Cryo-atomic force microscopy of smooth muscle myosin

The motor and regulatory domains of the head and the 14-nm pitch of the alpha-helical coiled-coil of the tail of extended (6S) smooth-muscle myosin molecules were imaged with cryo atomic force microscopy at 80-85 K, and the effects of thiophosphorylation of the regulatory light chain were examined. The tail was 4 nm shorter in thiophosphorylated than in nonphosphorylated myosin. The first major bend was invariant, at approximately 51 nm from the head-tail junction (H-T), coincident with low probability in the paircoil score. The second major bend was 100 nm from the H-T junction in nonphosphorylated and closer to a skip residue than the bend (at 95 nm) in thiophosphorylated molecules. The shorter tail and distance between the two major bends induced by thiophosphorylation are interpreted to result from melting of the coiled-coil. An additional bend not previously reported occurred, with a lower frequency, approximately 24 nm from the H-T. The range of separation between the two heads was greater in thiophosphorylated molecules. Occasional high-resolution images showed slight unwinding of the coiled-coil of the base of the heads. We suggest that phosphorylation of MLC20 can affect the structure of extended, 6S myosin.

[In situ DNA labeling apoptosis in breast cancer as related to prognosis]

OBJECTIVE

This study was undertaken to determine the expression of apoptosis in breast cancer and to evaluate it's significance as a prognostic marker.

METHODS

A series of 91 invasive breast cancer was analysed for the expression of apoptosis by using the 3-end-labeling method of DNA in tissue sections. The apoptotic indexes were the percentages of apoptotic cells among tumor cells.

RESULTS

The end-labeling method allowed a precise evaluation of the expression of apoptosis. Apoptosis occurred in 91.2% of breast cancer patients, and apoptotic indexes were divided into two groups, 0-0.21 and 0.28-0.62. Low apoptotic index was related to axillary lymph node metastasis (P < 0.01). In survival analysis, higher apoptotic index was related to disease free survival (P = 0.0095) and overall survival (P = 0.0348) in the entire cohort. Cox's analysis showed apoptotic index had no independent prognostic value.

CONCLUSION

The apoptosis was a spontaneous phenomenon in breast cancer tissue, and the expression was different from each other. Further analysis was needed to clarify the relationship between apoptosis and prognosis, especially the response to adjuvent therapy.

Immobilization of glucose oxidase with the blend of regenerated silk fibroin and poly(vinyl alcohol) and its application to a 1,1'-dimethylferrocene-mediating glucose sensor

The structure and properties of the blend of regenerated silk fibroin (RSF) and poly(vinyl alcohol) (PVA) were investigated. The two polymers in the blend are in the state of phase segregation. Infrared (IR) spectra indicate that the RSF in the blend maintains its intrinsic properties, thus, ethanol treatment can transfer silk I structure of RSF to silk II structure. The water absorption property and mechanical property of the blend are improved in comparison with those of RSF. The blend maintains the major merit of RSF, that is, it can immobilize glucose oxidase on the basis of the conformational transition from silk I structure to silk II structure. The properties of the immobilized enzyme are examined. Moreover, the second generation of glucose sensor based on the immobilized enzyme is fabricated and it has a variety of advantages including easy maintenance of enzyme, simplicity of construction, fast response time and high stability.

[Study on the immunophenotype of myeloid cells in myelodysplastic syndromes and its clinical implications]

OBJECTIVE

To explore the immunophenotype of myeloid cells in myelodysplastic syndromes and its clinical implications.

METHODS

A panel of monoclonal antibodies was used to detect CD13, CD33, CD15 and CD14 on the membrane surfaces of myeloid cells in the bone marrow from 51 patients with myelodysplastic syndromes (MDS), 21 with aplastic anemia (AA), 21 with paroxysmal nocturnal hemoglobinuria (PNH), and 15 normal subjects, by immunoenzymatic assay. The morphology and chromosome karyotype of bone marrow cells of MDS patients were also examined.

RESULTS

CD14+ cells, CD13+ cells and CD33+ cells in the bone marrow were more in MDS patients than in normal controls, AA patients and PNH patients. CD15+ cells in the bone marrow were less in MDS patients than in normal controls. The percentages of CD14, CD13 and CD33 positive cells in the bone marrow of MDS patients were related to the percentage of myeloblast, the chromosomal aberrations and the response to treatment.

CONCLUSION

There was an immunophenotypic misexpression of myeloid cells in MDS patients. Immunophenotype analysis of myeloid cells might be useful for the diagnosis and directing treatment in MDS patients.

Biological cryo atomic force microscopy: a brief review

Despite many successes, atomic force microscopy (AFM) of biological specimens at room temperature is still severely limited by at least two factors: the softness and the thermal motion of flexible multi-domain/subunit molecules. Both problems can be overcome by imaging biological structures at cryogenic temperatures. Even though the instrumentation is considerably more complex and earlier attempts were largely unsuccessful, cryo-AFM has recently been demonstrated on a number of biological specimens, using an AFM operated in liquid nitrogen vapor under ambient pressure. In this brief review, both the method of instrumentation and the latest biological applications are discussed. Not only has the cryo-AFM attained high resolution on those specimens that could not be well imaged at room temperature, but it has also produced potentially important information on several specimens. These results firmly establish the cryo-AFM as a useful and versatile structural probe in biology with its own unique capabilities.

Inhibition of spontaneous apoptosis in human breast cancer

Breast tumorigenesis proceeds through an accumulation of specific genetic alteration. Breast malignant transformation is dependent on not only the rate of cell production but also on apoptosis, a genetically programed process of autonomous cell death. We investigated whether breast tumorigenesis involved an altered susceptibility to apoptosis and proliferation by examining normal breast epithelium and breast cancer samples. We found there is a great inhibition of spontaneous apoptosis in breast cancer cells compared with normal breast epithelium. The inhibition of apoptosis in breast cancer may contribute to neoplastic transformation.

Different balance of excitation and inhibition in forward and feedback circuits of rat visual cortex

Different cortical areas are linked reciprocally via forward and feedback connections. Forward connections are involved in the representation of retinal images, whereas feedback pathways may play a role in the selection and interpretation of visual information. To examine the synaptic mechanisms of forward and feedback connections between primary and secondary visual cortical areas directly, we have performed intracellular recordings in slices of rat visual cortex. Irrespective of stimulus intensity and membrane potential, 78% (45/58) of the cells in striate cortex activated by feedback input showed monosynaptic responses that were depolarizing only, and inhibitory inputs were evident merely as a slight acceleration in the decay of EPSPs. In contrast, in 89% (17/19) of the cells, stimulation of forward input evoked monosynaptic excitatory postsynaptic potentials (EPSPs), followed by disynaptic, hyperpolarizing inhibitory postsynaptic potentials (IPSPs). EPSPs followed by IPSPs also were recorded after stimulation of local connections within primary visual cortex (92%, 12/13) and after activation of thalamocortical input (91%, 10/11). These results suggest that the synaptic organization of feedback connections are distinct from forward, local, and thalamocortical circuits. The findings further indicate that intracortical back projections exert modulatory influences via synaptic mechanisms in which weak inhibitory input is strongly dominated by excitation.

Inhibition of apoptosis in human breast cancer as related to prognosis

Breast tumorigenesis proceeds through an accumulation of specific genetic alterations. Breast malignant transformation is dependent on not only the rate of cell production but also on apoptosis, a genetically programmed process of autonomous cell death. It may also be important in the overall growth dynamics of neoplastic cells, both in the natural history and when they are exposed to chemotherapy or radiation. This study evaluated the biological and clinical implications of spontaneous apoptosis in human breast cancer. Apoptosis was measured in 8 normal breast tissues and 91 human breast cancer samples by Apoptag end labeling method. We found there was a significant inhibition of spontaneous apoptosis in breast cancer cells compared with normal breast epithelium. In 91 breast cancer samples, apoptotic index (AI) was strongly associated with lymph node metastasis; Low apoptosis of tumor cells was more frequent in poorly differentiated tumors and has a poor outcome.

[Growth inhibitory effect of retinoic acid in human breast cancer cells correlates with retinoic acid receptor alpha (RAR alpha) expression]

The relationship between the effect of retinoic acid (RA) on the growth of breast cancer cell and their estrogen receptor (ER) status as well as the relationship between RA effect and the expression of retinoic acid receptorsd (RAR alpha) were studied by cell growth assay, Northern Blot and gene transfection. It was found that RA could only inhibit the growth of ER-positive but not ER-negative breast cancer cells. RAR alpha mRNA level was significantly higher in ER-positive breast cancer cell lines than that in ER-negative breast cancer cell line. The expressions of other subtypes of RAR in ER-positive cells were not significantly different from those in ER-negative ones. When, RAR alpha cDNA was introduced and ixpressed in RA-resistant, ER-negative MDA-MB-231 breast cancer cell line, its growth was strongly inhibited by RA. These results indicate that RAR alpha plays a major role in the retinoi-dmediated inhibition of growth in human breast cancer cells.

Chaperonins GroEL and GroES: views from atomic force microscopy

The Escherichia coli chaperonins, GroEL and GroES, as well as their complexes in the presence of a nonhydrolyzable nucleotide AMP-PNP, have been imaged with the atomic force microscope (AFM). We demonstrate that both GroEL and GroES that have been adsorbed to a mica surface can be resolved directly by the AFM in aqueous solution at room temperature. However, with glutaraldehyde fixation of already adsorbed molecules, the resolution of both GroEL and GroES was further improved, as all seven subunits were well resolved without any image processing. We also found that chemical fixation was necessary for the contact mode AFM to image GroEL/ES complexes, and in the AFM images. GroEL with GroES bound can be clearly distinguished from those without. The GroEL/ES complex was about 5 nm higher than GroEL alone, indicating a 2 nm upward movement of the apical domains of GroEL. Using a slightly larger probe force, unfixed GroEL could be dissected: the upper heptamer was removed to expose the contact surface of the two heptamers. These results clearly demonstrate the usefulness of cross-linking agents for the determination of molecular structures with the AFM. They also pave the way for using the AFM to study the structural basis for the function of GroE system and other molecular chaperones.

Imaging biological structures with the cryo atomic force microscope

It has long been recognized that one of the major limitations in biological atomic force microscopy (AFM) is the softness of most biological samples, which are easily deformed or damaged by the AFM tip, because of the high pressure in the contact area, especially from the very sharp tips required for high resolution. Another is the molecular motion present at room temperature due to thermal fluctuation. Using an AFM operated in liquid nitrogen vapor (cryo-AFM), we demonstrate that cryo-AFM can be applied to a large variety of biological samples, from immunoglobulins to DNA to cell surfaces. The resolution achieved with cryo-AFM is much improved when compared with AFM at room temperature with similar specimens, and is comparable to that of cryo-electron microscopy on randomly oriented macromolecules. We will also discuss the technical problems that remain to be solved for achieving even higher resolution with cryo-AFM and other possible applications of this novel technique.

Retinoic acid nuclear receptor alpha(RAR alpha) plays a major role in retinoid-mediated inhibition of growth in human breast carcinoma cells

Retinoids mediate their actions via retinoic acid receptors (RARs) and retinoid X receptors (RXRs). Each of class of these nuclear retinoid receptor is further subdivided into three species namely alpha, beta and gamma. Recently studies demonstrated that estrogen receptor (ER)-positive human breast cancer (HBC) cell lines are sensitive and ER-negative cell lines are resistant to growth inhibitory effects of retinoic acid (RA). In this study, we found that only RAR alpha mRNA levels was strongly correlated with ER-status. To further investigate the major role of RAR alpha in retinoid-mediated inhibition of growth, we transfected RAR alpha cDNA into two RA-resistant ER-negative HBC cell lines. Analysis of different clonal populations of RAR alpha transfectants from each cell line revealed growth inhibition by retinoids. Our results demonstrated that RAR alpha plays a major role in mediating retinoids inhibition of growth in HBC cells and adequate levels of RAR alpha are required for such an effect.

[Retinoic acid nuclear receptor beta (RAR beta) inhibits breast carcinoma growth]

Retinoids are capable of modulating cellular differentiation and proliferation. Retinoids mediate gene function through a series of nuclear receptors. The retinoic acid receptor beta (RAR beta) has been shown to play an important role in the differentiation of a number of cell types. RAR beta is either absent or expressed at extremely low levels in a number of tumor types including breast carcinoma. It was demonstrated that transfection of RAR beta gene in breast carcinoma cell with its subsequent expression resulted in inhibition of cell growth. Retinoic acid significantly inhibited monolayer growth of the breast carcinoma cells expressing RAR beta, while it had no effect on the growth of the control cells. The RAR beta expressing cells formed much smaller and fewer colonies in soft agar and were significantly less tumorigenic in nude mice than the controls. These results suggest that RAR beta may function as a tumor suppressor in breast carcinoma cells.

Engineering new functions and altering existing functions

Structural and mechanistic information, sequence comparisons, and site-directed mutagenesis data continue to provide a basis for the rational design of new protein functions and the alteration of existing functions. Random mutagenesis and 'directed evolution' approaches, however, are making significant headway in solving protein engineering problems, proving highly practical for tuning properties such as enzyme substrate specificity.

Precise and versatile formula for birefringent filters

In an investigation of extraordinary- (E-) ray behavior and the index of refraction for E waves in a uniaxial crystal, a precise and versatile formula for birefringent filters, based on the exact construction of the optical path difference, is set up with neither the approximation Δn = n(o) - n(e) ≤ (or n(e)), nor the ambiguity sin(θ)sin(r(ω)) = n(e). The exact construction gives the correct variation of the position and the dimension in each path, yielding the path difference while the filter is tuning. The formula is applicable not only to a filter with its optical axis parallel to the entrance surface (PAPS) but also to a filter with its axis inclined to the surface (PAIS). Also, the formula indicates that a FAIS allows laser wavelengths to be tuned over a wider range than does a FAPS. The origin of the wider range is interpreted to be the greater variation in the index for the FAIS while the filter is tuning. With the help of the formula we design a FAIS for tuning a cw Ti:sapphire laser.

The effect of deformation on the lateral resolution of atomic force microscopy

A computer model based on the elastic properties of rubber is introduced for the evaluation of the lateral resolution in atomic force microscopy of deformable specimens. The computational results show that, if the full width at half-height can be defined as the lateral resolution, it is continuously improved at greater probe forces, at the expense of a reduced molecular height, In fact, even for a probe that is bigger than the molecule, the real size of the molecule can be 'recovered' at about 25% compression. This result demonstrates that for a better lateral resolution, a greater probe force can be beneficial, provided that the molecule is not moved or damaged and the response remains elastic. Measurements on isolated low-density lipoproteins (LDL) show that with 26% vertical compression, the lateral size measured in atomic force microscopy is only 72% of the value predicted by a simple convolution, and is only slightly larger (approximately 13%) than the known size of LDL. Therefore, the results on LDL provide a direct support for the conclusions of the computational model.

Laser demonstration of diode-laser-pumped neodymium-doped strontium fluorovanadate

The laser properties of diode-laser-pumped neodymium-doped strontium fluorovanadate samples cut perpendicular to the x(a) and y axes have been investigated. A slope efficiency of 36% for the 1.065-µm laser line and a lasing threshold of 6.8 mW have been measured for the x(a)-axis-cut crystal. Data are also presented for the laser's performance as a function of crystal temperature and for the variation of the central peak wavelength with the incident pump power.

Reperfusion injury on cardiac myocytes after simulated ischemia

The extent of cardiac injury incurred during reperfusion as opposed to that occurring during ischemia is unclear. This study tested the hypothesis that simulated ischemia followed by simulated reperfusion causes significant "reperfusion injury" in isolated chick cardiomyocytes. Cells were exposed to hypoxia, hypercarbic acidosis, hyperkalemia, and substrate deprivation for 1 h followed by 3 h of reperfusion. Irreversible cell membrane injury, measured by propidium iodide uptake, increased from 4% of cells at the end of ischemia to 73% after reperfusion; death occurred in only 17% of cells kept ischemic for 4 h. Lactate dehydrogenase release was consistent with these changes. Lengthening ischemia from 30 to 90 min increased cell injury as expected, but of the total cell death, > 90% occurred during reperfusion. "Chemical hypoxia" composed of cyanide (2.5 mM) plus 2-deoxyglucose augmented injury before reperfusion compared with simulated ischemia. Inhibition of oxygen radical generation by use of metal chelator 1,10-phenanthroline reduced cell death from 73% to 40% after reperfusion (P = 0.001). We conclude that simulated reperfusion significantly augments the cellular membrane damage elicited by simulated ischemia in isolated cardiomyocytes devoid of other factors and suggest that reactive oxygen species, perhaps from the mitochondria, participate in this injury.

Gramicidin A aggregation in supported gel state phosphatidylcholine bilayers

Using an atomic force microscope, supported bilayers of saturated phosphatidylcholine (in the gel state) containing various amounts of gramicidin A (gA) were imaged in aqueous solutions and at room temperature. gA clusters were directly observed for the first time under these conditions. It was found that, at a lower gA concentration, gA aggregated into domains, composed of small clusters along with a considerable amount of lipids. This basic aggregation unit, most likely a hexamer, remained the same for acyl chain lengths from 14 to 18 carbons. These small clusters were observed to form elongated aggregates (line type) but never into extended pure gA domains. When gA concentrations were increased, for bilayers with 16 carbons or less, gA aggregated into larger domains but the basic unit remained separated by lipid molecules. At about 5 mol % gA, a percolation-like transition occurred at which the line type aggregates were connected to each other. However, for bilayers with more than 16 carbons, multiple lamellar structures were formed at higher gA fractions and the top layer had a ripple-like surface morphology. The molecular mechanism for the formation of these peculiar structures remains to be elucidated.

High resolution surface structure of E. coli GroES oligomer by atomic force microscopy

Using atomic force microscopy (AFM) in aqueous solution, we show that the surface structure of the oligomeric GroES can be obtained up to 10 angstroms resolution. The seven subunits of the heptamer were well resolved without image averaging. The overall dimension of the GroES heptamer was 8.4 +/- 0.4 nm in diameter and 3.0 +/- 0.3 nm high. However, the AFM images further suggest that there is a central protrusion of 0.8 +/- 0.2 nm high and 4.5 +/- 0.4 nm in diameter on one side of GroES which displays a profound seven-fold symmetry. It was found that GroEL could not bind to the adsorbed GroES in the presence of AMP-PNP and Mg2+, suggesting that the side of GroES with the central protrusion faces away from the GroEL lumen, because only one side of GroES was observed under these conditions. Based on the results from both electron and atomic force microscopy, a surface model for the GroES is proposed.

Biological atomic force microscopy: from microns to nanometers and beyond

In recent years, atomic force microscopy (AFM) has become the most rapidly developing imaging method. We summarize its recent applications in structural biology, with emphasis on high-resolution imaging, and illustrate these applications with images of cell membranes, DNA, and soluble and membrane proteins. With present technology, and at room temperature, nanometer resolution of DNA and soluble proteins is achievable, although the resolution attained on cell surfaces is more limited (10-50 nm). We suggest that high-resolution imaging of cell surfaces and very high (sub-nanometer) resolution molecular imaging requires an approach that increases specimen rigidity. Operation at cryogenic temperatures, the most promising approach, is discussed, and a cryo-AFM designed for operating at ambient pressure and liquid nitrogen temperature is described. The results include high-resolution images and evidence of increased molecular rigidity at low temperatures.

Flagellar structure and hyperthermophily: analysis of a single flagellin gene and its product in Aquifex pyrophilus

The polytrichously inserted flagella of Aquifex pyrophilus, a marine hyperthermophilic bacterium growing at 85 degrees C, were isolated and purified. Electron micrographs of the 19-nm-diameter flagellar filaments show prominent helical arrays of subunits. The primary structure of these 54-kDa flagellin monomers determining the helical shape and heat stability of filaments was of particular interest. The genomic region encoding the flagellin subunit (flaA gene) and an upstream open reading frame (orf1) were cloned and sequenced. The 1,503-bp flaA and 696-bp orf1 are preceded by separate sigma 28-like promoters and ribosome-binding motifs and succeeded by palindromic transcription terminators. Both genes are actively transcribed, but the nature and function of the orf1-encoded 231-residue polypeptide remain unknown. The deduced primary structure of the 501-amino-acid flagellin encoded by flaA consists of conserved N- and C-terminal regions and a variable 246-residue central domain. In comparison to mesophilic flagellins, the thermostable A. pyrophilus flagellin is characterized by increases in aromatic residues and prolines as well as by a 7.9% +/- 3.2% increase in all hydrophobic residues that is balanced by a respective decrease in hydrophilic residues. This composition is thought to form more compact flagellin monomers and stable interface contacts between neighboring subunits in the polymer.

[Expression of the retinoic acid nuclear receptors and retinoid X receptor gene in human breast cancer]

A number of studies have shown that retinoids can inhibit malignant cell growth including certain breast carcinoma cells. Its inhibitory effect is observed only in ER positive but not in ER negative breast cancer cells. We examined retinoic acid nuclear receptors (RARs) and retinoids X receptors (RXRs) levels in 6 breast carcinoma cell lines and 18 breast cancer biopsy specimens. We found that RAR-alpha mRNA level was significantly higher in ER positive cell lines and samples. RAR-gamma mRNA was expressed at relatively high levels in majority of tumor samples independent of the ER-status while RAR-beta mRNA was expressed at low levels. We also found high RXR-alpha mRNA levels in all of the tumor samples examined while RXR-gamma mRNA could not be detected. Our study suggests a possibility that retinoids inhibit tumor cell growth through RAR-alpha and RAR-alpha levels may serve as a potential marker to determine responsiveness of patients to retinoids therapy.

Ripple phase in asymmetric unilamellar bilayers with saturated and unsaturated phospholipids

In a solution of phosphate-buffered saline (PBS), unilamellar bilayers with saturated phosphatidylcholines in one leaflet and negatively charged, unsaturated phospholipids in the other leaflet were observed in the ripple phase at room temperature using atomic force microscopy (AFM). This is the first observation of the ripple phase in asymmetric bilayers. Sodium and phosphate, components of PBS, were found to be necessary for the formation of the ripple structure in the asymmetric bilayers composed of dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoylphosphatidylglycerol (POPG), demonstrating a dependency for specific ions for this phase. These results indicate that the two leaflets of a bilayer are closely coupled to give rise to such a long range and complicated morphology.

An improved Escherichia coli-Rhodococcus shuttle vector and plasmid transformation in Rhodococcus spp. using electroporation

The genetic studies of metabolically diverse Rhodococcus spp. have been hampered by the lack of a system of introducing exogenous DNA. The authors improved an existing Escherichia coli-Rhodococcus shuttle vector (pMVS301) by removing much of the DNA not needed for replication and adding a multicloning site. This improved vector (pBS305) is 7.9 kb in length. Its ability to transform Rhodococcus was tested using electroporation parameters optimized for introduction of pMVS301 into Rhodococcus. Transformation efficiencies as high as 10(5) cfu micrograms-1 DNA were obtained although efficiencies varied depending on the Rhodococcus strain tested. The improved vector pBS305 offers great utility for genetic studies of Rhodococcus because its small size enables movement of large inserts of DNA into Rhodococcus, it has multicloning sites, contains a highly selective thiostrepton marker, and can be replicated in both E. coli and Rhodococcus.

High-resolution atomic-force microscopy of DNA: the pitch of the double helix

Using a cationic lipid bilayer, we show that DNA can be reliably adsorbed to the bilayer surface for atomic force microscopy (AFM) in aqueous buffers at high resolution. The measured width of the dsDNA is close to 2 nm, and a periodic modulation on dsDNA is reproducibly detected by the AFM. The measured period is 3.4 +/- 0.4 nm, in excellent agreement with the known pitch of the double helix. The right-handedness of the double helix is directly discernible in high resolution AFM images. Thus, this approach can be readily applied to the study of DNA-protein interactions, as well as sequence mapping at high resolution.

Mechanism research of cryoanalgesia

The sciatic nerves of rabbits were frozen at different temperatures (-20 degrees C, -60 degrees C, -100 degrees C, -140 degrees C, and -180 degrees C). The morphology and function of the frozen nerves were examined with light microscopy (hematoxylin and eosinophilin stain and a histochemical thiocholine method) and electron microscopy. The function of the nerve after freezing was assessed using short latency somatosensory evoked potentials, sensory conduction velocity, and electromyogram at various intervals after freezing. There were no changes in morphology or function of nerves cryolesioned at -20 degrees C. The nerve fibers cryolesioned at -60 degrees C showed signs of freezing degeneration and lost their conductive function although, these nerves all recovered. Approximately half of nerve fibers cryolesioned at -100 degrees C showed Wallerian degeneration, and although the time to remyelination was delayed, nerve regeneration was still complete. At -140 degrees C and -180 degrees C the nerve fibers showed immediate necrosis, with destruction of basal membranes and proliferation of collagen fibers. The results explained the mechanism of cryoanalgesia. Our study demonstrates that cryo-temperatures lower than -140 degrees C will cause permanent alterations in nerve morphology and function, whereas warmer temperatures do not result in permanent nerve damage and are therefore not likely to provide long-term analgesia to patients.

Cryo atomic force microscopy: a new approach for biological imaging at high resolution

A low-temperature atomic force microscope (cryo-AFM), operated in liquid nitrogen vapor, has been constructed for biological applications. The system provides an adjustable imaging temperature from 77 to 220 K with atomic resolution achieved on crystalline specimens. Imaging with NaCl microcrystals demonstrates that the system is free from surface contamination. Below 100 K, several biological specimens, including immunoglobulins and DNA as well as red blood cell ghosts, were imaged at high spatial resolution. Measurements on individual macromolecules showed that the mechanical strength is significantly greater at cryogenic temperatures with an estimated Young's modulus 1000-10,000 times that of a hydrated protein at room temperature, providing a solid basis for future improvements and applications of cryo-AFM in structural biology.

Conjugation fidelity and bistability in a high-efficiency mutually pumped phase conjugator with ring channels

We describe a high-efficiency mutually pumped phase conjugator with ring channels in a bird-wing incident geometry in copper-doped potassium sodium strontium barium niobate. A transmissivity as great as 35% is measured. Optical switching is obtained. The dependence of phase-conjugation fidelity on the geometric parameters and the input-beam ratio is discussed. Some suggestions are proposed to improve the fidelity further. The response times as a function of the input-beam ratio with the input beam kept constant are measured, and the least-squares minimum is used to simulate the fitting curve equations and to explain the formation of optical switching and the reduction or improvement of image fidelity.

Atomic force microscopy of cholera toxin B-oligomers bound to bilayers of biologically relevant lipids

Cholera toxin B-oligomer was imaged by atomic force microscopy (AFM) on biologically relevant model membranes, such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine and egg yolk phosphatidylcholine at room temperature in solution at a resolution in the range of 1 to 2 nm. In addition, two-dimensional arrays were grown directly on these model membranes without any special treatment, and were also imaged by AFM. These results demonstrate the ability of AFM for imaging membrane proteins at high resolution without the need of chemical cross-linking, either within the membrane or to the substratum.

Progress in high resolution atomic force microscopy in biology

The atomic force microscope (AFM) was invented by Binnig, Quate and Gerber less than 10 years ago (Binniget al. 1986). In their first prototype, a piece of goldfoil was used as the cantilever, with a crushed diamond tip mounted at the end. On the back of the cantilever, a tunnelling junction was used to monitor the deflection of the cantilever (the gold-foil) when the specimen was scanned with the tip in contact with the surface. Thus, the surface topography of the specimen was obtained with a resolution critically dependent on the sharpness of the tip provided the deformation of the specimen was not serious. Even with such a crude set-up, they managed to obtain a lateral resolution of ˜ 30 Å and a vertical resolution of better than 1 Å on an amorphous A12O3surface. The operating principle of such an instrument is deceptively simple. However, such an arrangement was inconvenient for routine operations and unsuitable for imaging hydrated specimens, because the tunnelling junction is easily contaminated in air and works poorly in aqueous solutions (Alexanderet al. 1989). As a result, the application of this type of AFM to biological samples was rare (Engel, 1991).

The retinoblastoma susceptibility gene product represses transcription when directly bound to the promoter

Rb represses E2F-mediated transcription in part by blocking the trans-activation domain of E2F. In addition, Rb can convert an E2F binding site from a positive to a negative element. To examine the effect of a Rb-DNA-bound complex on transcription, full-length Rb was fused to the DNA binding domain of GAL4. Here, we report that GAL4-Rb can repress transcription mediated by either Sp1, AP-1, or p53, dependent upon the presence of both the GAL4 DNA binding domain and GAL4 binding sites. Moreover, GAL4-Rb inhibited the activity of the herpes simplex virus tk promoter from GAL4 binding sites located at a distance from the promoter. In contrast, GAL4-Rb was unable to repress basal transcription. Cotransfection of specific cyclins and cyclin-dependent kinases or SV40 T-antigen abolished the repressive activity of GAL4-Rb. The domains of Rb involved in mediating the repression of transcription were mapped to regions that are overlapping, but not identical, to those required for the interaction with E2F. We propose that Rb can function as a general repressor of transcription when bound to the promoter region.

The retinoblastoma-susceptibility gene product binds directly to the human TATA-binding protein-associated factor TAFII250

RB, the protein product of the retinoblastoma tumor-suppressor gene, regulates the activity of specific transcription factors. This regulation appears to be mediated either directly through interactions with specific transcription factors or through an alternative mechanism. Here we report that stimulation of Sp1-mediated transcription by RB is partially abrogated at the nonpermissive temperature in ts13 cells. These cells contain a temperature-sensitive mutation in the TATA-binding protein-associated factor TAFII250, first identified as the cell cycle regulatory protein CCG1. The stimulation of Sp1-mediated transcription by RB in ts13 cells at the nonpermissive temperature could be restored by the introduction of wild-type human TAFII250. Furthermore, we demonstrate that RB binds directly to hTAFII250 in vitro and in vivo. These results suggest that RB can confer transcriptional regulation and possibly cell cycle control and tumor suppression through an interaction with TFIID, in particular with TAFII250.

Asymmetric transmission device using Fe-doped KTa(x)Nb(1-x)O(3) crystal

A new type of asymmetric optical transmission device based on contradirectional two-wave mixing between an incident beam and its backward-scattering beams in Fe-doped KTa(x)Nb(1-x)O(3) crystal is demonstrated. The transmittance ratio of the beams propagating in opposite directions can be adjusted by a change in the angle between the incident beam and the c axis; the maximum ratio is nearly 50:1 at only one incident beam. Approximate solutions of two opposite transmittances are derived and discussed. It is possible to use this device as an optical isolator or an optical diode.

Differential regulation of E2F and Sp1-mediated transcription by G1 cyclins

Cyclins have been demonstrated to mediate phosphorylation of the retinoblastoma tumor suppressor gene product (Rb) and/or to bind directly to Rb. Since Rb is a regulator of E2F and Sp1-mediated transcription, we have examined the effect of overexpression of cyclins on transcription mediated by E2F-dependent adenovirus E2 promoter and by Sp1 in a cotransfection assay in 3T3 cells. All the G1 cyclins tested, C, D1, D2, D3 and E, as well as cyclin A were able to stimulate E2 promoter activity to various levels with D3 showing the strongest stimulation. For stimulation of the E2 promoter by cyclins A, E and D-type cyclins was dependent upon the presence of functional E2F and ATF binding sites. Cyclin C, however, was able to stimulate both E2F and ATF-dependent transcription to the same level as the wild type E2 promoter. In addition, cyclin C was able to stimulate transcription mediated by Sp1, GAL4-Sp1 and GAL4-VP16, suggesting that cyclin C affects a general pathway of transcriptional activation. In contrast, cyclin D1 was able to repress specifically Sp1-mediated transcription through an Rb-independent pathway. These results suggest that cyclins can regulate transcription mediated by specific transcription factors in both positive and negative manners. Furthermore, the results demonstrate clear functional differences between the G1 cyclins, in particular, functional differences between the related D-type cyclins.

Recent advances in biological atomic force microscopy

Recent developments in biological atomic force microscopy are reviewed. In addition to the advances in methodology, new structural information of different biological systems revealed by the atomic force microscopy is also presented. A discussion regarding the contrast, resolution and specimen deformation is provided based on a theoretical model.

A physical map of the hyperthermophilic bacterium Aquifex pyrophilus chromosome

A genomic map of the hyperthermophilic hydrogen-oxidizing bacterium Aquifex pyrophilus was established with NotI (GC/GGCCGC), SpeI (A/CTAGT), and XbaI (T/CTAGA). Linking clones and cross-hybridization of restriction fragments revealed a single circular chromosome of 1.6 Mbp. A single flagellin gene and six rRNA gene units were located on this map by Southern hybridization.

Regulation of pml messenger-RNA expression in human breast-carcinoma cells

We examined the mRNA expression profile of PML, a novel nuclear protein recently characterized from acute promyelocytic leukemia (APL) blast cells, in a number of breast carcinoma cell lines. PML mRNA was found to be differentially expressed among the cell lines examined. A correlation of borderline significance between PML mRNA expression and the proliferative capacity of the cell Lines was noted. Serum stimulation significantly elevated the PML mRNA levels in the T47D and MDA-MB-231 cells. These results would suggest that PML may function as a positive regulator of cellular proliferation in breast carcinoma cells.

Enhancement of intestinal insulin absorption by bile salt-fatty acid mixed micelles in dogs

The pharmacokinetics and pharmacodynamics of porcine zinc insulin following intravenous (iv), intrajejunal, and ileocolonic delivery were evaluated in dogs. The concentration-time profile of plasma immunoreactive insulin following iv injection could be best described by a two-compartment model with a mean distribution half-life of 1.1 min and a mean elimination half-life of 5.6 min. Maximum hypoglycemia occurred at 15 min after injection. Intrajejunal administration of 10 units/kg insulin in phosphate-buffered saline resulted in minimal insulin absorption or hypoglycemia. Incorporation of mixed micelles containing 30 mM sodium glycocholate and 40 mM linoleic acid significantly improved enteral insulin absorption. When delivered with mixed micelles, the mean absolute bioavailability of insulin was 1.8%. To study the effect of intestinal site on insulin uptake, the same formulation was delivered to the ileocolonic region. The mean absolute bioavailability of insulin absorbed from this site was 0.6%. Delivery of insulin to both sites caused significant hypoglycemia in all dogs. Insulin combined with mixed micelles is enterally absorbed in dogs; however, the bioavailability is much lower than that observed in similar studies with rats.

Alcohol induces interdigitated domains in unilamellar phosphatidylcholine bilayers

Using the atomic force microscope (AFM) in situ, we have demonstrated that acyl chain interdigitation can be induced reversibly by alcohol in supported unilamellar phospholipid bilayers. At alcohol concentrations considerably lower than the critical values determined by other experimental techniques, it was found that interdigitated domains can be induced and these domains were stable over a long period of time. The mechanism of such domain formation remains to be elucidated. This work also serves as an example to illustrate the uniqueness of the AFM as a powerful tool in the study of membrane structure and conformation under physiological conditions at high spatial resolution.

A high-sensitivity CCD system for parallel electron energy-loss spectroscopy (CCD for EELS)

A cooled frame transfer CCD camera system was developed and tested as a parallel detector in an electron energy-loss spectrometer mounted on a transmission electron microscope. The use of a shutterless camera with a frame transfer CCD collected virtually 100% of the photon signal with a reasonably fast acquisition time. The system detective quantum efficiency was over 90% under normal experimental conditions. Because of the low channel to channel gain variations in the CCD, the signal-to-noise ratio and the detection limit were substantially better than that obtained with a silicon intensified target (SIT) camera, and direct fitting to the standard data was feasible. Quantitation at the phosphorus L edge generated from a phosphoprotein, phosvitin, showed that, under identical experimental conditions, direct fitting of spectra obtained with this CCD system gave better sensitivity than that given by the SIT camera system. Because of its larger pixel charge well, the CCD system can also operate at a much higher beam current, resulting in a significant reduction in the time required for elemental mapping at a given sensitivity.

Cyclodextrins as mucosal absorption promoters of insulin. II. Effects of beta-cyclodextrin derivatives on alpha-chymotryptic degradation and enteral absorption of insulin in rats

The relative effectiveness of two beta-cyclodextrin derivatives, i.e., dimethyl-beta-cyclodextrin (DM beta CD) and hydroxypropyl-beta-cyclodextrin (HP beta CD), in enhancing enteral absorption of insulin was evaluated in the lower jejunal/upper ileal segments of the rat by means of an in situ closed loop method. The incorporation of 10% (w/v) DM beta CD to a 0.5 mg/ml porcine-zinc insulin solution dramatically increased insulin bioavailability from a negligible value (approximately 0.06%) to 5.63%, when administered enterally at a dose of 20 U/kg. However, addition of 10% (w/v) HP beta CD did not improve enteral insulin uptake significantly with a bioavailability of only 0.07%. Similarly, the pharmacodynamic relative efficacy values obtained after the enteral administration of 20 U/kg insulin, 20 U/kg insulin with 10% HP beta CD, and 20 U/kg insulin with 10% DM beta CD were 0.24%, 0.26%, and 1.75%, respectively. Biodegradation studies of 0.5 mg/ml insulin hexamers by 0.5 microM alpha-chymotrypsin revealed no inhibitory effect on the enzymatic activity by the two cyclodextrins. On the contrary, the apparent first-order rate constant increased significantly in the presence of 10% DM beta CD, suggesting insulin oligomer dissociation by DM beta CD. Histopathological examination of the rat intestine was performed to detect tissue damage following enteral administration of the beta-cyclodextrin derivatives. Light microscopic inspection indicated no observable tissue damage, thereby arguing direct membrane fluidization as the primary mechanism for enhanced insulin uptake. This study indicates the feasibility of using cyclodextrins as mucosal absorption promoters of proteins and peptide drugs.

Sequencing and characterization of the sdaC gene and identification of the sdaCB operon in Escherichia coli K12

We describe here the regulatory and coding region, and DNA sequence, for a newly recognized gene, sdaC, which codes for a hydrophobic protein with several predicted membrane-spanning domains. sdaC and sdaB form a single operon, with 57 bp between the end of sdaC and the start of sdaB. Expression of the sdaCB operon is regulated mainly by catabolite repression, but is also slightly sensitive to regulation by leucine-responsive regulatory protein. Cells carrying sdaC on a multicopy plasmid have increased L-serine transport capacity, insensitive to threonine, suggesting that sdaC might code for a recently described highly specific serine transporter [Kayahara, T., Thelen, P., Ogawa, W., Inaba, K., Tsuda, M., Goldberg, E. B. & Tsuchiya, T. (1992) J. Bacteriol. 174, 7482-7485].

Planar waveguide refractive index distribution functions determined precisely from mode indices

The inverse WKB (IWKB) approximation has been extended to derive the index distribution functions from the measured mode indices of a planar waveguide. Through the use of this technique, the forms of the index distribution functions are obtained by IWKB approximation and a criterion is used to derive the functions accurately. The results are compared to the exponential and Fermi distributions. It is shown that the index profile, surface index, and waveguide depth can be obtained more accurately than with the original IWKB approximation. Finally, the index distribution function of a c-cut proton-exchanged LiTaO(3) waveguide is given by this technique, the mode indices calculated with this function agree with the experimental results in the range of 10(-4).

Photorefractive-crystal shape-parameter influence on formation of self-pumped phase conjugation

The influence of crystal-shape parameters on formation of self-pumped phase conjugation is studied experimentally. The parallelism of two c-cut faces of a barium strontium potassium niobate crystal of cuboid shape is changed to control the internal oscillation and thus to induce or to suppress the generation of self-pumped phase conjugation.

Tris(hydroxymethyl)aminomethane (C4H11NO3) induced a ripple phase in supported unilamellar phospholipid bilayers

A commonly used buffer compound, tris(hydroxymethyl)aminomethane (C4H11NO3), was found to induce a ripple phase in supported unilamellar phospholipid bilayers at room temperature. The ripple structure showed various types of domains that could extend to several micrometers in length with many well-defined bendings of either 120 degrees or 60 degrees. Two different periodic ripples were found to coexist in 1,2-dipentadecanoyl-sn-glycero-3-phosphatidylcholine bilayers. Some intermediate states during the transition to the ripple phase were also observed.