Model for Stress-induced Protein Degradation in Lemna minor

Transfer of Lemna minor fronds to adverse or stress conditions produces a large increase in the rate of protein degradation. Cycloheximide partially inhibits stress-induced protein degradation and also partially inhibits the protein degradation which occurs in the absence of stress. The increased protein degradation does not appear to be due to an increase in activity of soluble proteolytic enzymes. Biochemical evidence indicates that stress, perhaps acting via hormones, affects the permeability of certain membranes, particularly the tonoplast. A general model for stress-induced protein degradation is presented in which changes in membrane properties allow vacuolar proteolytic enzymes increased access to cytoplasmic proteins.

The mechanism of deuterium oxide-induced protein degradation in Lemna minor

Transfer of Lemna minor fronds to culture medium containing 50% (v/v) deuterium oxide induces a large increase in the rate of protein breakdown, which is not due to an increase in the activity of acidic or neutral proteolytic enzymes or peptidases. Biochemical and ultrastructural evidence indicates that deuterium oxide affects the properties of certain membranes, particularly the tonoplast, and allows vacuolar proteolytic enzymes to pass into the cytoplasm and cause the increased protein breakdown.

Hydroxyproline: its asymmetric distribution in a cell wall glycoprotein

The main structural glycoprotein of the cell wall of Chlamydomonas reinhardii has been cleaved by thermolysin into glycopeptides which have been separated into three fractions, T1, T2 and T3. These correspond to three distinct domains within the glycoprotein, characterized by the asymmetric distribution of both sugars and amino acids, in particular hydroxyproline. T2 is very rich in hydroxyproline (43 mol %) and is highly glycosylated, while T3 is poor in hydroxyproline and contains very little carbohydrate. The results are discussed in terms of cell wall glycoproteins and their function.

Glycoprotein conformation in plant cell walls : Circular dichroism reveals a polyproline II structure

The major structural glycoprotein of the cell wall of Chlamydomonas reinhardii has a protein core, at least 50% of which is in the unusual polyproline II conformation. This has been demonstrated by examining the circular dichroism of the cell wall, its constituent glycoproteins, and thermolysin released wall glycopeptides. One of these glycopeptides, T2, has a high hydroxyproline and sugar content, and possesses upward of 85% polyproline II structure. The main extracellular matrix glycoprotein therefore has a rigid, rod-like structure and the significance of this and its relation to higher plant cell wall glycoproteins is discussed. The unusual conformation appears to confer great stability on the glycoprotein as it is unchanged either by certain denaturing agents or during the transition from protomer to assembled cell wall.

Cell wall glycoproteins from Chlamydomonas reinhardii, and their self-assembly

We have investigated the in vitro reassembly of the salt soluble, hydroxyproline rich, glycoproteins from the cell wall of Chlamydomonas reinhardii, into structured cell wall fragments. We have devised an assay which has been used to follow the reassembly of the unfractionated and fractionated (2BI and 2BII) cell wall glycoproteins. Reassembly has a pH optimum of 5, a temperature optimum of 20°C, and the final size of the reassembled fragments appears to be promoted by the minor component 2BI. Periodate oxidation experiments show that sugar residues, in particular mannose, are important for accurate reassembly. Using electron microscopy, the structure of the reassembled products has been elucidated, as have intermediate stages in the reassembly process.

Physical environment and job satisfaction in a community mental health center

Relocation of professional staff in a community mental health center provided a setting in which to evaluate the effects of physical environment on job satisfaction. Two mental health teams moved from an old, drab central clinic building to new satellite clinics while a third team remained in the old building. Relocated staff reported significant increase in satisfaction with physical surroundings as compared to staff that did not move. Furthermore, satisfaction with physical surroundings had some impact on overall satisfaction ratings. Physical surroundings in a community mental health center may be a mediating variable for staff morale and effectiveness.

The crystalline glycoprotein cell wall of the green alga Chlorogonium elongatum: a structural analysis

Members of the Chlamydomonaceae, mostly single-celled green algae, have been shown to contain a crystalline glycoprotein cell wall component. Most of the species examined fall into a class of algae whose walls have an identical crystalline unit cell. Chlorogonium elongatum has been chosen as a representative of this class in order to investigate in more detail its cell wall structure. The alga has a spindleshaped cell wall which retains its asymmetric shape on isolation. Sections from walls fized in the presence of tannic acid clearly reveal a regular subunit monolayer, about 20 nm thick, within the wall. Sodium dodecylsulphate (SDS) polyacrylamide gel electrophoresis shows the presence of at least 2 major glycoprotein species in the wall. Negatively stained purified cell walls demonstrate the crystalline nature of the cell wall. Optical diffraction of bright-field images and direct electron diffraction both give clear diffraction patterns whose spacings extend out to 3 nm and fall on a reciprocal lattice whose vectors describe a 2-dimensional unit cell within the wall 21.5 nm X 7.0 nm and an included angle of 80 degrees. Lattice defects within the cell wall are revealed by both negative staining and surface replication. Through-focal series were used to choose images with the optimal degree of underfocus for image processing. Linear integration and optical filtering of such images gave essentially the same result. A similar image was also obtained by computing the autocorrelation function of the amplitudes in the electron-diffraction pattern and the optical-diffraction pattern of the in-focus image. On the basis of these data a 2-dimensional model of the crystalline cell wall layer is presented.

A structural glycoprotein, containing hydroxyproline, isolated from the cell wall of Chlamydomonas reinhardii

A soluble extract from purified cell walls of C. reinhardii has been separated by gel filtration into three fractions which together account for 94% of the cell wall. The major fraction (accounting for 70% of the extract) is a glycoprotein, with a molecular wt. in sodium perchlorate of 298,000, which can be split into 4 electrophoretically distinct species. It contains 35% protein with high levels of hydroxyproline, arabinose and galactose, and is capable of self assembly into crystalline structures identical to those found within the cell wall. The second fraction (25% of the extract) is a similar glycoprotein, but contains 24% protein, a higher proportion of mannose, and is incapable of self assembly. The third fraction (3-6% of the extract) is shown to be an adsorbed impurity from the growth medium used.

Red cell surface structure. Stabilization by cholesterol sulfate as evidenced by scanning electron microscopy

Scanning electron microscopic studies demonstrate that the normal biconcave shape of the human erythrocyte is maintained in hypotonic saline when physiological levels (10 minus 5M) of cholesterol sulfate are added to the solutions. Cholesterol sulfate is a naturally occurring sterol conjugate in plasma and erythrocyte membranes and we propose that it may belong to that class of amphipathic molecules responsible for the maintenance of structure of the erythrocyte by interaction with membrane components.

Crystalline glycoprotein cell walls of algae: their stucture, composition and assembly

Cell walls from various algae within the Chlamydomonaceae display, when negatively stained and examined in the electron microscope, a crystalline lattice component. On the basis of the Fourier transforms of micrographs of the cell wall, the algae have been classified into five classes. Most of the algae examined fall into class II. The two-dimensional repeating morphological unit cell of the wall of each class is described and in each case is a parallelogram whose overall dimensions are all of the same order of magnitude. The implications of the classification for classical taxonomy are discussed. More detailed structural information, to a resolution of about 2.5 nm (based on optical filtering and image enhancement techniques), is presented for two of the cell wall classes. From the evidence of polyacrylamide gel electrophoresis, the cell wall of these algae is constructed primarily from a small number of high molecular mass glycoprotein species. In Chlamydomonas reinhardi it has been shown that the hydroxyproline residues in the wall glycoprotein are cross-linked to short oligosaccharides. Some of the conditions necessary for the complete in vitro reassembly of the cell wall of C. reinhardi are presented and include the presence of a discrete nucleating agent and the presence of a physical surface. Dislocations within the crystalline lattice of the cell walls are described and their role as growth points discussed.