Crystallization of the cpn6O/cpn10 complex (‘holo-chaperonin’) fromThermus thermophilus

Heat-stable enzymes from extremely thermophilic and hyperthermophilic microorganisms

Only in the last decade have microorganisms been discovered which grow near or above 100°C. The enzymes that are formed by these extremely thermophilic (growth temperature 65 to 85°C) and hyperthermophilic (growth temperature 85 to 110°C) microorganisms are of great interest. This review covers the extracellular and intracellular enzymes of these exotic microorganisms that have recently been described. Polymer-hydrolysing enzymes, such as amylolytic, cellulolytic, hemicellulolytic and proteolytic enzymes, will be discussed. In addition, the properties of the intracellular enzymes involved in carbohydrate and amino-acid metabolism and DNA-binding and chaperones and chaperone-like proteins from hyperthermophiles are described. Due to the unusual properties of these heat-stable enzymes, they are expected to fill the gap between biological and chemical processes.

Purification and characterization of chaperonin 60 and chaperonin 10 from the anaerobic thermophile Thermoanaerobacter brockii

Chaperonin 60 and chaperonin 10 (GroEL and GroES homologues, respectively) have been isolated from extracts of the anaerobic thermophile Thermoanaerobacter brockii. A simple and rapid purification for chaperonin 60 made use of hydrophobic and anion-exchange chromatographies, and could be readily scaled up; approximately 2 mg pure chaperonin 60 was obtained/g cells. In contrast with all other prokaryotic chaperonin 60 proteins that have been studied, which are tetradecamers, including those from Thermus sp., the T. brockii protein is a heptamer, and as isolated was not in association with chaperonin 10. The preparation is readily crystallized using 2-propanol or poly(ethylene glycol) with MgCl2. The N-terminal amino acid sequence of this preparation is similar to other thermophilic chaperonin 60 proteins. Chaperonin 10 was purified from the flow-through of the first hydrophobic column (which bound chaperonin 60) using a more hydrophobic adsorbent to remove contaminating proteins, followed by anion-exchange chromatography. Chaperonin 10 was obtained with a yield of approximately 10% that of chaperonin 60. The subunit molecular mass of chaperonin 10 determined by electrospray mass spectrometry is 10254 +/- 0.4 Da, which is very similar to the molecular mass of Escherichia coli GroES. Similarly, the subunit size of chaperonin 60 determined by mass spectrometry is very similar to that of GroEL, at 57949 +/- 10 Da. T. brockii chaperonin 60 has an ATPase activity that is suppressed by chaperonin 10, and the two proteins together are active in protein-folding assays. Mitochondrial malate dehydrogenase was successfully refolded at 37 degrees C after denaturation in guanidine hydrochloride, using T. brockii chaperonin 60 and chaperonin 10, or chaperonin 60 and E. coli GroES. The denatured enzyme was protected from aggregation by association with chaperonin 60. Guanidine-hydrochloride-denatured preparations of isocitrate dehydrogenase and secondary alcohol dehydrogenase isolated from T. brockii were also refolded at 60-65 degrees C. In each case, refolding required chaperonin 60, chaperonin 10 and ATP, giving up to 80% regeneration of control activity.

Structural similarities between chaperone molecules of the HSP60 and HSP70 families deduced from hydrophobic cluster analysis

In this study, the conservation of strong structural landmarks between all the members of two chaperone families (HSP60 and HSP70) was deduced from their sequences by hydrophobic cluster analysis. On this basis, we propose that the ATP-binding environment is maintained by a similar fold in both protein families. The observed similarities extend throughout the proteins, including both the ATPase domain and the C-terminal substrate-binding domain.

Crystallization and preliminary X-ray investigation of the Escherichia coli molecular chaperone cpn60 (GroEL)

The Escherichia coli molecular chaperone, cpn60 (GroEL), has been purified from an overproducing E. coli strain and crystallized. Of the two crystal forms that were obtained, one was found to be suitable for crystallographic and structural studies at low resolution. Preliminary X-ray investigation of the crystals show unit cell dimensions: a = 143.3, b = 154.6 and c = 265 A, with alpha = 82 degrees, beta = 95 degrees and gamma = 107 degrees. The space group is P1 and the crystals diffract to a maximum of 7 A when using CuK alpha X-rays from a rotating anode. Both electron microscopy and non-denaturing electrophoretic analysis of redissolved cpn60 crystals show that cpn60 crystallizes in the native oligomeric form. Comparison between the dimensions of oligomeric cpn60 and the crystallographic unit cell volume suggests that the unit cell contains two oligomeric cpn60 molecules. The VM value for two cpn60 molecules per unit cell is 3.5 A3/Da, corresponding to a water content of 65%. Electrophoretic analysis under denaturing conditions shows that the cpn60 in crystals is heterogeneous, and this probably explains the limited resolution of the diffraction data.

Molecular cloning, sequencing, and transcriptional analysis of the groESL operon from Bacillus stearothermophilus

Using a gene probe of the Bacillus subtilis groEL gene, a 7.3-kb HindIII fragment of chromosomal DNA of Bacillus stearothermophilus was cloned. Sequencing of 2,309 bp led to the detection of two open reading frames in the order groES groEL. Primer extension studies revealed one potential transcription start site preceding the groESL operon, which was activated upon temperature upshift. Northern blot (RNA) analysis resolved two mRNA species with lengths of 2.2 and 1.5 kb; RNA slot-blot experiments revealed an at least 10-fold increase in the amount of specific mRNA from 0 to 7 min postinduction followed by a decrease. The 9-bp inverted repeat characteristic of many gram-positive bacteria was found within the 5' leader region of the mRNA. The groESL operon of B. stearothermophilus could complement E. coli groES(Ts) and groEL(Ts) mutants for growth at high temperature and for propagation of phage lambda.