Glomerular lysozyme binding in protein-overload proteinuria

Binding of the cationic molecule lysozyme to the glomerular basement membrane and to the glomerular epithelial cell coat was investigated in the glomerulus of normal female Wistar rats and in rats in which heavy proteinuria was induced by the daily administration of 1 g of bovine serum albumin. In normal rats the binding of lysozyme to the anionic groups in the glomerular basement membrane and the cell coat had no effect on the ultrastructure of the glomerular epithelial cell, in particular the foot processes were unchanged. In the proteinuric rats the lysozyme-binding to the glomerular basement membrane and the epithelial cell coat was completely lost in the damaged glomeruli. In the apparently normal glomeruli present in these proteinuric animals binding was similar to that seen in normal rats. These results suggest that in protein-overload proteinuria there is a loss of glomerular anion and hence a reduction in the glomerular charge barrier. This may account, at least in part, for the increased glomerular leak of negatively charged serum albumin in this experimental model of proteinuria.     

The Effect of Histones and Other Basic Macromolecules on Cell Permeability and Elongation of Barley Roots

Low exogenous concentrations of calf-thymus histone, poly-l -lysine and lysozyme inhibit root elongation. These basic macromolecules (polycations) also affect cell permeability resulting in a leakage of ultraviolet light (UV)-absorbing materials and chloride ion from cells. Adenosine 5′-monophosphate was identified as one of the UV-absorbing compounds in the root exudate, by thin layer chromatography. These deleterious effects of polycations on root growth and permeability are reduced in the presence of calcium and other divalent cations. Calcium ion-histone interaction appears to exhibit competitive kinetics and suggests that both calcium and histone compete for attachment to negative sites on cell membrances.     

Mechanism of enhancement of microbial cell hydrophobicity by cationic polymers.

Polycationic polymers have been noted for their effects in promoting cell adhesion to various surfaces, but previous studies have failed to describe a mechanism dealing with this type of adhesion. In the present study, three polycationic polymers (chitosan, poly-L-lysine, and lysozyme) were tested for their effects on microbial hydrophobicity, as determined by adhesion to hydrocarbon and polystyrene. Test strains (Escherichia coli, Candida albicans, and a nonhydrophobic mutant, MR-481, derived from Acinetobacter calcoaceticus RAG-1) were vortexed with hexadecane in the presence of the various polycations, and the extent of adhesion was measured turbidimetrically. Adhesion of all three test strains rose from near zero values to over 90% in the presence of low concentrations of chitosan (125 to 250 micrograms/ml). Adhesion occurred by adsorption of chitosan directly to the cell surface, since E. coli cells preincubated in the presence of the polymer were highly adherent, whereas hexadecane droplets pretreated with chitosan were subsequently unable to bind untreated cells. Inorganic cations (Na+, Mg2+) inhibited the chitosan-mediated adhesion of E. coli to hexadecane, presumably by interfering with the electrostatic interactions responsible for adsorption of the polymer to the bacterial surface. Chitosan similarly promoted E. coli adhesion to polystyrene at concentrations slightly higher than those which mediated adhesion to hexadecane. Poly-L-lysine also promoted microbial adhesion to hexadecane, although at concentrations somewhat higher than those observed for chitosan. In order to study the effect of the cationic protein lysozyme, adhesion was studied at 0 degree C (to prevent enzymatic activity), using n-octane as the test hydrocarbon. Adhesion of E. coli increased by 70% in the presence of 80 micrograms of lysozyme per ml. When the negatively charged carboxylate residues on the E. coli cell surface were substituted for positively charged ammonium groups, the resulting cells became highly hydrophobic, even in the absence of polycations. The observed "hydrophobicity" of the microbial cells in the presence of polycations is thus probably due to a loss of surface electronegativity. The data suggest that enhancement of hydrophobicity by polycationic polymers is a general phenomenon.     

Interaction of bacterial lipopolysaccharides with host soluble proteins and polycations

Lipopolysaccharides (LPS) are unique cell wall components of gram-negative bacteria. They represent amphiphilic biopolymeric compounds combining in a single molecule hydrophilic (O-specific chains, core oligosaccharide, etc.) and hydrophobic (lipid A) entities. LPS play a crucial role in various interactions between micro- and macroorganisms and display a broad range of biological activities including toxic activity and ability to activate immune cells. Biological activities of LPS are based on their ability to bind with high affinity to mammalian proteins, e.g., lipoproteins, bactericidal permeability-increasing proteins, lysozyme, etc., and thus to neutralize toxic effects of endotoxins. LPS are specific targets for antimicrobial polycationic compounds used in the therapy of bacterial infections. Studies of mechanisms of toxic effects of LPS culminated in the development of novel approaches to LPS neutralization. One of them is based on the use of compounds able to neutralize LPS toxicity at the expense of formation of macromolecular complexes with them. This approach is highly specific and has no effect on functional activity of antipathogenic defense mechanisms of the host. Interaction of LPS with various classes of cationic amphiphilic molecules including proteins, peptides, and polyamines was the subject of intensive studies in the past decade. Binding of cationic polymers is provided by electrostatic interactions between LPS and negatively charged phosphate and carboxylic groups of LPS localized in lipid A core. The present study is an overview of recently published data on different mechanisms of interactions of LPS with soluble proteins and polycations and modification of physiological activity of LPS.     

The cytochrome P-450cam binding surface as defined by site-directed mutagenesis and electrostatic modeling

Cytochrome P-450cam cationic surface charges at Lys 344, Arg 72, and Lys 392 have been altered by site-directed mutagenesis techniques. The residues at Lys 344 and Arg 72 were previously suggested as salt bridge contacts in the cytochrome b5-cytochrome P-450cam association complex and implicated in the physiological putidaredoxin-cytochrome P-450cam complex [Stayton, P. S., Poulos, T. L., & Sligar, S. G. (1989) Biochemistry 28, 8201-8205]. Mutations to neutralize the basic charge at Arg 72 (R72Q) and to both neutralize and reverse the charge at Lys 344 (K344Q, K344E) resulted in alteration of NADH oxidation rates in the reconstituted physiological electron-transfer system, which is rate limited by putidaredoxin-cytochrome P-450cam electron transfer. The steady-state Vmax values were apparently unperturbed, suggesting that the observed rate differences were largely attributable to Km effects. The Km values observed for the K344Q (24 microM) and K344E (32 microM) mutants are in the direction expected for neutralization and reversal of a salt bridge charge interaction. A control mutation at a basic surface charge located away from the proposed site of interaction, Lys 392 (K392Q), resulted in overall activities quantitated by NADH oxidation rates that are similar to that of wild-type cytochrome P-450cam. Calculation of the cytochrome P-450cam electrostatic field revealed a patch of positive potential at the modeled cytochrome b5 interaction site lying directly above the nearest proximal approach to the buried heme prosthetic group. These results provide experimental and theoretical evidence for the modeled cytochrome P-450cam binding site implicated in both cytochrome b5 and putidaredoxin association.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enzymatic Activity of Cytochrome C-Oxidase Inserted into Magnetoliposomes Differing in Surface Charge Density

The role played by the surface charge density of the phospholipid coat of nanometer-sized Fe₃O₄ colloids (so-called “magnetoliposomes”) in the catalytic activity of beef heart cytochrome c oxidase was investigated. Screening of various binary mixtures of the anionic dimyristoylphosphatidylglycerol and the zwitterionic dimyristoylphosphatidylcholine demonstrated that the highest degree of reactivation was found in the lower negative charge range. Pre-incubation of the charged colloidal biocatalytic particles with cytochrome c induced aggregation and reduced overall enzymatic activity. The results are interpreted in terms of a different affinity of the substrate for the various membrane types and of a reorganisation of the enzyme within the membrane matrices.     

Simultaneous measurements of optical and electrical properties of artificial membranes composed of mitochondrial lipids and their interaction with cytochrome c.

A newly constructed cell, which allows simultaneous measurements of optical and electrical properties, was used to study bimolecular black membranes composed of beef heart mitochondrial lipids and their interaction with cytochrome c. The results show that these highly charged membranes are stable only in relatively limited ranges of boundary conditions. In 0.1 n KCl their maximum direct current (dc) resistance is 7 X 10(8) Ohm cm2 +/- 10%; the series capacity at 1 kHz is 0.43 muF/cm2 +/- 3%; the entire thickness, determined by optical reflectivity, is 5.8 +/- 0.2 nm. The interaction between oxidized cytochrome c and these lipid membranes is primarily of electrostatic nature, and dependent on the presence of highly charged phospholipids, such as diphosphatidyl glycerol (cardiolipin) and phosphatidyl ethanolamine. The attachment of cytochrome c maximally causes a 2.5-fold increase in reflectivity, without any noticeable change in the capacity. This leads to a subsequent instability of the membrane (i.e., rupture) preceded by a rapid increase of the dc conductivity. This behavior is far less pronounced with reduced cytochrome c.     

Glycosaminoglycan sulfation requirements for respiratory syncytial virus infection

Glycosaminoglycans (GAGs) on the surface of cultured cells are important in the first step of efficient respiratory syncytial virus (RSV) infection. We evaluated the importance of sulfation, the major biosynthetic modification of GAGs, using an improved recombinant green fluorescent protein-expressing RSV (rgRSV) to assay infection. Pretreatment of HEp-2 cells with 50 mM sodium chlorate, a selective inhibitor of sulfation, for 48 h prior to inoculation reduced the efficiency of rgRSV infection to 40%. Infection of a CHO mutant cell line deficient in N-sulfation was three times less efficient than infection of the parental CHO cell line, indicating that N-sulfation is important. In contrast, infection of a cell line deficient in 2-O-sulfation was as efficient as infection of the parental cell line, indicating that 2-O-sulfation is not required for RSV infection. Incubating RSV with the purified soluble heparin, the prototype GAG, before inoculation had previously been shown to neutralize its infectivity. Here we tested chemically modified heparin chains that lack their N-, C6-O-, or C2-O-sulfate groups. Only heparin chains lacking the N-sulfate group lost the ability to neutralize infection, confirming that N-sulfation, but not C6-O- or C2-O-sulfation, is important for RSV infection. Analysis of heparin fragments identified the 10-saccharide chain as the minimum size that can neutralize RSV infectivity. Taken together, these results show that, while sulfate modification is important for the ability of GAGs to mediate RSV infection, only certain sulfate groups are required. This specificity indicates that the role of cell surface GAGs in RSV infection is not based on a simple charge interaction between the virus and sulfate groups but instead involves a specific GAG structural configuration that includes N-sulfate and a minimum of 10 saccharide subunits. These elements, in addition to iduronic acid demonstrated previously (L. K. Hallak, P. L. Collins, W. Knudson, and M. E. Peeples, Virology 271:264-275, 2000), partially define cell surface molecules important for RSV infection of cultured cells.     

Inability of mesoderm cells to locomote on the modified free surface of epithelial cell sheets in vitro

Summary Previous work has shown that when chick embryo mesoderm tissue is seeded onto the free, dorsal surface of established sheets of embryonic epithelial endoblast, the former penetrates the latter and spreads on the underlying artificial substratum. In this work, the surface charge on the epithelial sheet has been altered, prior to seeding the mesoderm, to ascertain whether such a change could alter the behavior of the mesoderm with respect to the free surface of the epithelium. Charge alteration was accomplished using the polycations, poly-l-lysine and dilysine. Surface charge characteristics were examined ultrastructurally using cationized and anionized ferritin. Results showed that although surface charge changes were detectable, there was no difference in the behavior of the mesoderm with respect to the endoblast. Neuraminidase did not detectably affect the epithelial surface charge. These results are consistent with the view that changes in substratum surface charge are not necessarily correlated with changes in adhesiveness.     

Investigating protein-protein interaction surfaces using a reduced stereochemical and electrostatic model

A method of calculating the electrostatic potential energy between two molecules, using finite difference potential, is presented. A reduced charge set is used so that the interaction energy can be calculated as the two static molecules explore their full six-dimensional configurational space. The energies are contoured over surfaces fixed to each molecule with an interactive computer graphics program. For two crystal structures (trypsin-trypsin inhibitor and anti-lysozyme Fab-lysozyme), it is found that the complex corresponds to highly favourable interacting regions in the contour plots. These matches arise from a small number of protruding basic residues interacting with enhanced negative potential in each case. The redox pair cytochrome c peroxidase-cytochrome c exhibits an extensive favourably interacting surface within which a possible electron transfer complex may be defined by an increased electrostatic complementarity, but a decreased electrostatic energy. A possible substrate transfer configuration for the glycolytic enzyme pair glyceraldehyde phosphate dehydrogenase-phosphoglycerate kinase is presented.     

The structure of ferrocytochrome b5 at 2.8 A resolution.

Crystals of cytochrome b5 reduced by sodium dithionite are isomorphous with the oxidized form. An electron density difference map between the two forms was calculated at 2.8 A resolution. There are no changes in main chain conformation or internal side chain orientation upon reduction. However, an ion becomes attached at the entrance of the heme crevice causing displacement of a surface lysine side chain on an adjacent molecule. The ion, identified as a cation by the nature of its coordinating ligands, appears to neutralize one of the heme propionate groups which is partially buried. It is proposed that the negatively charged propionate serves to neutralize the net formal positive charge on the heme iron in the oxidized cytochrome and that the neutralization of the heme iron upon reduction then leads to binding of a cation to the propionate.     

An Analysis of the Interaction of Sodium Dodecyl Sulfate with Lysozyme

The interaction of SDS with lysozyme was analyzed with enzyme activity and with NMR, fluorescence, and UV difference spectroscopies using various alkyl sulfates and variously modified lysozymes. SDS formed a stable complex with lysozyme without causing a gross conformational change in the enzyme molecule. Some SDS molecules bound to the active site cleft of lysozyme and therefore strongly inhibited the activity of lysozyme. Hydrophobic regions and positive charges for protein side, and a hydrophobic tail (possibly more than 8 carbons in alkyl chain) and a negative charge for detergent side were required for the formation of the complex.     

Mechanistic insights into protein precipitation by alcohol

Ethanol is used to precipitate proteins during various processes, including purification and crystallization. To elucidate the mechanism of protein precipitation by alcohol, we have investigated the solubility and structural changes of protein over a wide range of alcohol concentrations. Conformation of hen egg-white lysozyme was changed from native to α-helical rich structure in the presence of ethanol at concentrations above 60%. The solubility of lysozyme was reduced with increasing ethanol concentration, although gel formation at ethanol concentrations between 60% and 75% prevented accurate solubility measurements. SH-modified lysozyme showed largely unfolded structure in water and α-helical structure in the presence of ethanol. More importantly, solubility of the chemically modified lysozyme molecules decreased with increasing ethanol concentration. There is no indication of increased solubility upon unfolding of the lysozyme molecules by ethanol, indicating that any favorable interaction of ethanol with the hydrophobic side chains, if indeed occuring, is offset by the unfavorable interaction of ethanol with the hydrophilic side chains and peptide bonds.     

The surface charge of human glutaraldehyde-fixed erythrocytes

We measured the number of charged residues at the surface of fresh human erythrocytes after fixation with glutaraldehyde by polyelectrolyte titration using polycations of different chemical composition and various molecular weights. Independent of the reagents used, the number was (8.5 +/- 1.5) X 10(8) negatively charged residues per cell. The surface charge density of 6.3 e/nm2 is considerably higher than that calculated from the electrophoretic mobility for which the surface charge density is calculated to be 0.09 e/nm2.     

Structure of the soluble domain of cytochrome c(552) from Paracoccus denitrificans in the oxidized and reduced states

The crystal structure of the soluble domain of the membrane bound cytochrome c(552) (cytochrome c(552)') from Paracoccus denitrificans was determined using the multiwavelength anomalous diffraction technique and refined at 1.5 A resolution for the oxidized and at 1. 4 A for the reduced state. This is the first high-resolution crystal structure of a cytochrome c at low ionic strength in both redox states. The atomic model allowed for a detailed assessment of the structural properties including the secondary structure, the heme geometry and interactions, and the redox-coupled structural changes. In general, the structure has the same features as that of known eukaryotic cytochromes c. However, the surface properties are very different. Cytochrome c(552)' has a large strongly negatively charged surface part and a smaller positively charged area around the solvent-exposed heme atoms. One of the internal water molecules conserved in all structures of eukaryotic cytochromes c is also present in this bacterial cytochrome c. It contributes to the interactions between the side-chain of Arg36 and the heme propionate connected to pyrrole ring A. Reduction of the oxidized crystals does not influence the conformation of cytochrome c(552)' in contrast to eukaryotic cytochromes c. The oxidized cytochrome c(552)', especially the region of amino acid residues 40 to 56, appears to be more flexible than the reduced one.     

Effect of different drugs on a cytochrome c--phospholipid bilayer membrane.

Liposomes were prepared from dipalmitoyl phosphatidylcholine and dicetylphosphate and their interaction with the extrinsic membrane protein cytochrome c examined in terms of changes in 22Na permeability, electrophoretic mobility, protein binding, and motion of an incorporated spin label. The amount of cytochrome c bound displays no significant temperature dependence over the temperature range studied (from 30 to 55 degrees C) whereas cytochrome c causes an increase in 22Na efflux only above the phospholipid phase transition temperature. Interaction of the protein with the lipid vesicles causes no significant disturbance in the bilayer interior as monitored by the motion of the incorporated spin probe. The drugs 2,4-dinitrophenol and ethacrynic acid, both of which increase the magnitude of the vesicle negative charge, enhance both cytochrome c binding and its effect on 22Na permeability. In contrast, the local anesthetic dibucaine, which induces a positive surface charge on these liposomes, reduces both protein binding and the protein-induced increase in 22Na efflux. Finally, the chemicals butylated hydroxytoluene, 2-tert-butylphenol, and tert-butylbenzene, all of which cause early 'melting' of the phospholipid fatty acyl chains, block the capacity of cytochrome c to enhance 22Na permeability while having no effect on its binding to the vesicles.     

Enzymatic Activity of Cytochrome C-Oxidase Inserted into Magnetoliposomes Differing in Surface Charge Density

The role played by the surface charge density of the phospholipid coat of nanometer-sized Fe₃O₄ colloids (so-called “magnetoliposomes”) in the catalytic activity of beef heart cytochrome c oxidase was investigated. Screening of various binary mixtures of the anionic dimyristoylphosphatidylglycerol and the zwitterionic dimyristoylphosphatidylcholine demonstrated that the highest degree of reactivation was found in the lower negative charge range. Pre-incubation of the charged colloidal biocatalytic particles with cytochrome c induced aggregation and reduced overall enzymatic activity. The results are interpreted in terms of a different affinity of the substrate for the various membrane types and of a reorganisation of the enzyme within the membrane matrices.     

Phosphorylation of rat brain mitochondrial voltage-dependent anion as a potential tool to control leakage of cytochrome c

Apoptosis is a controlled form of cell death that participates in development, elimination of damaged cells and maintenance of cell homeostasis. Also, it plays a role in neurodegenerative disorders like Alzheimer's disease. Recently, mitochondria have emerged as being pivotal in controlling apoptosis. They house a number of apoptogenic molecules, such as cytochrome c, which are released into the cytoplasm at the onset of apoptosis. When rat brain mitochondrial voltage-dependent anion channel (VDAC), an outer mitochondrial membrane protein, interacts with Bcl-2 family proteins Bax and tBid, its pore size increases, leading to the release of cytochrome c and other apoptogenic molecules into the cytosol and causing cell death. Regulation of this tBid- and Bax-induced increase in pore size of VDAC is a significant step to control cell death induced by cytochrome c. In this work, we have shown, through bilayer electrophysiological experiments, that the increase in VDAC conductance as a result of its interaction with Bax and tBid is reduced because of the action of cyclic AMP-dependent protein kinase A (PKA) in the presence of ATP. This indicates that the increase in the pore size of VDAC after its interaction with Bax and tBid is controlled via phosphorylation of this channel by PKA. This, we believe, could be a mechanism of controlling cytochrome c-mediated cell death in living cells.     

NAD-sensitive hydrogel for the release of macromolecules

A hydrogel membrane containing immobilized ligands and receptors was synthesized and investigated for the controlled diffusion of test proteins (cytochrome C and hemoglobin). Both Cibacron blue (ligand) and lysozyme (receptor) were covalently linked to dextran molecules that were subsequently crosslinked to form a gel. The resulting stable hydrogels contained both covalent and affinity crosslinks such that their intrinsic porosities were sensitive to competitive displacers of the affinity interaction between lysozyme and Cibacron blue. Transport experiments in a twin chamber diffusion cell showed that as NAD was added to the donor side, the dissociation of the binding sites between the Cibacron blue and the lysozyme led to an increase in protein diffusion through the hydrogel. The results showed that addition of NAD caused a saturable concentration-dependent increase in the transport of both cytochrome C and hemoglobin. This effect was shown to be both specific and reversible.