Optically detected magnetic resonance studies of porcine pancreatic phospholipase A2 binding to a negatively charged substrate analogue

The direct binding of porcine pancreatic phospholipase A2 and its zymogen to 1,2-bis(heptanylcarbamoyl)-rac-glycerol 3-sulfate was studied by optical detection of triplet-state magnetic resonance spectroscopy in zero applied magnetic field. The zero-field splittings of the single Trp3 residue undergo significant changes upon binding of phospholipase A2 to lipid. Shifts in zero-field splittings, characterized mainly by a reduction of the E parameter from 1.215 to 1.144 GHz, point to large changes in the Trp3 local environment which accompany the complexing of phospholipase A2 with lipid. This may be attributed to Stark effects caused by the binding of a charged group near Trp3 in the enzyme-lipid complex. The cofactor, Ca2+, which is strongly bound to the enzyme active site, has an influence on the bonding, as reflected by smaller zero-field splitting shifts. A relatively small change in the Trp environment was observed for the interaction of the zymogen with lipid.     

Structural analysis of covalently labeled estrogen receptors by limited proteolysis and monoclonal antibody reactivity

We have used limited proteolysis of affinity-labeled estrogen receptors (ER), coupled with antireceptor antibody immunoreactivity, to assess structural features of ER and the relatedness of ER from MCF-7 human breast cancer and rat uterine cells. MCF-7 ER preparations covalently labeled with [3H]tamoxifen aziridine [( 3H]TAZ) were treated with trypsin (T), alpha-chymotrypsin (C), or Staphylococcus aureus V8 protease prior to electrophoresis on sodium dodecyl sulfate gels. Fluorography revealed a distinctive ladder of ER fragments containing TAZ for each protease generated from the Mr 66,000 ER: for T, fragments of 50K, 38K, 36K, 31K, 29K, and 28K that with longer exposure generated a 6K fragment; for C, fragments of 50K, 38K, 35K, 33K, 31K, 19K, and 18K that with longer exposure generated 14K and 6K fragments; and for V8, ca. 10 fragments between 62K and 28K. Two-dimensional gels revealed charge heterogeneity (two to three spots between pI 5.5 and 6.2) of the 66K ER and the T-generated 28K meroreceptor form. Immunoblot detection with the primate-specific antibody D75P3 gamma revealed that all immunoreactive fragments corresponded to TAZ-labeled fragments but that some small TAZ-labeled fragments (V8-generated forms less than 47K and T-generated forms less than 31K) were no longer immunoreactive. In contrast, use of the antibody H222Sp gamma revealed a correspondence between TAZ-labeled and immunoreactive fragments down to the smallest fragments generated, ca. 6K for T and C and 28K for V8. MCF-7 nuclear and cytosol ER showed very similar digest patterns, and there was a remarkable similarity in the TAZ-labeled and H222-immunoreactive fragments generated by proteolysis of both MCF-7 and rat uterine ER. These findings reveal great structural similarities between the human (breast cancer) and rat (uterine) ER and between nuclear and cytosol ER, indicate charge heterogeneity of ER, and allow a comparison of the immunoreactive and hormone attachment site domains of the ER. The observation that T and C generate a ca. 6K TAZ-labeled fragment that is also detectable with the H222 antibody should be of interest in studies determining the hormone binding domain of the ER and in amino acid sequencing of this region.     

Concerning the structure of photobilirubin II.

Evidence is presented which supports the postulate that the photobilirubins IIA and IIB are diastereoisomers in which the C-3 vinyl group has cyclized intramolecularly. The evidence comes principally from proton n.m.r. spectroscopy at 400 MHz and from chemical considerations. The cyclic structures require the E-configuration at the C-4 double bond in the precursor; this is the first structural evidence for the Z leads to E isomerization in bilirubin and supports the view that the precursor (photobilirubin IA or IB) is (4E, 15Z)-bilirubin. Brief irradiation of photobilirubin II gives bilirubin, a new compound (photobilirubin III) and unchanged starting material. The various photoisomers are discussed in terms of their inter-relationships and biological fates.     

Characteristics of the maintenance of the upright posture in subjects touching an external object while standing on a moving or immobile platform

Postural sway was compared for humans touching an external object while standing on an immobile or slowly moving posturographic platform. When the platform moves, the central nervous system may interpret the movement of the point of the contact with the external object as the movement of the body relative to the support or as the movement of the support itself. Thus, the information concerning the body position that is provided by the touch becomes ambiguous. It was demonstrated that contact with an external object during standing on an unstable support leads to a decrease in support sway. When a subject stands on a moving platform, this decrease is smaller than in the case of an immobile platform. Contact with an external object causes a decrease in postural responses to shank muscle vibrations on an immobile platform. On a moving platform, this decrease is nonsignificant. The change in postural sway depending on the unambiguity of afferent information is discussed in terms of the interaction between afferent signals of different modalities on the basis of the body scheme in subjects maintaining balance.Translated from Fiziologiya Cheloveka, Vol. 31, No. 1, 2005, pp. 59–65.Original Russian Text Copyright © 2005 by Kazennikov, Shlykov, Levik.     

Human skin chymotrypsin-like proteinase chymase. Subcellular localization to mast cell granules and interaction with heparin and other glycosaminoglycans

The subcellular localization of human skin chymase to mast cell granules was established by immunoelectron microscopy, and binding of chymase to the area of the dermo-epidermal junction, a basement membrane, was demonstrated immunocytochemically in cryosections incubated with purified proteinase prior to immunolabeling. Because heparin and heparan sulfate proteoglycans are major constituents of mast cell granules and basement membranes, respectively, the ability of chymase to bind to glycosaminoglycans (GAG) was investigated. Among a variety of GAGs, only binding of chymase to heparin and heparan sulfate appears physiologically significant. Binding was ionic strength-dependent, involved amino groups on the proteinase, and correlated with increasing GAG sulfate content, indicating a predominantly electrostatic association. Interaction with heparin was observed in solutions containing up to 0.5 M NaCl, and interaction with heparan sulfate was observed in solutions containing up to 0.3 M NaCl. Binding of heparin did not detectably affect catalysis of peptide substrates, but may reduce accessibility of proteinase to protein substrates. Measurements among a series of serine class proteinases indicated that heparin binding was a more common property of mast cell proteinases than proteinases stored in other secretory granules. Binding of chymase to heparin is likely to have a storage as well as a structural role within the mast cell granule, whereas binding of chymase to heparan sulfate may have physiological significance after degranulation.     

Delayed hypersensitivity and nonspecific cellular immunity. The cytotoxic activity of macrophages, natural and antibody-dependent killer cells

The experiment on (BALB/cXC57BL)F1 mice, showing a high level of delayed hypersensitivity (DH) when sensitized with BCG vaccine and Staphylococcus aureus strain B-243, has demonstrated the influence of such sensitization and DH reaction induced by the injection of a specific antigen (old tuberculin or staphylococcal phagolysate) into the sensitized animals on the cytotoxicity of macrophages, natural killers (NK) and antibody-dependent killers (ADK). Sensitization with BCG vaccine alone results in an insignificant rise in the activity of these effector cells, and sensitization with S. aureus produces no changes at all. The pronounced activation of the cytotoxicity of macrophages, NK and, to a lesser extent, ADK has been observed in DH reaction induced by the injection of a specific antigen into the sensitized mice. In the course of DH reaction a rise in the activity of NK and ADK not only against tumor target cells, but also against microbial ones (Candida albicans and S. aureus) has been found to occur.     

Biological and structural properties of MIP-1 alpha expressed in yeast.

The murine macrophage inflammatory proteins-1 alpha (MIP-1 alpha) and MIP-1 beta are distinct but closely related cytokines. Partially purified mixtures of the two proteins affect neutrophil function and cause local inflammation and fever. The particular properties of MIP-1 alpha have not been well studied, although it has been identified as being identical to an inhibitor of haemopoietic stem cell growth. We have expressed MIP-1 alpha in yeast cells and purified it to sequence homogeneity. Structural analysis of this biologically active material by circular dichroism and fluorescence spectroscopy confirms that MIP-1 alpha has a very similar secondary and tertiary structure to platelet factor 4 and interleukin 8 with which it shares limited sequence homology. The in-vitro stem cell inhibitory properties have been confirmed using a range of murine progenitor cells including purified bone marrow progenitor cells (FACS-1), the FDCP-mix A4 cell line, and spleen colony forming unit (CFU-S) populations. Plateau levels of inhibition of stem cell growth were achieved using concentrations of 0.15 micrograms/ml MIP-1 alpha. We have also demonstrated that MIP-1 alpha is active in vivo: 5 micrograms of MIP-1 alpha per mouse given as a bolus injection, protects stem cells from subsequent in-vitro killing by tritiated thymidine. MIP-1 alpha was also shown to enhance the proliferation of more committed progenitor granulocyte macrophage-colony forming cells (GM-CFC) in response to granulocyte macrophage-colony stimulating factor (GM-CSF).     

Serotonin Inhibits Acetylcholine Release from Rat Striatum Slices: Evidence for a Presynaptic Receptor-Mediated Effect

Rat brain striatum slices were incubated with [3H]choline, perfused with a physiological buffer, and stimulated by perfusion with a K+-enriched buffer for 2 min. The tritium overflow evoked by K+ was decreased by 5-hydroxytryptamine (serotonin, 5-HT) (maximal inhibition 10(-6) M). This effect of 5-HT was mimicked by several agonists (5-methoxytryptamine, N,N-dimethyl-tryptamine, bufotenin) and blocked by serotonergic antagonists (methiothepin, methysergide, cinanserin) but not by haloperidol; methiothepin and methysergide alone slightly increased the K+-evoked overflow of tritium (3H). Inhibition of the tritium release by 5-HT was not suppressed in the presence of tetrodotoxin (TTX) (10(-6) M). These results suggest that 5-HT tonically inhibits acetylcholine (ACh) release from striatal cholinergic neurons by acting on a presynaptic receptor localized on cholinergic terminals.