Thermal AFM: a thermopile case study

In this work, an atomic force microscope (AFM) with an integrated thermal sensor has been used to obtain the local spatial distribution of temperatures in a micromachined thermopile with submicron resolution. In this communication, we will show how the dimensional, structural and functional characteristics of a thermopile suits well with the requirements for AFM thermal imaging, and how a deeper insight of the thermopile operation can be gained with the aid of these advanced scanning probe-based tools.

A portable forced oscillation device for respiratory home monitoring

The increase in the prevalence of chronic respiratory diseases has resulted in a rise in health services provided at home. The forced oscillation technique (FOT) proves to be a useful tool when it is desired to assess lung function noninvasively, and particularly for patients in whom spirometry cannot be applied. As no portable FOT device is currently available, the aim of this study was to design and test a portable FOT system for ambulatory and home care applications. The system devised is based on a microprocessor, which allows online computation of respiratory resistance (Rrs) and reactance (Xrs) and reliability indices. The portable device was compared with a conventional FOT system by using signals from 14 patients with chronic respiratory disease. This device has the same computation capabilities and flexibility as conventional FOT systems and meets the requirements for home application. Rrs (14.2 +/- 6.0 cmH2O x s x L(-1), mean +/- SD) and Xrs (-5.3 +/- 2.7 cmH2O x s x L(-1)) measured at 5 Hz by the portable system virtually coincided with those computed with the reference conventional FOT system: mean differences +/-SD were 0.074 +/- 0.025 and 0.005 +/- 0.009 cmH2O x s x L(-1), respectively. This portable forced oscillation technique device could be a useful tool for monitoring respiratory mechanics in ambulatory and home care applications.

Occurrence of two architectural types of hexagonal bilayer hemoglobin in annelids: comparison of 3D reconstruction volumes of Arenicola marina and Lumbricus terrestris hemoglobins

A 3D reconstruction at 25 A resolution of native hemoglobin of the polychaete worm Arenicola marina was carried out from frozen-hydrated specimens examined in the electron microscope. The reconstruction volume of this large extracellular multimeric respiratory pigment appears as a hexagonal bilayer structure with eclipsed vertices in its upper and lower hexagonal layers. Conversely, in hemoglobins of oligochaetes, achaetes, and vestimentiferans and in chlorocruorins of the Sabellidae (polychaete) family, the vertices of the upper layer are 16 degrees clockwise rotated with respect to those of the lower layer. The fact that two other polychaete hemoglobins (Alvinella pompejana and Tylorrhynchus heterochaetus) have the same architecture as Arenicola led us to define two types of hexagonal bilayer hemoglobins/chlorocruorins: (i) type-I present in oligochaete, achaete, and vestimentiferan hemoglobins and in Sabellidae chlorocruorins; and (ii) type-II present in polychaete hemoglobins. A comparative study of the hemoglobins of Lumbricus terrestris (type-I) and Arenicola marina (type-II) showed that only two small differences located in the c4 and c5 linking units are responsible of the important architectural difference present in oligomers. A likely scheme proposed to explain the phylogenic distribution of the two types suggests that Clitellata, Sabellida (polychaete), and vestimentiferan hemoglobins and chlorocruorins derive from a type-I ancestral molecule, while Terebellida (Alvinella), Phyllodocida (Tylorrhynchus), and Scolecida (Arenicola) and possibly other polychaetes derive from an ancestor molecule with type-II hemoglobin. The architectures of the hollow globular substructures are highly similar in Arenicola and Lumbricus hemoglobins, with 12 globin chains and three linking units (c3a, c3b, and c4). The central piece of Arenicola hemoglobin is an ellipsoid while that of Lumbricus is a toroid. No phylogenic correlation could be found between the structure of the central pieces and the architecture type.

Expression of brain-derived neurotrophic factor in cortical neurons is regulated by striatal target area

Changes in BDNF expression after different types of brain insults are related to neuroprotection, stimulation of sprouting, and synaptic reorganization. In the cerebral cortex, an autocrine-paracrine mechanism for BDNF has been proposed because the distribution patterns of BDNF and TrkB expression are almost identical. Moreover, cortical BDNF is anterogradely transported to the striatum, suggesting a role of BDNF in the functional interaction between the two brain regions. Here we have examined the expression of this neurotrophin in the cerebral cortex after various striatal lesions. Intrastriatal injection of quinolinate, kainate, 3-nitropropionic acid, or colchicine increased BDNF mRNA levels in cerebral cortex. In contrast, stimulation of neuronal activity in the striatum did not change cortical BDNF expression. Both excitatory amino acids increased BDNF expression in neurons of cortical layers II/III, V, and VI that project to the striatum. Moreover, grafting a BDNF-secreting cell line prevented both the loss of striatal neurons and the cortical upregulation of BDNF induced by excitotoxins. Because retrograde transport in the corticostriatal pathway was intact after striatal lesions, our results suggest that striatal damage upregulates endogenous BDNF in corticostriatal neurons by a transneuronal mechanism, which may constitute a protective mechanism for striatal and/or cortical cells.

Neurturin protects striatal projection neurons but not interneurons in a rat model of Huntington's disease

Glial cell line-derived neurotrophic factor and neurturin are neurotrophic factors expressed in the striatum during development and in the adult rat. Both molecules act as target-derived neurotrophic factors for nigrostriatal dopaminergic neurons. While glial cell line-derived neurotrophic factor has also been described to have local trophic effects on striatal neurons, the effects of neurturin in the striatum have not yet been described. Here we examine whether neurturin protects striatal projection neurons (calbindin-positive) and interneurons (parvalbumin- or choline acetyltransferase-positive) in an animal model of Huntington's disease. A fibroblast cell line engineered to over-express neurturin was grafted into adult rat striatum 24h before quinolinate injection. In animals grafted with a control cell line, intrastriatal quinolinate injection reduced the number of calbindin-, parvalbumin- and choline acetyltransferase-positive neurons, seven days post-lesion. Intrastriatal grafting of neurturin-secreting cells protected striatal projection neurons, but not interneurons, from quinolinate excitotoxicity. This effect was much more robust than that reported previously for a glial cell line-derived neurotrophic factor-secreting cell line on striatal calbindin-positive neurons. However, intrastriatal grafting of glial cell line-derived neurotrophic factor- but not neurturin-secreting cells prevented the decrease in choline acetyltransferase activity induced by quinolinate injection. Taken together, our results show that neurturin- and glial cell line-derived neurotrophic factor-secreting cell lines have clearly differential effects on striatal neurons. Grafting of the neurturin-secreting cell line showed a more specific and efficient trophic effect on striatal projection neurons, the neuronal population most affected in Huntington's disease. Therefore, our results suggest that neurturin is a good candidate for the treatment of this neurodegenerative disorder.

Phenotypic testing predicts virological response in successive protease inhibitor-based regimens

OBJECTIVE

To evaluate the importance of the number of active drugs, as determined by phenotypic resistance testing, in achieving virological response in successive salvage regimens.

DESIGN

Phenotypic study of 57 plasma samples corresponding to 24 patients who had sequentially received three protease inhibitor-containing regimens. Phenotypic susceptibility to a drug (active drug) was defined as less than a four-fold-increase in the IC50 in comparison with the wild type.

MAIN OUTCOME MEASURE

Virological response according to the number of active drugs (three versus two or fewer), HIV load, length of antiretroviral exposure, and line of protease inhibitor-based therapy (first, second and third regimen).

RESULTS

Before the first protease inhibitor-based therapy, the median time on antiretroviral treatment was 42 months, and before the second and third protease inhibitor-salvage regimens it was 10 and 8 months, respectively. The number of patients receiving three active drugs simultaneously was 24, 35 and 31% in each line of therapy. At week 12, a close correlation was found between the presence of three active drugs in the antiretroviral regimen and the rate of virological response, in comparison with those patients receiving two or fewer active drugs [76 versus 45%, relative risk (RR), 1.7; 95% confidence interval (CI) 1.1-2.6; P = 0.028]. In a multivariate analysis, the use of two or fewer active drugs was an independent predictor of lack of response, regardless of HIV load, length of previous antiretroviral exposure and line of salvage therapy (RR, 4.5; 95%CI, 1.1-18.3; P = 0.03). Of note, a higher rate of response was observed in patients receiving the first protease inhibitor-containing regimen in comparison with those in subsequent protease inhibitor-based salvage regimens (83 versus 50 versus 28%, P < 0.01), even when only those patients receiving three active drugs were included (100 versus 71 versus 60%).

CONCLUSIONS

This data confirm the usefulness of phenotypic testing in guiding antiretroviral therapy in heavily pretreated patients. The number of active drugs and the line of salvage therapy are independent predictors of virological response, regardless of HIV load and the length of antiretroviral exposure.

Polymerization of bacteriophage T4 tail sheath protein mutants truncated at the C-termini

Gene 18 of bacteriophage T4 encodes the contractile protein of the tail sheath. Previous work has shown that the full-length recombinant gene product (gp) 18 of 658 amino acid residues assembles in Escherichia coli cells into a long polysheath structure. However, the gp18 mutants truncated at the N-termini form insoluble aggregates similar to inclusion bodies. In this study, six plasmid vectors expressing the recombinant gp18 proteins truncated at the C-termini have been constructed. The CDelta58, CDelta129, CDelta152, C[g1]72, CDelta248, and CDelta287 proteins contain 600, 529, 506, 486, 410, and 371 residues of the full-length gp18 molecule, respectively. All the recombinant proteins were soluble and, except for the CDelta287 mutant, were assembled into polysheath-related structures. Electron microscopy of negatively stained purified proteins was performed and the resulting images were analyzed by computing their Fourier transforms. The CDelta58 and CDelta129 mutants, in addition to forming common contracted-type polysheath structures, assembled into thinner filaments that we called "noncontracted polysheaths" (NCP). The CDelta152, CDelta172, and CDelta248 proteins assembled into the NCP type only. Image processing showed that the NCP filaments significantly differ from both extended sheaths of T4 particle and polysheaths. The structure of the NCP filaments might correspond to the transitional helices postulated by Moody (J. Mol. Biol., 1973, 80, 613-636) that appeared during the process of tail contraction. Our results suggest that a short region at the C-terminus of the CDelta129 protein determines the contractile properties of the gp18 molecule. The shortest, the CDelta287 protein, does not assemble into regular structures, thus indicating that a sequence's stretch at the C-end of the CDelta248 mutant might be responsible for polymerization of gp18.

Mitochondrial localization and oligomeric structure of HClpP, the human homologue of E. coli ClpP

A bacterially expressed recombinant HClpP protein, the human homologue of Escherichia coli ClpP protease, was used to obtain specific polyclonal antibodies. Those antibodies identify a 26 kDa polypeptide in mitochondrial subcellular fractions of rat and human liver. Immunofluorescence and electron microscopic studies demonstrate that the mammalian homologue of ClpP is located in the mitochondrial matrix with a tendency to be found in association with the inner mitochondrial membrane. An HClpP recombinant protein with a truncated NH2terminus (missing the first 58 amino acid residues) shows a molecular mass of 26 kDa under denaturing conditions. This N-truncated HClpP recombinant protein shows a native molecular mass of 340 kDa that is identical with the native molecular mass of the partially purified protein from rat liver mitochondria. Electron microscopy shows that the N-truncated recombinant HClpP has a ring shape with seven identical morphological units in the periphery, exhibiting a 7-fold symmetry. The native molecular mass and the electron microscopic studies suggest that mitochondrial ClpP is composed of two heptameric rings with 7-fold symmetry, similar to E. coli ClpP.

Oligomeric structures of the phage phi29 histone-like protein p6

Protein p6 of Bacillus subtilis phage phi29 has been described as a histone-like protein, playing a role in genome organization and compaction, on the basis of its high intracellular abundance, its pleiotropic effect, and its ability to bind and highly compact the whole phi29 DNA in vitro. Protein p6 forms large multimeric nucleoprotein complexes in which a right-handed superhelical DNA wraps toroidally around the protein core. Analytical ultracentrifugation analysis, at the concentration estimated in vivo (at least 1 mM), showed that protein p6 self-associates into elongated oligomers, suggesting that, in the absence of DNA, the protein could form a scaffold for DNA binding. In this work we have studied the structure of these oligomers by transmission electron microscopy and image processing. The results show that protein p6 aggregates into crooked-shaped oligomers, compatible with a helical structure. The oligomers could interact head-to-tail to form doughnut-shaped structures or they could grow into right-handed double-helical filaments by a nucleation-dependent polymerization process. The dimensions of the crooked-shaped structures are in agreement with that of the DNA in the nucleoprotein complex previously described. We propose that the crooked-shaped structures could act as a scaffold imposing the right-handed path followed by the DNA, and thus it could be considered a non-transient DNA chaperone.

The neurotrophin receptors trkA, trkB and trkC are differentially regulated after excitotoxic lesion in rat striatum

In the present work, we examined the time-dependent changes in trkA, trkB and trkC mRNA levels induced by the injection of glutamate receptor agonists into the striatum. Changes in trk mRNAs induced by quinolinate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), kainate or 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) were analyzed by a ribonuclease protection assay. All high-affinity neurotrophin receptors showed differential regulation after intrastriatal injury. Up-regulation of trkA expression was observed in kainate- or ACPD-injected striata at 10 and 24 h, respectively, whereas quinolinate injection induced down-regulation between 4 and 6 h after injury. Interestingly, all the excitatory amino acid receptor agonists induced up-regulation of trkB-kinase mRNA levels. This increase was maximal between 2 and 4 h after injection except in kainate injected striata, which showed the peak of expression at 10 h. In contrast, no changes in trkC mRNA expression were observed after striatal excitotoxic injury. In conclusion, our results show that trk receptor mRNA levels are differentially regulated by excitatory amino acid receptor agonists in the striatum, suggesting that changes in the levels of neurotrophin receptors might be involved either in synaptic plasticity processes or in neuronal protection in the striatal excitotoxic paradigm.

Intrastriatal grafting of a GDNF-producing cell line protects striatonigral neurons from quinolinic acid excitotoxicity in vivo

Glial cell line-derived neurotrophic factor (GDNF) is a neurotrophic factor with a therapeutic potential in neurodegenerative disorders. GDNF is expressed in the adult striatum, but its signalling tyrosine kinase receptor, c-ret, has not been detected in this structure by in situ hybridization. In the present work, we first examined c-ret and GDNF receptor alpha 1 (GFR-alpha 1) expression using an RNAse protection assay, and found that both receptors are expressed in the adult rat striatum. We then examined whether GDNF was able to regulate the phenotype and/or prevent the degeneration of striatal projection neurons in a well-characterized model of excitotoxic damage. A fibroblast cell line, engineered to overexpress GDNF, was grafted in adult rats striatum 24 h before quinolinic acid (QUIN) injection. QUIN injection alone or in combination with the control cell line induced a loss of glutamic acid decarboxylase 67 (GAD)-, preprotachykinin A (PPTA)-, prodynorphin (DYN)- and preproenkephalin (PPE)-positive neurons. GDNF selectively prevented: (i) the loss of a subpopulation of striatonigral neurons expressing GAD and PPTA; (ii) the atrophy of PPTA-positive neurons; and (iii) the decrease in GAD, PPTA and DYN mRNA expression, after QUIN injection. Moreover, in unlesioned animals, GDNF increased the size of PPTA-positive neurons and up-regulated their mRNA levels. In contrast, GDNF showed no effect in intact or lesioned striatopallidal PPE-positive neurons. Thus, our findings show that GDNF selectively regulates the phenotype and protects striatonigral neurons from QUIN-induced excitotoxicity, suggesting that GDNF may be used for the treatment of striatonigral degenerative disorders, e.g. Huntington's disease and multiple system atrophy.

Differential regulation of the expression of nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 after excitotoxicity in a rat model of Huntington's disease

In the present study we have evaluated changes in nerve growth factor (NGF), brain-derived neurotrophic factor, and neurotrophin 3 (NT-3) mRNA expression induced by different glutamate receptor agonists injected into the neostriatum. Up-regulation of NGF expression was observed at 24 h after intrastriatal quinolinate injection, an N-methyl-D-aspartate receptor agonist, and this increase was maintained up to 7 days after lesion. NGF up-regulation was also apparent in alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) treatment from 6 to 16 h postinjection. Instead, BDNF was up-regulated only at 6 h after kainate or AMPA excitotoxicity. Interestingly, NT-3 mRNA was down-regulated from 10 to 16 h following AMPA lesion, while 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid injection enhanced NT-3 mRNA levels at 10 h. Our results show a specific neurotrophin response induced by stimulation of each glutamate receptor. These activity-dependent changes might be involved in neuronal plasticity processes and may underlie the differential vulnerability of striatal neurons observed in neurodegenerative disorders.

Optimization of phosphorus localization by EFTEM of nucleic acid containing structures

Energy Filtered Transmission Electron Microscopy (EFTEM) has been used to study nucleic acids localization in unstained thin sections of virus-infected cells. For this purpose, phosphorus maps (P-maps) have been obtained by applying the N-windows Egerton model for background subtraction from data acquired by a non-dedicated TEM Jeol 1200EXII equipped with a post-column PEELS Gatan 666-9000 and a Gatan Image Filter (GIF-100). To prevent possible errors in the evaluation of elemental maps and thus incorrect nucleic acid localization, we have studied different regions of swine testis (ST) cells with similar local density containing either high concentration of nucleic acids (condensed chromatin and ribosomes) or a very low concentration (mitochondria). Special care was taken to optimize the sample preparation conditions to avoid as much as possible the traditional artifacts derived from this source. Selection of the best set of pre-edge images for background fitting was also considered in order to produce "true P-maps". A new software for interactive processing of images series has been applied to estimate this set. Multivariate Statistical Analysis was used as a filtering tool to separate the "useful information" present in the inelastic image series (characteristic signal) from the "non-useful information" (noise and acquisition artifacts). The reconstitution of the original image series preserving mainly the useful information allowed the computation of P-maps with improved signal-to-noise ratio (SNR). This methodology has been applied to study the RNA content of maturation intermediate coronavirus particles found inside infected cells.

ATP binding induces large conformational changes in the apical and equatorial domains of the eukaryotic chaperonin containing TCP-1 complex

The chaperonin-containing TCP-1 complex (CCT) is a heteromeric particle composed of eight different subunits arranged in two back-to-back 8-fold pseudo-symmetric rings. The structural and functional implications of nucleotide binding to the CCT complex was addressed by electron microscopy and image processing. Whereas ADP binding to CCT does not reveal major conformational differences when compared with nucleotide-free CCT, ATP binding induces large conformational changes in the apical and equatorial domains, shifting the latter domains up to 40 degrees (with respect to the inter-ring plane) compared with 10 degrees for nucleotide-free CCT or ADP-CCT. This equatorial ATP-induced shift has no counterpart in GroEL, its prokaryotic homologue, which suggests differences in the folding mechanism for CCT.

Symmetric GroEL-GroES complexes can contain substrate simultaneously in both GroEL rings

Incubation of rhodanese with hche aperonins GroEL and GroES (1:2 GroEL14:GroES7 molar ratio) under functional and steady state conditions for ATP leads to the formation of a high proportion of rhodanese-bound symmetric complexes (GroEL14(GroES7)2), as revealed by native electrophoresis. Aliquots of such samples were observed under the electron microscope, and the symmetric particles were classified using neuronal networks and multivariate statistical analysis. Three different populations of symmetric particles were obtained which contained substrate in none, one or both GroEL cavities, respectively. The presence of substrate in the symmetric complexes under functional conditions supports their role as active intermediates in the protein folding cycle. These results also suggest that symmetric GroEL-GroES complexes can use both rings simultaneously for folding, probably increasing the efficiency of the reaction.

Conformational changes in the GroEL oligomer during the functional cycle

The conformational changes that the GroEL oligomer undergoes upon nucleotide and cochaperonin GroES binding have been studied using electron microscopy and image processing techniques. Average side views of the three allosteric states (TT, TR, and RR, which correspond to none, one, or both of the two heptameric rings of the GroEL oligomer occupied by nucleotide, respectively) of GroEL and GroEL-GroES complexes for ADP, ATP, and two nonhydrolyzable analogs (AMP-PNP and ATP gamma S) have been obtained at 20-25 A resolution. Both AMP-PNP and ATP induce similar conformational shifts in the apical domains of GroEL. At the TR state, only one of the GroEL rings shows an upward and outward movement of the apical domains ("open state"). At the RR state for AMP-PNP and ATP, both GroEL rings undergo conformational changes, albeit of different magnitude, giving rise to a structurally asymmetric particle (one ring in the "open" state, while the other is in an "intermediate" state). These changes are also observed when GroEL is incubated with ADP and Pi, but not with ADP, which suggests that upon ATP binding, GroEL undergoes a conformational change that is partly maintained after ATP hydrolysis and as long as ADP and Pi are bound to the GroEL ring. The conformational changes undergone by GroEL are discussed within the framework of a proposed GroEL cycle mechanism.

Xmipp: An Image Processing Package for Electron Microscopy

We present in this article a specialized suite of image processing programs primarily aimed at obtaining the three-dimensional reconstruction of biological specimens from large sets of projection images obtained by transmission electron microscopy. The programs are written in ANSI-C and use X-Windows for graphical output. A number of parallel extensions using PVM and PARMACS are provided. The programs are freely available by anonymous ftp at ftp.cnb.uam.es.

Compliance with pharmacologic prophylaxis and therapy in bronchial asthma

Between January 1 and December 31, 1988, 288 children [185 boys and 103 girls, mean age 8.75 +/- 4.98 years (range 2.50 to 16.83)], followed at the Outpatient Clinic for Lung Diseases of the University of Milan 5th Pediatric Department, were interviewed blindly in order to assess their compliance with pharmacologic therapy. All children were suffering from episodic, frequent, or chronic asthma requiring therapy as needed and preventive drugs for at least 30 days. Prophylaxis (including cromolyn, beclomethasone, theophylline retard, ketotifen, oxatomide, albuterol, and prednisone, alone or in combinations) and therapy in case of symptoms (albuterol, with or without theophylline prompt or beclomethasone) were prescribed. A study questionnaire was completed 30 to 45 days after the prescription with no advance warning by a physician unaware of the prophylactic and therapeutic prescriptions. Out of the 288 patients, 31 (10.8%) failed to return for the second visit. Understanding of prophylaxis was full in 61.1% of cases, partial in 23.3% and nil in 4.9%. Therapy as needed was fully remembered by 77.1% of parents, partially by 9.4% and totally forgotten by 2.8%. Compliance with single-drug prophylaxis was full in 60.1% of cases, partial in 22.2% and nil in 6.4%. Statistical analysis showed compliance was significantly better for ketotifen than for disodium cromoglycate (chi squared 9.85, P < .02), for ketotifen than for theophylline (chi squared 9.98, P < .02), and for beclomethasone than for theophylline (chi squared 8.77, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Reversible interaction of beta-actin along the channel of the TCP-1 cytoplasmic chaperonin

The cytoplasm of eukaryotes contains a heteromeric toroidal chaperonin assembled from the t-complex TCP-1 and several other related polypeptides. The structure of the TCP-1 cytoplasmic chaperonin and that of the binary complex formed between this chaperonin and unfolded beta-actin have been studied using electron microscopy and image processing techniques. Two-dimensional averaging of front views reveals a circular stain-excluding mass surrounding a central stain-penetrating region in which the stain is excluded upon actin binding. Sections of a three-dimensional reconstruction of the chaperonin show that the inner core is an empty channel that becomes filled upon binary complex formation with unfolded beta-actin. Upon incubation with Mg-ATP, the beta-actin:chaperonin complex discharges the actin such that the chaperonin central cavity reappears. Side views from different forms of TCP-1 reveals that upon Mg-ATP binding, the cytoplasmic chaperonin undergoes a structural rearrangement that is confirmed using a new classification method.

The formation of symmetrical GroEL-GroES complexes in the presence of ATP

The incubation of chaperonins cpn60 (GroEL) and cpn10 (GroES) from E. coli in the presence of Mg-ATP and KCl generates the formation, as revealed by electron microscopy, of GroEL-GroES complexes with a symmetrical shape in which one toroidal GroES oligomer is bound to each end of the tetradecameric GroEL aggregate (1:2 GroEL:GroES oligomer molar ratio). The symmetrical complexes are not observed in the presence of ADP or the non-hydrolyzable ATP analog, ATP gamma S, where only asymmetrical complexes (1:1 GroEL:GroES oligomer molar ratio) are formed. These results suggest that ATP hydrolysis is required for the formation of symmetrical complexes.

The molecular chaperone TF55. Assessment of symmetry

TF55-like factor from Sulfolobus solfataricus was purified to homogeneity and analyzed by electron microscopy and image analysis to determine the symmetries of these particles. Three different procedures were used to analyze the electron micrographs: (1) fuzzy-set based classification of the particles according to their rotational power spectra; (2) multivariate statistical analysis based on singular value decomposition; (3) circular harmonic analysis. Averages obtained from the three methods show unequivocally that the TF55-like complex presents a 9-fold symmetry.

A structural model for the GroEL chaperonin

Individual particle analysis of end views from negatively stained specimens of purified GroEL from Escherichia coli showed the presence of two different particle populations, those with a six-fold symmetry and those with a seven-fold symmetry, when studied at pH 7.7 and 5.0. Image processing of particles from frozen-hydrated specimens revealed at both pH values a homogeneous population of particles with a strong seven-fold symmetry component and an average image with seven asymmetric units. Biochemical analysis of purified GroEL showed unequivocally the presence of a single polypeptide with the N-terminal sequence identical to that of GroEL. These results are compatible with a structural model of GroEL as an asymmetric aggregate built up by two rings of seven-fold and six-fold symmetries, respectively.

Streptomyces lividans possesses a GroEL-like chaperonin

Streptomyces lividans grown at 45 degrees C produces a GroEL-like chaperonin. This protein is specifically synthesized in bacterial cell cultures upon heat shock induction. It has a similar size (62 kDa) to the GroEL-like proteins from Escherichia coli and Bacillus subtilus and shows immunological cross-reaction with serum raised against GroEL from E. coli. The S. lividans 62-kDa protein assembles into oligomers around 20S that show a morphology consistent with a barrel showing six-fold and seven-fold symmetries as previously described in E. coli and B. subtilis.