areas were not found to influence cancer pain web-guideline provision. In 2018, pain & supportive care societies provided the highest rate of updated evidence-based cancer-pain guidelines for clinicians. Only 3/25 medical oncology societies and 1/34 radiation oncology societies, provided own or e-link (to other societies') evidence-based guidelines in their websites.

CONCLUSIONS

Major medical oncology and radiation oncology societies - at global level - fail to produce updated cancer pain recommendations for their physicians, with most of these providing no or inconsistent or outdated guidelines.

Postoperative chemotherapy with single-agent fluoropyrimidines after resection of colorectal cancer liver metastases: a meta-analysis of randomised trials

Surgical resection is the only option of cure for patients with metastatic colorectal cancer. Risk of recurrence after metastasectomy is around 75%. Use of adjuvant chemotherapy after metastasectomy is controversial.

Normochromic normocytic anemia in a postmenopausal woman with severe osteoporosis treated with intermittent parathyroid hormone

Intermittent exogenous parathyroid hormone (PTH) is a potent osteoanabolic agent used for the treatment of severe osteoporosis. Two molecules of recombinant PTH are commercially available: the full-length PTH (PTH 1-84) and teriparatide (PTH 1-34). We present the first report of PTH-induced mild, asymptomatic, normochromic normocytic anemia in a postmenopausal woman treated sequentially with PTH 1-84 and PTH 1-34. Anemia was more pronounced with PTH 1-84 compared to PTH 1-34 and was reversed with each regimen discontinuation. We suggest monitoring of hematocrit and hemoglobin in PTH-treated patients, especially when PTH 1-84 is used.

[Comparison of the genome for phylogenetically related bacteriophages phiKZ and EL of Pseudomonas aeruginosa: evolutionary aspects and minimal genome size]

Bacteriophages of the family Myoviridae represent one of the most widespread domains of the biosphere substantially affecting the ecological balance of microorganisms. Interestingly, sequence analysis of genomic DNAs of large bacteriophages revealed many genes coding for proteins with unknown functions. A new approach is proposed to improve the functional identification of genes. This approach is based on comparing the genome sequence for phylogenetically and morphologically related phages showing no considerable homology at the level of genomic DNA. It is assumed that gene functions essential for the development of phages of a given family are conserved and that the corresponding genes code for similar orthologous proteins even when lacking sequence homology. The genome was sequenced and compared for two Pseudomonas aeruginosa giant bacteriophages, phiKZ and EL, which belong to a group of (phiKZ-related phages. A substantial difference in genome organization was observed, suggesting specific features of phage evolution. In addition, the problem of the minimal genome of the superfamily is discussed on the basis of the difference in size and structure between the phiKZ and EL genomes.

The djlA gene acts synergistically with dnaJ in promoting Escherichia coli growth

The DnaK chaperone of Escherichia coli is known to interact with the J domains of DnaJ, CbpA, and DjlA. By constructing multiple mutants, we found that the djlA gene was essential for bacterial growth above 37 degrees C in the absence of dnaJ. This essentiality depended upon the J domain of DjlA but not upon the normal membrane location of DjlA.

Structure-function analysis of the zinc-binding region of the Clpx molecular chaperone

The ClpX heat shock protein of Escherichia coli is a member of the universally conserved Hsp100 family of proteins, and possesses a putative zinc finger motif of the C(4) type. The ClpX is an ATPase which functions both as a substrate specificity component of the ClpXP protease and as a molecular chaperone. Using an improved purification procedure we show that the ClpX protein is a metalloprotein complexed with Zn(II) cations. Contrary to other Hsp100 family members, ClpXZn(II) exists in an oligomeric form even in the absence of ATP. We show that the single ATP-binding site of ClpX is required for a variety of tasks, namely, the stabilization of the ClpXZn(II) oligomeric structure, binding to ClpP, and the ClpXP-dependent proteolysis of the lambdaO replication protein. Release of Zn(II) from ClpX protein affects the ability of ClpX to bind ATP. ClpX, free of Zn(II), cannot oligomerize, bind to ClpP, or participate in ClpXP-dependent proteolysis. We also show that ClpXDeltaCys, a mutant protein whose four cysteine residues at the putative zinc finger motif have been replaced by serine, behaves in similar fashion as wild type ClpX protein whose Zn(II) has been released either by denaturation and renaturation, or chemically by p-hydroxymercuriphenylsulfonic acid.

Identification of important amino acid residues that modulate binding of Escherichia coli GroEL to its various cochaperones

Genetic experiments have shown that the GroEL/GroES chaperone machine of Escherichia coli is absolutely essential, not only for bacterial growth but also for the propagation of many bacteriophages including lambda. The virulent bacteriophages T4 and RB49 are independent of the host GroES function, because they encode their own cochaperone proteins, Gp31 and CocO, respectively. E. coli groEL44 mutant bacteria do not form colonies above 42 degrees nor do they propagate bacteriophages lambda, T4, or RB49. We found that the vast majority (40/46) of spontaneous groEL44 temperature-resistant colonies at 43 degrees were due to the presence of an intragenic suppressor mutation. These suppressors define 21 different amino acid substitutions in GroEL, each affecting one of 13 different amino acid residues. All of these amino acid residues are located at or near the hinge, which regulates the large en bloc movements of the GroEL apical domain. All of these intragenic suppressors support bacteriophages lambda, T4, and RB49 growth to various extents in the presence of the groEL44 allele. Since it is known that the GroEL44 mutant protein does not interact effectively with Gp31, the suppressor mutations should enhance cochaperone binding. Analogous intragenic suppressor studies were conducted with the groEL673 temperature-sensitive allele.

Pseudo-T-even bacteriophage RB49 encodes CocO, a cochaperonin for GroEL, which can substitute for Escherichia coli's GroES and bacteriophage T4's Gp31

Bacteriophage T4-encoded Gp31 is a functional ortholog of the Escherichia coli GroES cochaperonin protein. Both of these proteins form transient, productive complexes with the GroEL chaperonin, required for protein folding and other related functions in the cell. However, Gp31 is specifically required, in conjunction with GroEL, for the correct folding of Gp23, the major capsid protein of T4. To better understand the interaction between GroEL and its cochaperonin cognates, we determined whether the so-called "pseudo-T-even bacteriophages" are dependent on host GroEL function and whether they also encode their own cochaperonin. Here, we report the isolation of an allele-specific mutation of bacteriophage RB49, called epsilon22, which permits growth on the E. coli groEL44 mutant but not on the isogenic wild type host. RB49 epsilon22 was used in marker rescue experiments to identify the corresponding wild type gene, which we have named cocO (cochaperonin cognate). CocO has extremely limited identity to GroES but is 34% identical and 55% similar at the protein sequence level to T4 Gp31, sharing all of the structural features of Gp31 that distinguish it from GroES. CocO can substitute for Gp31 in T4 growth and also suppresses the temperature-sensitive phenotype of the E. coli groES42 mutant. CocO's predicted mobile loop is one residue longer than that of Gp31, with the epsilon22 mutation resulting in a Q36R substitution in this extra residue. Both the CocO wild type and epsilon22 proteins have been purified and shown in vitro to assist GroEL in the refolding of denatured citrate synthase.

DjlA is a third DnaK co-chaperone of Escherichia coli, and DjlA-mediated induction of colanic acid capsule requires DjlA-DnaK interaction

DjlA is a 30-kDa type III membrane protein of Escherichia coli with the majority, including an extreme C-terminal putative J-domain, oriented toward the cytoplasm. No other regions of sequence similarity aside from the J-domain exist between DjlA and the known DnaK (Hsp70) co-chaperones DnaJ (Hsp40) and CbpA. In this study, we explored whether and to what extent DjlA possesses DnaK co-chaperone activity and under what conditions a DjlA-DnaK interaction could be important to the cell. We found that the DjlA J-domain can substitute fully for the J-domain of DnaJ using various in vivo functional complementation assays. In addition, the purified cytoplasmic fragment of DjlA was shown to be capable of stimulating DnaK ATPase in a manner indistinguishable from DnaJ, and, furthermore, DjlA could act as a DnaK co-chaperone in the reactivation of chemically denatured luciferase in vitro. DjlA expression in the cell is tightly controlled, and even its mild overexpression leads to induction of mucoid capsule. Previous analysis showed that DjlA-mediated induction of the wca capsule operon required the RcsC/RcsB two-component signaling system and that wca induction by DjlA was lost when cells contained mutations in either the dnaK or grpE gene. We now show using allele-specific genetic suppression analysis that DjlA must interact with DnaK for DjlA-mediated stimulation of capsule synthesis. Collectively, these results demonstrate that DjlA is a co-chaperone for DnaK and that this chaperone-co-chaperone pair is implicated directly, or indirectly, in the regulation of colanic acid capsule.

Genetic analysis of bacteriophage-encoded cochaperonins

Early genetic studies identified the Escherichia coli groES and groEL genes because mutations in them blocked the growth of bacteriophages lambda and T4. Subsequent genetic and biochemical analyses have shown that GroES and GroEL constitute a chaperonin machine, absolutely essential for E. coli growth, because it is needed for the correct folding of many of its proteins. In spite of very little sequence identity to GroES, the bacteriophage T4-encoded Gp31 protein and the bacteriophage RB49-encoded CocO protein are bona fide GroEL cochaperonins, even capable of substituting for GroES in E. coli growth. A major functional distinction is that only Gp31 and CocO can assist GroEL in the correct folding of Gp23, the major bacteriophage capsid protein. Conserved structural features between CocO and Gp31, which are absent from GroES, highlight their potential importance in specific cochaperonin function.

The importance of a mobile loop in regulating chaperonin/ co-chaperonin interaction: humans versus Escherichia coli

Chaperonins are universally conserved proteins that nonspecifically facilitate the folding of a wide spectrum of proteins. While bacterial GroEL is functionally promiscuous with various co-chaperonin partners, its human homologue, Hsp60 functions specifically with its co-chaperonin partner, Hsp10, and not with other co-chaperonins, such as the bacterial GroES or bacteriophage T4-encoded Gp31. Co-chaperonin interaction with chaperonin is mediated by the co-chaperonin mobile loop that folds into a beta-hairpin conformation upon binding to the chaperonin. A delicate balance of flexibility and conformational preferences of the mobile loop determines co-chaperonin affinity for chaperonin. Here, we show that the ability of Hsp10, but not GroES, to interact specifically with Hsp60 lies within the mobile loop sequence. Using mutational analysis, we show that three substitutions in the GroES mobile loop are necessary and sufficient to acquire Hsp10-like specificity. Two of these substitutions are predicted to preorganize the beta-hairpin turn and one to increase the hydrophobicity of the GroEL-binding site. Together, they result in a GroES that binds chaperonins with higher affinity. It seems likely that the single ring mitochondrial Hsp60 exhibits intrinsically lower affinity for the co-chaperonin that can be compensated for by a higher affinity mobile loop.

Genetic analysis of the bacteriophage T4-encoded cochaperonin Gp31

Previous genetic and biochemical analyses have established that the bacteriophage T4-encoded Gp31 is a cochaperonin that interacts with Escherichia coli's GroEL to ensure the timely and accurate folding of Gp23, the bacteriophage-encoded major capsid protein. The heptameric Gp31 cochaperonin, like the E. coli GroES cochaperonin, interacts with GroEL primarily through its unstructured mobile loop segment. Upon binding to GroEL, the mobile loop adopts a structured, beta-hairpin turn. In this article, we present extensive genetic data that strongly substantiate and extend these biochemical studies. These studies begin with the isolation of mutations in gene 31 based on the ability to plaque on groEL44 mutant bacteria, whose mutant product interacts weakly with Gp31. Our genetic system is unique because it also allows for the direct selection of revertants of such gene 31 mutations, based on their ability to plaque on groEL515 mutant bacteria. Interestingly, all of these revertants are pseudorevertants because the original 31 mutation is maintained. In addition, we show that the classical tsA70 mutation in gene 31 changes a conserved hydrophobic residue in the mobile loop to a hydrophilic one. Pseudorevertants of tsA70, which enable growth at the restrictive temperatures, acquire the same mutation previously shown to allow plaque formation on groEL44 mutant bacteria. Our genetic analyses highlight the crucial importance of all three highly conserved hydrophobic residues of the mobile loop of Gp31 in the productive interaction with GroEL.

Polypeptide flux through bacterial Hsp70: DnaK cooperates with trigger factor in chaperoning nascent chains

A role for DnaK, the major E. coli Hsp70, in chaperoning de novo protein folding has remained elusive. Here we show that under nonstress conditions DnaK transiently associates with a wide variety of nascent and newly synthesized polypeptides, with a preference for chains larger than 30 kDa. Deletion of the nonessential gene encoding trigger factor, a ribosome-associated chaperone, results in a doubling of the fraction of nascent polypeptides interacting with DnaK. Combined deletion of the trigger factor and DnaK genes is lethal under normal growth conditions. These findings indicate important, partially overlapping functions of DnaK and trigger factor in de novo protein folding and explain why the loss of either chaperone can be tolerated by E. coli.

Recognition, targeting, and hydrolysis of the lambda O replication protein by the ClpP/ClpX protease

It has previously been established that sequences at the C termini of polypeptide substrates are critical for efficient hydrolysis by the ClpP/ClpX ATP-dependent protease. We report for the bacteriophage lambda O replication protein, however, that N-terminal sequences play the most critical role in facilitating proteolysis by ClpP/ClpX. The N-terminal portion of lambda O is degraded at a rate comparable with that of wild type O protein, whereas the C-terminal domain of O is hydrolyzed at least 10-fold more slowly. Consistent with these results, deletion of the first 18 amino acids of lambda O blocks degradation of the N-terminal domain, whereas proteolysis of the O C-terminal domain is only slightly diminished as a result of deletion of the C-terminal 15 amino acids. We demonstrate that ClpX retains its capacity to bind to the N-terminal domain following removal of the first 18 amino acids of O. However, ClpX cannot efficiently promote the ATP-dependent binding of this truncated O polypeptide to ClpP, the catalytic subunit of the ClpP/ClpX protease. Based on our results with lambda O protein, we suggest that two distinct structural elements may be required in substrate polypeptides to enable efficient hydrolysis by the ClpP/ClpX protease: (i) a ClpX-binding site, which may be located remotely from substrate termini, and (ii) a proper N- or C-terminal sequence, whose exposure on the substrate surface may be induced by the binding of ClpX.

On the mechanism of FtsH-dependent degradation of the sigma 32 transcriptional regulator of Escherichia coli and the role of the Dnak chaperone machine

The Escherichia coli sigma 32 transcriptional regulator has been shown to be degraded both in vivo and in vitro by the FtsH (HflB) protease, a member of the AAA protein family. In our attempts to study this process in detail, we found that two sigma 32 mutants lacking 15-20 C-terminal amino acids had substantially increased half-lives in vivo or in vitro, compared with wild-type sigma 32. A truncated version of sigma 32, sigma 32 C delta, was purified to homogeneity and shown to be resistant to FtsH-dependent degradation in vitro, suggesting that FtsH initiates sigma 32 degradation from its extreme C-terminal region. Purified sigma 32 C delta interacted with the DnaK and DnaJ chaperone proteins in a fashion similar to that of wild-type sigma 32. However, in contrast to wild-type sigma 32, sigma 32 C delta was largely deficient in its in vivo and in vitro interaction with core RNA polymerase. As a consequence, the truncated sigma 32 protein was completely non-functional in vivo, even when overproduced. Furthermore, it is shown that wild-type sigma 32 is protected from degradation by FtsH when complexed to the RNA polymerase core, but sensitive to proteolysis when in complex with the DnaK chaperone machine. Our results are in agreement with the proposal that the capacity of the DnaK chaperone machine to autoregulate its own synthesis negatively is simply the result of its ability to sequester sigma 32 from RNA polymerase, thus making it accessible to degradation by the FtsH protease.

Compensatory changes in GroEL/Gp31 affinity as a mechanism for allele-specific genetic interaction

Previous work has shown that the GroEL-GroES interaction is primarily mediated by the GroES mobile loop. In bacteriophage T4 infection, GroES is substituted by the gene 31-encoded cochaperonin, Gp31. Using a genetic selection scheme, we have identified a new set of mutations in gene 31 that affect interaction with GroEL; all mutations result in changes in the mobile loop of Gp31. Biochemical analyses reveal that the mobile loop mutations alter the affinity between Gp31 and GroEL, most likely by modulating the stability of the GroEL-bound hairpin conformation of the mobile loop. Surprisingly, mutations in groEL that display allele-specific interactions with mutations in gene 31 alter residues in the GroEL intermediate domain, distantly located from the mobile loop binding site. The observed patterns of genetic and biochemical interaction between GroES or Gp31 and GroEL point to a mechanism of genetic allele specificity based on compensatory changes in affinity of the protein-protein interaction. Mutations studied in this work indirectly alter affinity by modulating a folding transition in the Gp31 mobile loop or by modulating a hinged conformational change in GroEL.

Formation of the preprimosome protects lambda O from RNA transcription-dependent proteolysis by ClpP/ClpX

Using the bacteriophage lambda DNA replication system, composed entirely of purified proteins, we have tested the accessibility of the short-lived lambda O protein to the ClpP/ClpX protease during the various stages of lambda DNA replication. We find that binding of lambda O protein to its orilambda DNA sequence, leading to the so-called "O-some" formation, largely inhibits its degradation. On the contrary, under conditions permissive for transcription, the lambda O protein bound to the orilambda sequence becomes largely accessible to ClpP/ClpX-mediated proteolysis. However, when the lambda O protein is part of the larger orilambda:O.P.DnaB preprimosomal complex, transcription does not significantly increase ClpP/ClpX-dependent lambda O degradation. These results show that transcription can stimulate proteolysis of a protein that is required for the initiation of DNA replication.

The oligomeric structure of GroEL/GroES is required for biologically significant chaperonin function in protein folding

Two models are being considered for the mechanism of chaperonin-assisted protein folding in E. coli: (i) GroEL/GroES act primarily by enclosing substrate polypeptide in a folding cage in which aggregation is prevented during folding. (ii) GroEL mediates the repetitive unfolding of misfolded polypeptides, returning them onto a productive folding track. Both models are not mutually exclusive, but studies with the polypeptide-binding domain of GroEL have suggested that unfolding is the primary mechanism, enclosure being unnecessary. Here we investigate the capacity of the isolated apical polypeptide-binding domain to functionally replace the complete GroEL/GroES system. We show that the apical domain binds aggregation-sensitive polypeptides but cannot significantly assist their refolding in vitro and fails to replace the groEL gene or to complement defects of groEL mutants in vivo. A single-ring version of GroEL cannot substitute for GroEL. These results strongly support the view that sequestration of aggregation-prone intermediates in a folding cage is an important element of the chaperonin mechanism.

Genetic and biochemical characterization of mutations affecting the carboxy-terminal domain of the Escherichia coli molecular chaperone DnaJ

DnaJ is a universally conserved heat shock protein involved in protein folding. DnaJ contains four conserved domains. The N-terminal 'J-domain' has been shown to be responsible for the recruitment of its specific DnaK partner protein. The 'Gly/Phe'- and 'Cys-rich' domains have been implicated in stabilizing interactions with DnaK. DnaJ is also able to interact independently with unfolded or native polypeptides. Very little is known regarding such binding/chaperone abilities, but it has been suggested that the least conserved carboxy-terminal domain could contribute to these properties. To gain insight into the biological activity of this fourth domain, we deleted two relatively conserved patches of amino acid residues, a 'G-rich' cluster and a 'G-D-L-Y-V' motif, resulting in the DnaJDelta[230-238] and DnaJDelta[242-246] mutant proteins respectively. Both mutant proteins are partially defective in stimulating the ATPase activity of DnaK and in preventing aggregation of firefly luciferase in vitro. Both mutants have lost the ability to regulate the sigma32-dependent heat shock response, as shown in vivo using a heat shock transcriptional fusion. Furthermore, and unlike wild-type DnaJ, DnaJDelta[242-246] is unable to assist the DnaK-dependent refolding of denatured luciferase. In agreement with these results, we found that DnaJDelta[242-246] is unable to restore either the temperature-sensitive phenotype or the motility defect of a dnaJ null mutation. Substitution of amino acids [242-246] by five alanines leads to similar phenotypic defects, suggesting that altering the 'G-D-L-Y-V' motif leads to partial loss of DnaJ activity. Our data clearly support a role in the intrinsic chaperone/substrate binding ability of the carboxy-terminal domain of DnaJ.

Function of Escherichia coli MsbA, an essential ABC family transporter, in lipid A and phospholipid biosynthesis

The Escherichia coli msbA gene, first identified as a multicopy suppressor of htrB mutations, has been proposed to transport nascent core-lipid A molecules across the inner membrane (Polissi, A., and Georgopoulos, C. (1996) Mol. Microbiol. 20, 1221-1233). msbA is an essential E. coli gene with high sequence similarity to mammalian Mdr proteins and certain types of bacterial ABC transporters. htrB is required for growth above 32 degreesC and encodes the lauroyltransferase that acts after Kdo addition during lipid A biosynthesis (Clementz, T., Bednarski, J., and Raetz, C. R. H. (1996) J. Biol. Chem. 271, 12095-12102). By using a quantitative new 32Pi labeling technique, we demonstrate that hexa-acylated species of lipid A predominate in the outer membranes of wild type E. coli labeled for several generations at 42 degreesC. In contrast, in htrB mutants shifted to 42 degreesC for 3 h, tetra-acylated lipid A species and glycerophospholipids accumulate in the inner membrane. Extra copies of the cloned msbA gene restore the ability of htrB mutants to grow at 42 degreesC, but they do not increase the extent of lipid A acylation. However, a significant fraction of the tetra-acylated lipid A species that accumulate in htrB mutants are transported to the outer membrane in the presence of extra copies of msbA. E. coli strains in which msbA synthesis is selectively shut off at 42 degreesC accumulate hexa-acylated lipid A and glycerophospholipids in their inner membranes. Our results support the view that MsbA plays a role in lipid A and possibly glycerophospholipid transport. The tetra-acylated lipid A precursors that accumulate in htrB mutants may not be transported as efficiently by MsbA as are penta- or hexa-acylated lipid A species.

The ins and outs of a molecular chaperone machine

Genetic and biochemical work has highlighted the biological importance of the GroEL/GroES (Hsp60/Hsp10; cpn60/cpn10) chaperone machine in protein folding. GroEL's donut-shaped structure has attracted the attention of structural biologists because of its elegance as well as the secrets (substrates) it can hide. The recent determination of the GroES and GroEL/GroES structures provides a glimpse of their plasticity, revealing dramatic conformational changes that point to an elaborate mechanism, coupling ATP hydrolysis to substrate release by GroEL.

Purification and biochemical properties of Saccharomyces cerevisiae Mdj1p, the mitochondrial DnaJ homologue

The DnaK/DnaJ/GrpE heat shock proteins of Escherichia coli constitute the prototype DnaK chaperone machine. Various studies have shown that these three proteins work synergistically in a diverse array of biological functions, including protein folding and disaggregation, proteolysis, and transport across biological membranes. We have overexpressed and purified the mitochondrial Saccharomyces cerevisiae DnaJ homologue, Mdj1pDelta55, which lacks the mitochondrial presequence, and studied its biochemical properties in well defined in vitro systems. We find that Mdj1pDelta55 interacts with DnaK as judged both by an enzyme-linked immunosorbent assay, as well as stimulation of DnaK's weak ATPase activity in the presence of GrpE. In addition, Mdj1pDelta55 not only interacts with denatured firefly luciferase on its own, but also enables DnaK to bind to it in an ATP-dependent mode. Using co-immunoprecipitation assays we can demonstrate the presence of a stable Mdj1pDelta55-luciferase-DnaK complex. However, in contrast to DnaJ, Mdj1pDelta55 does not appear to interact well with certain seemingly folded proteins, such as the sigma32 heat shock transcription factor or the lambdaP DNA replication protein. Finally, Mdj1pDelta55 can substitute perfectly well for DnaJ in the refolding of denatured firefly luciferase by the DnaK chaperone machine. These studies demonstrate that Mdj1pDelta55 has conserved most of DnaJ's known biological properties, thus supporting an analogous functional role in yeast mitochondria.

Structure-function analyses of the Ssc1p, Mdj1p, and Mge1p Saccharomyces cerevisiae mitochondrial proteins in Escherichia coli

The DnaK, DnaJ, and GrpE proteins of Escherichia coli have been universally conserved across the biological kingdoms and work together to constitute a highly efficient molecular chaperone machine. We have examined the extent of functional conservation of Saccharomyces cerevisiae Ssc1p, Mdj1p, and Mge1p by analyzing their ability to substitute for their corresponding E. coli homologs in vivo. We found that the expression of yeast Mge1p, the GrpE homolog, allowed for the deletion of the otherwise essential grpE gene of E. coli, albeit only up to 40 degrees C. The inability of Mge1p to substitute for GrpE at very high temperatures is consistent with our previous finding that it specifically failed to stimulate DnaK's ATPase at such extreme conditions. In contrast to Mge1p, overexpression of Mdj1p, the DnaJ homolog, was lethal in E. coli. This toxicity was specifically relieved by mutations which affected the putative zinc binding region of Mdj1p. Overexpression of a truncated version of Mdj1p, containing the J- and Gly/Phe-rich domains, partially substituted for DnaJ function at high temperature. A chimeric protein, consisting of the J domain of Mdj1p coupled to the rest of DnaJ, acted as a super-DnaJ protein, functioning even more efficiently than wild-type DnaJ. In contrast to the results with Mge1p and Mdj1p, both the expression and function of Ssc1p, the DnaK homolog, were severely compromised in E. coli. We were unable to demonstrate any functional complementation by Ssc1p, even when coexpressed with its Mdj1p cochaperone in E. coli.

Positive control of the two-component RcsC/B signal transduction network by DjlA: a member of the DnaJ family of molecular chaperones in Escherichia coli

The membrane-anchored DjIA protein represents the third member of the DnaJ 'J-domain' family of Escherichia coli that includes DnaJ and CbpA. DjIA possesses a J-domain at its extreme C-terminus but shares no additional homology with DnaJ. Our genetic analysis suggests that DjIA acts in concert with the RcsB/C two-component signal transduction system to augment induction of the cps (capsular polysaccharide) operon and synthesis of colanic acid mucoid capsule. The DjIA J-domain is essential for the observed stimulation of this pathway as deletion, or introduction of the mutation H233Q, within the highly conserved HPD tripeptide abolished all inducing activity. Deletion of the transmembrane anchor sequence also abolished all inducing activity. djIA is not an essential gene under all conditions tested, nor is it essential for mucoid capsule biosynthesis; however, strong overexpression leads to rapid loss of cell viability suggesting that the gene is normally tightly regulated. Northern analysis revealed that djIA message was extremely unstable but could be induced or stabilized in response to cold shock. The activation of the cps operon by DjIA is dependent upon both DnaK(Hsp70) and GrpE, and therefore we propose a role for DjIA, together with this chaperone machine, as a novel regulator of a two-component histidine kinase signal transduction pathway.

The T/t common exon of simian virus 40, JC, and BK polyomavirus T antigens can functionally replace the J-domain of the Escherichia coli DnaJ molecular chaperone

The N-terminal 70 residue "J-domain" of the Escherichia coli DnaJ molecular chaperone is the defining and highly conserved feature of a large protein family. Based upon limited, yet significant, amino acid sequence homology to the J-domain, the DNA encoding the T/t common exon of the simian virus 40 (SV40), JC, or BK polyoma virus T antigen oncoproteins was used to construct J-domain replacement chimeras of the E. coli DnaJ chaperone. The virally encoded J-domains successfully substituted for the bacterial counterpart in vivo as shown by (i) complementation for viability at low and high temperature of a hypersensitive bacterial reporter strain, and (ii) the restoration of bacteriophage lambda plaque forming ability in the same strain. The amino acid change, H42Q, in the SV40 T/t and the JC virus T/t exon, which is positionally equivalent to the canonical dnaJ259 H33Q mutation within the E. coli J-domain, entirely abolished complementing activity. These results strongly suggest that the heretofore functionally undefined viral T/t common exon represents a bona fide J-domain that preserves critical features of the characteristic domain fold essential for J-domain interaction with the ATPase domain of the Hsp70 family. This finding has implications for the regulation of DNA tumor virus T antigens by molecular chaperones.

Modulation of the Escherichia coli sigmaE (RpoE) heat-shock transcription-factor activity by the RseA, RseB and RseC proteins

The sigma(E) (RpoE) transcription factor of Escherichia coli regulates the expression of genes whose products are devoted to extracytoplasmic activities. The sigma(E) regulon is induced upon misfolding of proteins in the periplasm or the outer membrane. Similar to other alternative sigma factors, the activity of sigma(E) is tightly regulated in E. coli. We have previously shown that sigma(E) is positively autoregulated at the transcriptional level. DNA sequencing, coupled with transcriptional analyses, have shown that sigma(E) is encoded by the first gene of a four-gene operon. The second gene of this operon, rseA, encodes an anti-sigma(E) activity. This was demonstrated at both the genetic and biochemical levels. For example, mutations in rseA constitutively increase sigma(E) activity. Consistent with this, overproduction of RseA leads to an inhibitory effect on sigma(E) activity. Topological analysis of RseA suggests the existence of one transmembrane domain, with the N-terminal part localized in the cytoplasm. Overproduction of this N-terminal domain alone was shown to inhibit sigma(E) activity. These observations were confirmed in vitro, because either purified RseA or only its purified N-terminal domain inhibited transcription from Esigma(E)-dependent promoters. Furthermore, RseA and sigma(E) co-purify, and can be co-immunoprecipitated, and chemically cross-linked. The sigma(E) activity is further modulated by the products of the remaining genes in this operon, rseB and rseC. RseB is a periplasmic protein, which negatively regulates sigma(E) activity and specifically interacts with the C-terminal periplasmic domain of RseA. In contrast, RseC is an inner membrane protein that positively modulates sigma(E) activity. Most of these protein-protein interactions were verified in vivo using the yeast two-hybrid system.

Identification and characterization of HsIV HsIU (ClpQ ClpY) proteins involved in overall proteolysis of misfolded proteins in Escherichia coli

Heat shock response in Escherichia coli is autoregulated. Consistent with this, mutations in certain heat shock genes, such as dnaK, dnaJ, grpE or htrC lead to a higher constitutive heat shock gene expression at low temperatures. A similar situation occurs upon accumulation of newly synthesized peptides released prematurely from the ribosomes by puromycin. We looked for gene(s) which, when present in multicopy, prevent the constitutive heat shock response associated with htrC mutant bacteria or caused by the presence of puromycin. One such locus was identified and shown to carry the recently sequenced hslV hslU (clpQ clpY) operon. HslV/ClpQ shares a very high degree of homology with members of the beta-type subunit, constituting the catalytic core of the 20S proteasome. HslU/ClpY is 50% identical to the ClpX protein of E. coli, which is known to present large polypeptides to its partner, the ATP-independent proteolytic enzyme ClpP. We show that, in vivo, HslV and HslU interact and participate in the degradation of abnormal puromycylpolypeptides. Biochemical evidence suggests that HslV/ClpQ is an efficient peptidase whose activity is enhanced by HslU/CIpY in the presence of ATP.

Interplay of structure and disorder in cochaperonin mobile loops

Protein-protein interactions typically are characterized by highly specific interfaces that mediate binding with precisely tuned affinities. Binding of the Escherichia coli cochaperonin GroES to chaperonin GroEL is mediated, at least in part, by a mobile polypeptide loop in GroES that becomes immobilized in the GroEL/GroES/nucleotide complex. The bacteriophage T4 cochaperonin Gp31 possesses a similar highly flexible polypeptide loop in a region of the protein that shows low, but significant, amino acid similarity with GroES and other cochaperonins. When bound to GroEL, a synthetic peptide representing the mobile loop of either GroES or Gp31 adopts a characteristic bulged hairpin conformation as determined by transferred nuclear Overhauser effects in NMR spectra. Thermodynamic considerations suggest that flexible disorder in the cochaperonin mobile loops moderates their affinity for GroEL to facilitate cycles of chaperonin-mediated protein folding.

Purification and biochemical properties of Saccharomyces cerevisiae's Mge1p, the mitochondrial cochaperone of Ssc1p

Previous biochemical and genetic studies have demonstrated the universal conservation of the DnaK (Hsp70) chaperone machine. Its three members, DnaK, DnaJ, and GrpE, in Escherichia coli work synergistically to promote protein protection, disaggregation, and import into the various organelles. In the mitochondria of Saccharomyces cerevisiae the three corresponding members are designated as Ssc1p, Mdj1p, and Mge1p, respectively. The MGE1 gene was previously cloned by us and others, and its product has been shown to be absolutely essential for protein transport into mitochondria and hence cell viability. To better understand its biological role, we have proceeded to overexpress and purify the mature Mge1p in E. coli through the construction of the appropriate vector clone. Mge1p has been shown to functionally substitute for its E. coli GrpE counterpart in a variety of its biological functions, including suppression of the bacterial temperature-sensitive phenotype of the grpE280 mutation, formation of a stable complex with DnaK, stimulation of DnaK's ATPase activity, and the refolding of denatured luciferase by the DnaK/DnaJ chaperone proteins. Thus, the function of the GrpE homologues appears to be highly conserved across the biological kingdoms.

Structure-function analysis of the Escherichia coli GrpE heat shock protein

We have isolated various missense mutations in the essential grpE gene of Escherichia coli based on the inability to propagate bacteriophage lambda. To better understand the biochemical mechanisms of GrpE action in various biological processes, six mutant proteins were overexpressed and purified. All of them, GrpE103, GrpE66, GrpE2/280, GrpE17, GrpE13a and GrpE25, have single amino acid substitutions located in highly conserved regions throughout the GrpE sequence. The biochemical defects of each mutant GrpE protein were identified by examining their abilities to: (i) support in vitro lambda DNA replication; (ii) stimulate the weak ATPase activity of DnaK; (iii) dimerize and oligomerize, as judged by glutaraldehyde crosslinking and HPLC size chromatography; (iv) interact with wild-type DnaK protein using either an ELISA assay, glutaraldehyde crosslinking or HPLC size chromatography. Our results suggest that GrpE can exist in a dimeric or oligomeric form, depending on its relative concentration, and that it dimerizes/oligomerizes through its N-terminal region, most likely through a computer predicted coiled-coil region. Analysis of several mutant GrpE proteins indicates that an oligomer of GrpE is the most active form that interacts stably with DnaK and that the interaction is vital for GrpE biological function. Our results also demonstrate that both the N-terminal and C-terminal regions are important for GrpE function in lambda DNA replication and its co-chaperone activity with DnaK.

NMR structure of the J-domain and the Gly/Phe-rich region of the Escherichia coli DnaJ chaperone

The recombinant N-terminal 107-amino acid polypeptide fragment 2-108 of the DnaJ molecular chaperone of Escherichia coli, which contains the J-domain (residues 2 to 76) and the Gly/Phe-rich region (residues 77 to 108), was uniformly labeled with nitrogen-15 and carbon-13. The complete NMR solution structure of the J-domain was determined with the program DIANA on the basis of 682 nuclear Overhauser enhancement (NOE) upper distance limits and 180 dihedral angle constraints. It contains three well-defined helices comprising residues 6 to 10, 18 to 32 and 41 to 57, and a fourth helix, consisting of residues 61 to 68, which is well defined as a regular secondary structure but for which the location relative to the remainder of the molecule is not precisely determined. The helices II and III form an antiparallel helical coiled-coil. Helix I is approximately parallel to the plane defined by the helices II and III and runs from the carboxy-terminal end of the helix III to the center of helix II. Helix IV is positioned near the carboxy-terminal end of helix III and is on the same side of the coiled coil as helix I, but it is oriented approximately perpendicular to the plane of the helices II and III. This novel alpha-protein topology leads to formation of a hydrophobic core involving side-chains of all four helices. A strong correlation is seen between the extent of sequence-conservation of hydrophobic residues in the family of J-domain homologues, and the structural organization of the hydrophobic core in these proteins. The residues which have key roles for the specificity of the interaction of DnaJ-like proteins with their corresponding Hsp70 counterparts are located on the outer surfaces of the helices II and III, and in the loop connecting these two helices. Measurements of backbone amide proton exchange rates, 15N spin relaxation times and heteronuclear 15N {1H} NOEs provided additional insights into local conformational equilibria and internal rate processes in DnaJ(2-108). In the Gly/Phe-rich region, which is poorly ordered in the NMR solution structure and does not form a globular core, the polypeptide segment 90 to 103 differs from the segments 77 to 89 and 104 to 108 by reduced local flexibility. Considering that this same segment shows sequence conservation with corresponding segments in the Gly/Phe-rich regions of other DnaJ-like proteins, its reduced flexibility may be directly linked to the formation of the ternary DnaJ-DnaK-polypeptide complex.

Structure-function analysis of the zinc finger region of the DnaJ molecular chaperone

DnaJ is a molecular chaperone, which not only binds to its various protein substrates, but can also activate the DnaK cochaperone to bind to its various protein substrates as well. DnaJ is a modular protein, which contains a putative zinc finger motif of unknown function. Quantitation of the released Zn(II) ions, upon challenge with p-hydroxymercuriphenylsulfonic acid, and by atomic absorption showed that two Zn(II) ions interact with each monomer of DnaJ. Following the release of Zn(II) ions, the free cysteine residues probably form disulfide bridge(s), which contribute to overcoming the destabilizing effect of losing Zn(II). Supporting this view, infrared and circular dichroism studies show that the DnaJ secondary structure is largely unaffected by the release of Zn(II). Moreover, infrared spectra recorded at different temperatures, as well as scanning calorimetry, show that the Zn(II) ions help to stabilize DnaJ's tertiary structure. An internal 57-amino acid deletion of the cysteine-reach region did not noticeably affect the affinity of this mutant protein, DnaJDelta144-200, to bind DnaK nor its ability to stimulate DnaK's ATPase activity. However, the DnaJDelta144-200 was unable to induce DnaK to a conformation required for the stabilization of the DnaK-substrate complex. Additionally, the DnaJDelta144-200 mutant protein alone was unimpaired in its ability to interact with its final sigma32 transcription factor substrate, but exhibited reduced affinity toward its P1 RepA and lambdaP substrates. Finally, these in vitro results correlate well with the in vivo observed partial inhibition of bacteriophage lambda growth in a DnaJDelta144-200 mutant background.

Mutational analysis and properties of the msbA gene of Escherichia coli, coding for an essential ABC family transporter

The htrB gene was discovered because its insertional inactivation interfered with Escherichia coli growth and viability at temperatures above 32.5 degrees C, as a result of accumulation of phospholipids. The msbA gene was originally discovered because when cloned on a low-copy-number plasmid vector it was able to suppress the temperature-sensitive growth phenotype of an htrB null mutant as well as the accumulation of phospholipids. The msbA gene product belongs to the superfamily of ABC transporters, a universally conserved family of proteins characterized by a highly conserved ATP-binding domain. The msbA gene is essential for bacterial viability at all temperatures. In order to understand the physiological role of the MsbA protein, we mutated the ATP-binding domain using random PCR mutagenesis. Six independent mutants were isolated and characterized. Four of these mutations resulted in single-amino-acid substitutions in non-conserved residues and were able to support cell growth at 30 degrees C but not at 43 degrees C. The remaining two mutations behaved as recessive lethals, and resulted in single-amino-acid substitutions in Walker motif B, one of the two highly conserved regions of the ATP-binding domain. Despite the fact that neither of these two mutant proteins can support E. coli growth, they both retained the ability to bind ATP in vitro. In addition, we present evidence to show that N-acetyl [3H]-glucosamine, a precursor of lipopolysaccharides, accumulates at the non-permissive temperature in the inner membrane of either htrB null or msbA conditional lethal strains. Translocation of the precursor to the outer membrane is restored by transformation with a plasmid containing the wild-type msbA gene. A possible role for MsbA as a translocator of lipopolysaccharides or its precursors is discussed.

In vivo protein folding: suppressor analysis of mutations in the groES cochaperone gene of Escherichia coli

Our previous work has shown that the Escherichia coli groES14 and groES15 mutations result in reduced GroE chaperone machine function. By selecting for restoration of the ability of those mutant groES alleles to suppress the thermosensitivity of bacteria bearing the dnaA46 mutation, we isolated a number of intra- and extragenic suppressors that increase in vivo GroE chaperone function. One of the intragenic suppressors has been mapped to a segment that codes for the GroES mobile loop, previously shown to be indispensable for proper GroES/GroEL interaction. Two extragenic suppressors have been mapped to a groEL segment, previously identified by mutational analysis as coding for an important functional region of the GroEL protein. Our results should contribute to our eventual understanding of the structure-function relationships of the universally conserved GroE chaperone machine.

Both ambient temperature and the DnaK chaperone machine modulate the heat shock response in Escherichia coli by regulating the switch between sigma 70 and sigma 32 factors assembled with RNA polymerase

In Escherichia coli individual sigma factors direct RNA polymerase (RNAP) to specific promoters. Upon heat shock induction there is a transient increase in the rate of transcription of approximately 20 heat shock genes, whose promoters are recognized by the RNAP-sigma 32 rather than the RNAP-sigma 70 holoenzyme. At least three heat shock proteins, DnaK, DnaJ and GrpE, are involved in negative modulation of the sigma 32-dependent heat shock response. Here we show, using purified enzymes, that upon heat treatment of RNAP holoenzyme the sigma 70 factor is preferentially inactivated, whereas the resulting heat-treated RNAP core is still able to initiate transcription once supplemented with sigma 32 (or fresh sigma 70). Heat-aggregated sigma 70 becomes a target for the joint action of DnaK, DnaJ and GrpE proteins, which reactivate it in an ATP-dependent reaction. The RNAP-sigma 32 holoenzyme is relatively stable at temperatures at which the RNAP-sigma 70 holoenzyme is inactivated. Furthermore, we show that formation of the RNAP-sigma 32 holoenzyme is favored over that of RNAP-sigma 70 at elevated temperatures. We propose a model of negative autoregulation of the heat shock response in which cooperative action of DnaK, DnaJ and GrpE heat shock proteins switches transcription back to constitutively expressed genes through the simultaneous reactivation of heat-aggregated sigma 70, as well as sequestration of sigma 32 away from RNAP.

ATP hydrolysis is required for the DnaJ-dependent activation of DnaK chaperone for binding to both native and denatured protein substrates

Using two independent experimental approaches to monitor protein-protein interactions (enzyme-linked immunosorbent assay and size exclusion high performance liquid chromatography) we describe a general mechanism by which DnaJ modulates the binding of the DnaK chaperone to various native protein substrates, e.g. lambda P, lambda O, delta 32, P1, RepA, as well as permanently denatured alpha-carboxymethylated lactalbumin. The presence of DnaJ promotes the DnaK for efficient DnaK-substrate complex formation. ATP hydrolysis is absolutely required for such DnaJ-dependent activation of DnaK for binding to both native and denatured protein substrates. Although ADP can stabilize such as an activated DnaK-protein complex, it cannot substitute for ATP in the activation reaction. In the presence of DnaJ and ATP, DnaK possesses the affinity to different substrates which correlates well with the affinity of DnaJ alone for these protein substrates. Only when the affinity of the DnaJ chaperone for its protein substrate is relatively high (e.g. delta 32, RepA) can a tertiary complex DnaK-substrate-DnaJ be detected. In the case that DnaJ binds weakly to its substrate (lambda P, alpha-carboxymethylated lactalbumin), DnaJ is only transiently associated with the DnaK-substrate complex, but the DnaK activation reaction still occurs, albeit less efficiently.

The Escherichia coli heat shock response and bacteriophage lambda development

The Escherichia coli/bacteriophage lambda genetic interaction system has been used to uncover the existence of various biological machines. The starting point of all these studies was the isolation and characterization of E. coli mutants that blocked lambda growth, and the corresponding lambda compensatory mutations. In this manner, the lambda N-promoted transcriptional anti-termination machine was discovered composed of the NusA/NusB/NusE/NusG host proteins. In addition, the DnaK and GroEL chaperone machines were discovered composed of DnaK/DnaJ/GrpE and GroES/GroEL heat shock proteins. The individual members of the DnaK and GroEL chaperone machines have been conserved throughout evolution in both function and structure. Their biological roles include a direct involvement in lambda DNA replication and morphogenesis, the protection of proteins from aggregation, the disaggregation of various protein aggregates, the manipulation of protein structure and function, as well as the autoregulation of the heat shock response. The evolution of lambda to extensively rely on the status of the heat shock response of E. coli is likely linked to its lytic versus lysogenic choice of lifestyle. The bacteriophage T4 gp31 protein has been purified and shown to substitute for many of GroES' co-chaperonin activities.

The DnaJ chaperone catalytically activates the DnaK chaperone to preferentially bind the sigma 32 heat shock transcriptional regulator

In Escherichia coli the heat shock response is under the positive control of the sigma 32 transcription factor. Three of the heat shock proteins, DnaK, DnaI, and GrpE, play a central role in the negative autoregulation of this response at the transcriptional level. Recently, we have shown that the DnaK and DnaJ proteins can compete with RNA polymerase for binding to the sigma 32 transcription factor in the presence of ATP, by forming a stable DnaJ-sigma 32-DnaK protein complex. Here, we report that DnaJ protein can catalytically activate DnaK's ATPase activity. In addition, DnaJ can activate DnaK to bind to sigma 32 in an ATP-dependent reaction, forming a stable sigma 32-DnaK complex. Results obtained with two DnaJ mutants, a missense and a truncated version, suggest that the N-terminal portion of DnaJ, which is conserved in all family members, is essential for this activation reaction. The activated form of DnaK binds preferentially to sigma 32 versus the bacteriophage lambda P protein substrate.

The ClpX heat-shock protein of Escherichia coli, the ATP-dependent substrate specificity component of the ClpP-ClpX protease, is a novel molecular chaperone

All major classes of protein chaperones, including DnaK (the Hsp70 eukaryotic equivalent) and GroEL (the Hsp60 eukaryotic equivalent) have been found in Escherichia coli. Molecular chaperones enhance the yields of correctly folded polypeptides by preventing aggregation and even by disaggregating certain protein aggregates. Previously, we identified the ClpX heat-shock protein of E. coli because it enables the ClpP catalytic protease to degrade the bacteriophage lambda O replication protein. Here we report that ClpX alone possesses all the properties expected of a molecular chaperone protein. Specifically, it can protect the lambda O protein from heat-induced aggregation, disaggregate preformed lambda O aggregates, and even promote efficient binding of lambda O to its DNA recognition sequence. A lambda O-ClpX specific protein-protein interaction can be detected either by a modified ELISA assay or through the stimulation of ClpX's weak ATPase activity by lambda O. Unlike the behaviour of the major DnaK and GroEL chaperones, ClpX requires the presence of ATP or its non-hydrolysable analogue ATP-gamma-S for efficient interaction with other proteins including the protection of lambda O from aggregation. However, ClpX's ability to disaggregate lambda O aggregates requires hydrolysable ATP. We propose that the ClpX protein is a bona fide chaperone, whose biological role includes the maintenance of certain polypeptides in a form competent for proteolysis by the ClpP protease. Furthermore, our results suggest that the ClpX protein also performs typical chaperone protein functions independent of ClpP.

The rpoE gene encoding the sigma E (sigma 24) heat shock sigma factor of Escherichia coli

Previous work has established that the transcription factor sigma E (sigma 24) is necessary for maintaining the induction of the heat shock response of Escherichia coli at high temperatures. We have identified the gene encoding sigma E using a genetic screen designed to isolate trans-acting mutations that abolish expression from either htrA or rpoHP3, two promoters recognized uniquely by sigma E-containing RNA polymerase. Such a screen was achieved by transducing strains carrying a single copy of either phtrA-lacZ or rpoHP3-lacZ fusions with mutagenized bacteriophage P1 lysates and screening for Lac- mutant colonies at 22 degrees C. Lac- mutants were subsequently tested for inability to grow at 43 degrees C (Ts- phenotype). Only those Lac- Ts- mutants that were unable to accumulate heat shock proteins at 50 degrees C were retained for further characterization. In a complementary approach, those genes which when cloned on a multicopy plasmid led to higher constitutive expression of the sigma E regulon were characterized and mapped. Both approaches identified the same gene, rpoE, mapping at 55.5 min on the E.coli genetic map and encoding a polypeptide of 191 amino acid residues. The wild-type and a mutant rpoE gene products were over-expressed and purified. It was found that the purified wild-type sigma E protein, when used in in vitro run-off transcription assays in combination with core RNA polymerase, was able to direct transcription from the htrA and rpoHP3 promoters, but not from known sigma 70-dependent promoters. In vivo and in vitro analyses of rpoE transcriptional regulation showed that the rpoE gene is transcribed from two major promoters, one of which is positively regulated by sigma E itself.

The conserved G/F motif of the DnaJ chaperone is necessary for the activation of the substrate binding properties of the DnaK chaperone

The universally conserved DnaK and DnaJ molecular chaperone proteins bind in a coordinate manner to protein substrates to prevent aggregation, to disaggregate proteins, or to regulate proper protein function. To further examine their synergistic mechanism of action, we constructed and characterized two DnaJ deletion proteins. One has an 11-amino-acid internal deletion that spans amino acid residues 77-87 (DnaJ delta 77-87) and the other amino acids 77-107 (DnaJ delta 77-107). The DnaJ delta 77-87 mutant protein, was normal in all respects analyzed. The DnaJ delta 77-107 mutant protein has its entire G/F (Gly/Phe) motif deleted. This motif is found in most, but not all DnaJ family members. In vivo, DnaJ delta 77-107 supported bacteriophage lambda growth, albeit at reduced levels, demonstrating that at least some protein function was retained. However, DnaJ delta 77-107 did not exhibit other wild type properties, such as proper down-regulation of the heat-shock response, and had an overall poisoning effect of cell growth. The purified DnaJ delta 77-107 protein was shown to physically interact and stimulate DnaK's ATPase activity at wild type levels, unlike the previously characterized DnaJ259 point mutant (DnaJH33Q). Moreover, both DnaJ delta 77-107 and DnaJ259 bound to substrate proteins, such as sigma 32, at similar affinities as DnaJ+. However, DnaJ delta 77-107 was found to be largely defective in activating the ATP-dependent substrate binding mode of DnaK. In vivo, the ability of the mutant DnaJ proteins to down-regulate the heat-shock response was correlated only with their in vitro ability to activate DnaK to bind sigma 32, in an ATP-dependent manner, and not with their ability to bind sigma 32. We conclude, that although the G/F motif of DnaJ does not directly participate in the stimulation of DnaK's ATPase activity, nevertheless, it is involved in an important manner in modulating DnaK's substrate binding activity.

NMR structure determination of the Escherichia coli DnaJ molecular chaperone: secondary structure and backbone fold of the N-terminal region (residues 2-108) containing the highly conserved J domain

DnaJ from Escherichia coli is a 376-amino acid protein that functions in conjunction with DnaK and GrpE as a chaperone machine. The N-terminal fragment of residues 2-108, DnaJ-(2-108), retains many of the activities of the full-length protein and contains a structural motif, the J domain of residues 2-72, which is highly conserved in a superfamily of proteins. In this paper, NMR spectroscopy was used to determine the secondary structure and the three-dimensional polypeptide backbone fold of DnaJ-(2-108). By using 13C/15N doubly labeled DnaJ-(2-108), nearly complete sequence-specific assignments were obtained for 1H, 15N, 13C alpha, and 13C beta, and about 40% of the peripheral aliphatic carbon resonances were also assigned. Four alpha-helices in polypeptide segments of residues 6-11, 18-31, 41-55, and 61-68 in the J domain were identified by sequential and medium-range nuclear Overhauser effects. For the J domain, the three-dimensional structure was calculated with the program DIANA from an input of 536 nuclear Overhauser effect upper-distance constraints and 52 spin-spin coupling constants. The polypeptide backbone fold is characterized by the formation of an antiparallel bundle of two long helices, residues 18-31 and 41-55, which is stabilized by a hydrophobic core of side chains that are highly conserved in homologous J domain sequences. The Gly/Phe-rich region from residues 77 to 108 is flexibly disordered in solution.

Two classes of extragenic suppressor mutations identify functionally distinct regions of the GroEL chaperone of Escherichia coli

The GroES and GroEL proteins of Escherichia coli function together as the GroE molecular chaperone machine to (i) prevent denaturation and aggregation and (ii) assist the folding and oligomerization of other proteins without being part of the final structure. Previous genetic and biochemical analyses have determined that this activity requires interactions of the GroES 7-mer with the GroEL 14-mer. Recently, we have identified a region of the GroES protein that interacts with the GroEL protein. To identify those residues of the GroEL protein that interact with GroES, we have exploited the thermosensitive phenotype of strains bearing mutations at one or the other of two GroEL-interacting residues of GroES. We have isolated, cloned, and sequenced six suppressor mutations in groEL, three independent isolates for each groES mutant. Changes of only three different amino acid substitutions in GroEL protein were found among these six groEL suppressor mutations. On the basis of a number of in vivo analyses of the chaperone activity of various combinations of groES mutant alleles and groEL suppressor alleles, we propose that an amino-proximal region of the GroEL protein which includes amino acid residues 174 and 190 interacts with GroES and that a carboxyl-proximal region which includes residue 375 interacts with substrate proteins.

Heat shock proteins as carrier molecules: in vivo helper effect mediated by Escherichia coli GroEL and DnaK proteins requires cross-linking with antigen

In the past few years we have shown that mycobacterial heat shock proteins (hsp) of 65 and 70 kD exert a very strong helper effect in mice and monkeys when conjugated to peptides and oligosaccharides and given in the absence of adjuvants. In the present study we show that this adjuvant-free helper effect (i) is not due to lipopolysaccharide (LPS), since it was observed in LPS-resistant mice (C3H/HeJ) immunized with hsp-based constructs containing the malaria peptide (NANP)40, and (ii) is characteristic of hsp, since it was not observed with conjugates containing the mycobacterial p38 antigen, which is not a stress protein. Interestingly, the hsp GroEL and DnaK of Escherichia coli, which share a high degree of homology with the mycobacterial 65-kD and 70-kD hsp, respectively, exhibit a strong in vivo helper effect when conjugated to the (NANP)40 peptide, and the conjugates given in the absence of adjuvants. This in vivo helper behaviour of the GroEL and DnaK proteins corresponds well to that observed with the mycobacterial 65-kD and 70-kD hsp, respectively, since the hsp65- and GroEL-based constructs require previous priming of the animals with live bacille Calmette-Guérin (BCG), which is not needed for the hsp70- and DnaK-based constructs. Finally, using both mycobacterial and E. coli hsp we show that their in vivo helper effect in the absence of adjuvants requires cross-linking to the synthetic peptide. Taken together, our results suggest that the adjuvant-free helper effect observed with mycobacterial and E. coli hsp may be a generalized phenomenon, exhibited by hsp from diverse microorganisms. These findings may find applications in the design of vaccine constructs.

Isolation and characterization of point mutations in the Escherichia coli grpE heat shock gene

The Escherichia coli grpE gene (along with dnaK, dnaJ, groEL, and groES) was originally identified as one of the host factors required for phage lambda growth. The classical grpE280 mutation was the only grpE mutation that resulted from the initial screen and shown to specifically block the initiation of lambda DNA replication. Here we report the isolation of several new grpE missense mutations, again using phage lambda resistance as a selection. All mutants fall into two groups based on their temperature-dependent phenotype for lambda growth. Members of the first group (I), including grpE17 and grpE280, which was obtained again, are resistant to lambda growth at both 30 and 42 degrees C. Members of the second group (II), including grpE25, grpE66, grpE103, grpE13a, grpE57b, and grpE61, are sensitive to lambda growth at 30 degrees C but resistant at 42 degrees C. All mutations are recessive, since an E. coli grpE null mutant strain carrying these mutant alleles on low-copy-number plasmids are sensitive to infection by the lambda grpE+ transducing phage. Both group I and group II mutants are temperature sensitive for E. coli growth above 42 degrees C. The nucleotide changes were identified by sequencing analyses and shown to be dispersed throughout the latter 75% of the grpE coding region. Most of the amino acid changes occur at conserved residues, as judged by sequence comparisons between E. coli and other bacterial and yeast GrpE homologs. The isolation of these new mutations is the first step toward a structure-function analysis of the GrpE protein.

A mitochondrial homolog of bacterial GrpE interacts with mitochondrial hsp70 and is essential for viability

Mitochondrial hsp70 (mhsp70) is located in the matrix and an essential component of the mitochondrial protein import system. To study the function of mhsp70 and to identify possible partner proteins we constructed a yeast strain in which all mhsp70 molecules carry a C-terminal hexa-histidine tag. The tagged mhsp70 appears to be functional in vivo. When an ATP depleted mitochondrial extract was incubated with a nickel-derivatized affinity resin, the resin bound not only mhsp70, but also a 23 kDa protein. This protein was dissociated from mhsp70 by ATP. ADP and GTP were much less effective in promoting dissociation whereas CTP and TTP were inactive. We cloned the gene encoding the 23 kDa protein. This gene, termed GRPE, encodes a 228 residue protein, whose sequence closely resembles that of the bacterial GrpE protein. Microsequencing the purified 23 kDa protein established it as the product of the yeast GRPE gene. Yeast GrpEp is made as a precursor that is cleaved upon import into isolated mitochondria. GrpEp is essential for viability. We suggest that this protein interacts with mhsp70 in a manner analogous to that of GrpE with DnaK of E.coli.