Conformational changes due to calcium-induced calmodulin dissociation in brush border myosin I-decorated F-actin revealed by cryoelectron microscopy and image analysis

Brush border myosin I (BBMI) is a single-headed molecular motor. Its catalytic domain exhibits extensive sequence homology to the catalytic domain of myosin II, while its tail lacks the coiled-coil nature of myosin II. The BBMI tail domain contains at least three IQ motifs and binds calmodulin. Addition of calcium removes one of these calmodulin light chains, with effects on ATPase activity and motility in in vitro assays. Using the techniques of cryoelectron microscopy and helical image analysis we have calculated three-dimensional (3D) maps of BBMI-decorated actin filaments prepared in the presence and absence of calcium. The 3D maps describe a BBMI catalytic domain that is strikingly similar to the catalytic domain of myosin II subfragment 1 (S1), with the exception of a short amino-terminal region of the heavy chain, which is absent from BBMI. The tail domains of BBMI and S1 are highly divergent in structure, continuing on from their respective motor domains with very different geometries. Addition of calcium to BBMI, and the concomitant loss of a calmodulin light chain, results in an extensive reorganization of mass in the tail domain.

Two-dimensional crystallization of brush border myosin I

Brush border myosin-I (BBMI) is a single-headed unconventional myosin found in the microvilli of intestinal epithelial cells, where it links the core bundle of actin filaments to the plasma membrane. An association of BBMI with anionic phospholipids has been shown to be mediated by a carboxy-terminal domain which is rich in basic amino acids. We have exploited this natural affinity of BBMI for negatively charged lipids to form two-dimensional (2D) crystals of this protein which are suitable for structural analysis by electron crystallographic techniques. The 2D crystals which we have obtained belong to one of two space groups, p22121 or p2. We present here projection maps calculated from images of negatively stained crystals for each of these crystal types to a resolution of 20 A and show that the asymmetric unit is the same in both crystal types.

Evaluating rural Bangladeshi women's perspectives of quality in family planning services

Several frameworks for understanding the quality of family planning care have been proposed. However, efforts to measure and quantify their components remain underdeveloped, especially with regard to nonclinical care and community-based distribution. This study examines a large-scale field survey conducted among married women of reproductive age in rural Bangladesh in 1989 and 1990 to measure and evaluate rural women's perceptions of the quality of outreach services they received. Initial analysis indicates that rural women are able to distinguish between good and poor quality of care and that these perceptions can be accurately documented and quantified through sample survey approaches. Implications of the use of a survey in the measurement of quality of care are discussed, as well as implications of the results for managers within the Bangladesh government family planning program, which has been regarded by donor agencies as having limited responsiveness to clients' needs.

Lexipafant (BB-882), a platelet activating factor receptor antagonist, ameliorates mucosal inflammation in an animal model of colitis

OBJECTIVE

To assess the anti-inflammatory action of lexipafant (BB-882), a platelet activating factor antagonist, in an animal model of acute colitis.

DESIGN

An animal intervention study.

METHODS

Following the rectal instillation of formalin 0.75% into male New Zealand White (NZW) rabbits, 0.85 ml of aggregated immunoglobulin was administered i.v. Treatment groups (0.8 mg/kg, n = 6; 2.4 mg/kg, n = 13; 3.2 mg/kg, n = 10) were given bolus doses of BB-882 two-hourly i.v. (control group, n = 25). Rectal dialysis was performed before induction of colitis and sacrifice. Dialysate leukotriene B4 (LTB4), prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) levels were determined. Tissue was saved for histology and measurement of myeloperoxidase content.

RESULTS

There was a dose-dependent improvement in macroscopic scores (2.4 and 3.2 mg/kg: P < 0.02, P < 0.001) and myeloperoxidase levels (3.2 mg/kg: P < 0.04). Dialysate LTB4 levels fell (2.4 and 3.2 mg/kg: P < 0.03, P < 0.02) as did PGE2 levels. TXB2 concentrations remained unaffected.

CONCLUSION

The PAF receptor antagonist BB-882 shows efficacy in treating inflammation in an animal model of acute colitis as evidenced by a dose-dependent fall in macroscopic mucosal damage, neutrophil infiltration and reduced generation of inflammatory mediators.

Helical processing using PHOELIX

We describe here a set of procedures and algorithms for helical processing that we refer to as the PHOELIX package. The package was developed to provide a time-efficient and semiautomated method for determining a three-dimensional density map from a specimen with helical symmetry. The procedures which are part of PHOELIX are drawn from the original MRC helical processing suite with extensions principally developed using the SUPRIM image processing package. The package in its current form has been optimized for the processing of actomyosin filaments but has been modified and applied to other helical structures.

Characterisation of refractory wastes at hydrocarbon-contaminated sites-II. Screening of reference oils by stable carbon isotope fingerprinting

The preliminary evaluation of stable carbon-isotope ratio mass spectrometry (IRMS) as a novel, alternative method for screening residual heavy or weathered petroleum wastes is presented. Seven well-characterised middle-to high-boiling range oils (predominant boiling range: 150-600 degrees C) and their isolated class fractions were analysed by IRMS. Whole oil delta13C values (which express the ratio of (13)C to (12)C within each sample) showed a small but significant decrease with decreasing oil asphaltene content, from -26.8% for heavier oils to -28.8% for lighter, predominantly paraffinic oils. In agreement with the conventionally observed trend, delta13C values of isolated class fractions were found to increase in the following order: delta13Csat (congruent with delta13Coil) < delta13Caro < delta13Cpol < delta13Casp, delta13Csat up to 2.5% more negative than delta13Cpol and delta13Casp. However, this variation was much less pronounced for the heavier oil samples. As a result, isotope type curves exhibited a clear distinction between heavier oils, which produced much flatter type curves, and lighter oils, for which type curves were characteristically sloping. From these preliminary results, IRMS would appear to have application as a potential method for identifying a predominance of asphaltene class fractions in residual hydrocarbon wastes and for distinguishing between heavy and light oily contaminants.

A 35-A movement of smooth muscle myosin on ADP release

Myosin II crossbridges interact with F-actin producing powerstrokes of around 100 A (refs 1, 2), during which the products of ATP hydrolysis are released. This has been postulated to involve an articulation of the myosin head (S1) on actin, or substantial conformational changes in S1 itself. Small movements of the regulatory light chain have been detected (see, for example, refs 9, 10), but most data suggest that the bulk of S1 does not move on actin during crossbridge cycling. Here we present three-dimensional maps of S1-decorated F-actin in the presence and absence of MgADP. The myosin motor domain is similar in both states but there are major orientational differences in the light-chain-binding domain. This domain acts as a rigid level arm pivoting about the end of the motor domain and swinging approximately 23 degrees, resulting in a approximately 35-A step. Small, nucleotide-mediated conformational changes in the motor domain may thus be converted by the light-chain domain into large movement steps.

PHOELIX: a package for semi-automated helical reconstruction

We describe a set of procedures and algorithms which have been developed to provide an efficient and reliable method for reconstructing a three-dimensional density map from specimens with helical symmetry. These procedures build on the original MRC helical processing suite, with extensions principally developed using the SUPRIM image processing package. Actomyosin is used as a model specimen to demonstrate the utility of this repackaged and expanded set of routines. The time required to complete a three-dimensional map has been reduced from several weeks using traditional manual techniques to a few days. The increased signal/noise provided has allowed for the extraction of additional layer lines not previously identified by manual techniques.

Amelioration of experimental acute pancreatitis with a potent platelet-activating factor antagonist

The effect of a potent platelet-activating factor (PAF) antagonist, BB-882, on an experimental model of acute pancreatitis induced in male Wistar rats by a technique of microvascular ischaemia was studied. A single intraperitoneal injection of BB-882 (5 mg/kg) 30 min after induction of the disease in 12 animals significantly reduced (P < 0.001) the rise in the level of serum amylase (mean 2477 (range 2100-3280) units/l) compared with that in 12 control animals (mean 3928 (range 2800-5900) units/l) and significantly improved (P < 0.001) the mean pancreatic histology score (5.0 (range 3-10) versus 12.3 (range 8-18) in controls). PAF is a biologically active ether phosphorylcholine synthesized in cell membranes and a potent inflammatory mediator. Pancreatic tissue levels of this compound are increased in experimental acute pancreatitis and pretreatment with PAF receptor antagonists can ameliorate the progression of this disease. BB-882 alters the early course of experimental pancreatitis and may have a clinical therapeutic role.

Structural characterization of the copper site in galactose oxidase using X-ray absorption spectroscopy

X-ray absorption spectroscopy has been used to characterize the local structural environment of the Cu ion in the reductively inactivated, oxidatively activated, and active+substrate oxidation state derivatives of galactose oxidase. In all three cases, the local environment of the Cu is best modeled by a single shell of low-Z (N or O) scatterers. This is generally consistent with the structure determined crystallographically, although the EXAFS bond lengths are slightly, but significantly, shorter than those found crystallographically. The best-fit average bond lengths are 1.97, 1.95, and 1.98 A for inactive, active, and active+substrate, respectively. The CuII ion in the active and inactive derivatives has an apparent coordination number of 4, consistent with the equatorial ligation seen crystallographically. The CuI ion in the reduced+substrate derivative appears to have either a lower coordination number or a significantly more distorted local environment. The observed CuI-(N/O) bond length favors a model where the Cu become 3-coordinate in the substrate-reduced complex.

UnCover: the article access solution

The current climate for academic libraries is such that traditional collection development philosophies are being examined anew. The rising cost of journals, coupled with steady or declining budgets, has necessitated a review of the means for providing access to information at the local level. Where once the local collection was all-important, the focus now has shifted in other directions. As Leach describes it, libraries will begin to shift collection development funds to document delivery services. Instead of purchasing resources "just in case," the new paradigm may be purchasing information "just in time". Anticipating this shift and taking advantage of existing technologies, the UnCover Company has developed a service that, although relatively new, has been widely discussed.

A Monte Carlo pharmacophore generation procedure: application to the human PAF receptor

A novel pharmacophore definition procedure is described, which uses a Monte Carlo method to superimpose molecules. Pharmacophore space is searched by a technique similar to high temperature annealing. Subsequent refinement of candidate pharmacophores by energy minimization produces low-energy conformations that may be involved in receptor binding. The method has been applied to compounds that bind to the human platelet-activating factor (PAF) receptor. Alternative binding site models for the PAF receptor are presented and discussed.

Structure of the actin-myosin complex and its implications for muscle contraction

Muscle contraction consists of a cyclical interaction between myosin and actin driven by the concomitant hydrolysis of adenosine triphosphate (ATP). A model for the rigor complex of F actin and the myosin head was obtained by combining the molecular structures of the individual proteins with the low-resolution electron density maps of the complex derived by cryo-electron microscopy and image analysis. The spatial relation between the ATP binding pocket on myosin and the major contact area on actin suggests a working hypothesis for the crossbridge cycle that is consistent with previous independent structural and biochemical studies.

Programs for visualization in three-dimensional microscopy

Three-dimensional data representing biological structures can be derived using several methods, including serial section reconstruction, optical sectioning, and tomography. The investigation, comprehension, and communication of structural relationships to others is greatly facilitated by computer-based visualization procedures. We describe SYNU, a suite of programs developed for interactive investigation of three-dimensional structure and for the production of high-quality three-dimensional images and animations. We illustrate the capabilities of SYNU in applications to biological data obtained by confocal light microscopy, serial section, and high-resolution electron microscopy from investigations at the cellular, subcellular, and molecular levels.

Immunological assay of erythrocyte acetylcholinesterase

An immunoassay for the quantitation of erythrocyte surface acetylcholinesterase is described; using a red cell suspension, bound mouse monoclonal acetylcholinesterase antibody is detected by an alkaline phosphatase conjugated rabbit anti mouse IgG. Extraction is not required. In addition, the activity of erythrocyte surface acetylcholinesterase using dithiobisnitrobenzoate to detect released thiocholine has been measured. The coefficient of variation for each method is 7%. Reference ranges have been established for healthy adults and cord blood.

Quantification and phenotyping of serum cholinesterase by enzyme antigen immunoassay: methodological aspects and clinical applicability

An enzyme antigen immunoassay for a specific determination of serum cholinesterase is described. Polyclonal and monoclonal antibodies against cholinesterase have been used. Hydrophobic binding of the specific antibody to a microtitre plate was followed by incubation with the samples, and the activity of the bound cholinesterase was assayed by the Ellman method. The procedure has been optimized and characterized, with respect to antigen specificity, and the applicability of the assay for cholinesterase phenotyping is demonstrated. The cholinesterase activities, dibucaine-, scoline-, fluoride- and urea numbers were comparable with established reference values. The high sensitivity and specificity of the assay has been used for determination of cholinesterase in amniotic and cerebrospinal fluids, and its applicability in clinical medicine is indicated.

Futile cycling of a sulfate conjugate by isolated hepatocytes

The sulfate conjugate of the model compound 4-methylumbelliferone was taken up and hydrolyzed considerably more rapidly by isolated hepatocytes than was the glucuronide conjugate. Using intact hepatocytes or homogenates of hepatocytes, compounds were identified that either inhibited 4-methylumbelliferyl sulfate hydrolysis via arylsulfatase or impaired its uptake into cells. For example, sodium sulfate inhibited hydrolysis of 4-methylumbelliferyl sulfate by intact hepatocytes (half-maximal inhibition, 0.1 mM) but not by homogenates, suggesting a selective action on organic sulfate uptake at the plasma membrane. In contrast, cholesterol sulfate inhibited hydrolysis of 4-methylumbelliferyl sulfate by homogenates but not by hepatocytes, consistent with the hypothesis that cholesterol sulfate does not readily enter intact cells. Compounds that inhibited hydrolysis of 4-methylumbelliferyl sulfate by both isolated hepatocytes and microsomes include sodium sulfite (half-maximal inhibition, 0.1 mM), pregnenolone sulfate (half-maximal inhibition, 1 microM), and estrone sulfate (half-maximal inhibition, 10 microM). To test whether production of sulfate conjugates could be modified by agents affecting arylsulfatase in intact hepatocytes, we examined the effects of pregnenolone sulfate on the production of 4-methylumbelliferyl sulfate from 4-methylumbelliferone. Addition of pregnenolone sulfate (100 microM) to intact cells increased rates of 4-methylumbelliferone sulfate production and decreased the fraction of 4-methylumbelliferone converted into the glucuronide. Hydrolysis of 4-methylumbelliferyl sulfate by isolated microsomes was inhibited in a dose-dependent manner by adenosine 3'-phosphate 5'-phosphosulfate (PAPS) when cytosol, a source of sulfotransferase was present. Furthermore, addition of low concentrations of PAPS (0.5 microM) to a reconstituted system of microsomes and cytosol impaired the formation of fluorescent product from 4-methylumbelliferyl sulfate until PAPS was consumed, indicating that futile cycling via arylsulfatase and sulfotransferase occurred. Subsequent futile cycling of free 4-methylumbelliferone and 4-methylumbelliferyl sulfate occurred upon repeated additions of PAPS and was prevented by sodium sulfite, an inhibitor of arylsulfatase. These results argue strongly that sulfate conjugate production within hepatocytes is regulated by futile cycling via sulfotransferase and arylsulfatase. Thus, drugs and endogenous substances that affect arylsulfatase may have marked effects on sulfate conjugate production by the liver.

Immunological studies of families segregating the silent gene for plasma cholinesterase

Seven families segregating apparently silent gene homozygotes have been investigated by enzyme-linked immunosorbent assays. These families confirm not only the heterogeneity of the silent gene in the form of E1s and E1t but in 3 families there is support for the segregation of the new gene E1x.