Serotonin binding sites. I. Structures of sites on myelin basic protein, LHRH, MSH, ACTH, interferon, serum albumin, ovalbumin and red pigment concentrating hormone

A modular hierarchy-based theory of the chemical origins of life based on molecular complementarity

Albert Szent-Gyorgyi once defined discovery as seeing what everyone else sees and thinking what no one else thinks. I often find that phenomena that are obvious to other people are not obvious to me. Molecular complementarity is one of these phenomena: while rare among any random set of compounds, it is ubiquitous in living systems. Because every molecule in a living system binds more or less specifically to several others, we now speak of "interactomes". What explains the ubiquity of molecular complementarity in living systems? What might such an explanation reveal about the chemical origins of life and the principles that have governed its evolution? Beyond this, what might complementarity tell us about the optimization of integrated systems in general? My research combines theoretical and experimental approaches to molecular complementarity relating to evolution from prebiotic chemical systems to superorganismal interactions. Experimentally, I have characterized complementarity involving specific binding between small molecules and explored how these small-molecule modules have been incorporated into macromolecular systems such as receptors and transporters. Several general principles have emerged from this research. Molecules that bind to each other almost always alter each other's physiological effects; and conversely, molecules that have antagonistic or synergistic physiological effects almost always bind to each other. This principle suggests a chemical link between biological structure and function. Secondly, modern biological systems contain an embedded molecular paleontology based on complementarity that can reveal their chemical origins. This molecular paleontology is often manifested through modules involving small, molecularly complementary subunits that are built into modern macromolecular structures such as receptors and transporters. A third principle is that complementary modules are conserved and repurposed at every stage of evolution. Molecular complementarity plays critical roles in the evolution of chemical systems and resolves a significant number of outstanding problems in the emergence of complex systems. All physical and mathematical models of organization within complex systems rely upon nonrandom linkage between components. Molecular complementarity provides a naturally occurring nonrandom linker. More importantly, the formation of hierarchically organized stable modules vastly improves the probability of achieving self-organization, and molecular complementarity provides a mechanism by which hierarchically organized stable modules can form. Finally, modularity based on molecular complementarity produces a means for storing and replicating information. Linear replicating molecules such as DNA or RNA are not required to transmit information from one generation of compounds to the next: compositional replication is as ubiquitous in living systems as genetic replication and is equally important to its functions. Chemical systems composed of complementary modules mediate this compositional replication and gave rise to linear replication schemes. In sum, I propose that molecular complementarity is ubiquitous in living systems because it provides the physicochemical basis for modular, hierarchical ordering and replication necessary for the evolution of the chemical systems upon which life is based. I conjecture that complementarity more generally is an essential agent that mediates evolution at every level of organization.

Molecular mimicry revisited: gut bacteria and multiple sclerosis

Molecular mimicry is a possible explanation for autoimmune side effects of microorganism infections. Protein sequences from a particular microorganism are compared to known autoimmune immunogens. For diseases such as multiple sclerosis (MS), where the infectious agent is unknown, guesses to its identity are made. Mimics are assumed to be rare. This study takes a radically different approach. Reported sequences from all known human bacterial and viral agents were searched for autoimmune immunogen mimics. Three encephalitogenic peptides, whose autoimmune requirements have been studied extensively, were selected for comparison. Mimics were seen in a wide variety of organisms. For each immunogen, the mimics were found predominantly in nonpathogenic gut bacteria. Since the three immunogens used in this study are related to MS, it is suggested that a microorganism responsible for autoimmune activity in MS could be a normally occurring gut bacterium. This would explain many of the peculiar MS epidemiological data and why no infective agent has been identified for MS and supports recently found MS gut metabolism abnormalities.

Compositional complementarity and prebiotic ecology in the origin of life

We hypothesize that life began not with the first self-reproducing molecule or metabolic network, but as a prebiotic ecology of co-evolving populations of macromolecular aggregates (composomes). Each composome species had a particular molecular composition resulting from molecular complementarity among environmentally available prebiotic compounds. Natural selection acted on composomal species that varied in properties and functions such as stability, catalysis, fission, fusion and selective accumulation of molecules from solution. Fission permitted molecular replication based on composition rather than linear structure, while fusion created composomal variability. Catalytic functions provided additional chemical novelty resulting eventually in autocatalytic and mutually catalytic networks within composomal species. Composomal autocatalysis and interdependence allowed the Darwinian co-evolution of content and control (metabolism). The existence of chemical interfaces within complex composomes created linear templates upon which self-reproducing molecules (such as RNA) could be synthesized, permitting the evolution of informational replication by molecular templating. Mathematical and experimental tests are proposed.

Molecular mimicry or structural mimicry?

"Molecular mimicry" should be changed to "structural mimicry". The immune system recognizes shapes--three-dimensional shapes--not sequences. For two sequences to act biologically similar they must possess similar three-dimensional structures.

Peptide self-aggregation and peptide complementarity as bases for the evolution of peptide receptors: a review

This paper reviews the three major theories of peptide receptor evolution: (1) Dwyer's theory that peptide receptors evolved from self-aggregating peptides; (2) Root-Bernstein's theory that peptide receptors evolved from functionally and structurally complementary peptides; and (3) Blalock's theory that receptors evolved from hydropathically complementary sequences encoded in the antisense strand of the DNA encoding each peptide. The evidence to date suggests that the co-yevolution of peptides and their receptors is strongly constrained by one or more of these physicochemically based mechanisms, which argues against a random or frozen accident' model. The data also suggest that structure and function are integrally related from the earliest steps of receptor-ligand evolution so that peptide functionality is non-random and highly conserved in its origin. The result is a molecular paleontology' that reveals the evolutionary constraints that shaped the interaction of structure and function.

Chronic barium intoxication disrupts sulphated proteoglycan synthesis: a hypothesis for the origins of multiple sclerosis

High level contamination by natural and industrial sources of the alkali earth metal, barium (Ba) has been identified in the ecosystems/workplaces that are associated with high incidence clustering of multiple sclerosis (MS) and other neurodegenerative diseases such as the transmissible spongiform encephalopathies (TSEs) and amyotrophic lateral sclerosis (ALS). Analyses of ecosystems supporting the most renowned MS clusters in Saskatchewan, Sardinia, Massachusetts, Colorado, Guam, NE Scotland demonstrated consistently elevated levels of Ba in soils (mean: 1428 ppm) and vegetation (mean: 74 ppm) in relation to mean levels of 345 and 19 ppm recorded in MS-free regions adjoining. The high levels of Ba stemmed from local quarrying for Ba ores and/or use of Ba in paper/foundry/welding/textile/oil and gas well related industries, as well as from the use of Ba as an atmospheric aerosol spray for enhancing/refracting the signalling of radio/radar waves along military jet flight paths, missile test ranges, etc. It is proposed that chronic contamination of the biosystem with the reactive types of Ba salts can initiate the pathogenesis of MS; due to the conjugation of Ba with free sulphate, which subsequently deprives the endogenous sulphated proteoglycan molecules (heparan sulfates) of their sulphate co partner, thereby disrupting synthesis of S-proteoglycans and their crucial role in the fibroblast growth factor (FGF) signalling which induces oligodendrocyte progenitors to maintain the growth and structural integrity of the myelin sheath. Loss of S-proteoglycan activity explains other key facets of MS pathogenesis; such as the aggregation of platelets and the proliferation of superoxide generated oxidative stress. Ba intoxications disturb the sodium-potassium ion pump--another key feature of the MS profile. The co-clustering of various neurodegenerative diseases in these Ba-contaminated ecosystems suggests that the pathogenesis of all of these diseases could pivot upon a common disruption of the sulphated proteoglycan-growth factor mediated signalling systems. Individual genetics dictates which specific disease emerges at the end of the day.

Autoantibodies against alpha -MSH, ACTH, and LHRH in anorexia and bulimia nervosa patients

The hypothalamic arcuate nucleus is involved in the control of energy intake and expenditure and may participate in the pathogenesis of eating disorders such as anorexia nervosa (AN) and bulimia nervosa (BN). Two systems are of particular interest in this respect, synthesizing alpha-melanocyte-stimulating hormone (alpha-MSH) and synthesizing neuropeptide Y, respectively. We report here that 42 of 57 (74%) AN andor BN patients studied had in their plasma Abs that bind to melanotropes andor corticotropes in the rat pituitary. Among these sera, 8 were found to bind selectively to alpha-MSH-positive neurons and their hypothalamic and extrahypothalamic projections as revealed with immunostaining on rat brain sections. Adsorption of these sera with alpha-MSH peptide abolished this immunostaining. In the pituitary, the immunostaining was blocked by adsorption with alpha-MSH or adrenocorticotropic hormone. Additionally, 3 ANBN sera bound to luteinizing hormone-releasing hormone (LHRH)-positive terminals in the rat median eminence, but only 2 of them were adsorbed with LHRH. In the control subjects, 2 of 13 sera (16%) displayed similar to ANBN staining. These data provide evidence that a significant subpopulation of ANBN patients have autoantibodies that bind to alpha-MSH or adrenocorticotropic hormone, a finding pointing also to involvement of the stress axis. It remains to be established whether these Abs interfere with normal signal transduction in the brain melanocortin circuitryLHRH system andor in other central and peripheral sites relevant to food intake regulation, to what extent such effects are related to andor could be involved in the pathophysiology or clinical presentation of ANBN, and to what extent increased stress is an important factor for production of these autoantibodies.

Molecular complementarity III. peptide complementarity as a basis for peptide receptor evolution: a bioinformatic case study of insulin, glucagon and gastrin

Dwyer has suggested that peptide receptors evolved from self-aggregating peptides so that peptide receptors should incorporate regions of high homology with the peptide ligand. If one considers self-aggregation to be a particular manifestation of molecular complementarity in general, then it is possible to extend Dwyer's hypothesis to a broader set of peptides: complementary peptides that bind to each other. In the latter case, one would expect to find homologous copies of the complementary peptide in the receptor. Thirteen peptides, 10 of which are not known to self-aggregate (amylin, ACTH, LHRH, angiotensin II, atrial natriuretic peptide, somatostatin, oxytocin, neurotensin, vasopressin, and substance P), and three that are known to self-aggregate (insulin, glucagon, and gastrin), were chosen. In addition to being self-aggregating, insulin and glucagon are also known to bind to each other, making them a mutually complementary pair. All possible combinations of the 13 peptides and the extracellular regions of their receptors were investigated using bioinformatic tools (a total of 325 combinations). Multiple, statistically significant homologies were found for insulin in the insulin receptor; insulin in the glucagon receptor; glucagon in the glucagon receptor; glucagon in the insulin receptor; and gastrin in gastrin binding protein and its receptor. Most of these homologies are in regions or sequences known to contribute to receptor binding of the respective hormone. These results suggest that the Dwyer hypothesis for receptor evolution may be generalizable beyond self-aggregating to complementary peptides. The evolution of receptors may have been driven by small molecule complementarity augmented by modular evolutionary processes that left a "molecular paleontology" that is still evident in the genome today. This "paleontology" may allow identification of peptide receptor sites.

The basic protein of CNS myelin: its structure and ligand binding

Consideration of the evidence presented in this review leads to the following conclusions: (a) Isolated MBP in aqueous solution has little ordered secondary or tertiary structure. (b) In this state, the protein can associate with a wide range of hydrophobic and amphiphilic compounds, these interactions involving limited sections of the protein. (c) The strength of binding to bilayers and the accompanying conformational changes in the protein are greatest for systems containing acidic lipids, presumably because of the involvement of ionic interactions. (d) When bound to bilayers of acidic lipids, MBP will have substantially more ordered secondary structure than it manifests in aqueous solution, and it is likely to be oligomeric (possibly hexameric). (e) MBP does affect the organization of lipid aggregates. It influences strongly the separation of bilayers in multilayers of purified lipids, and at present this must be viewed as its prime role within myelin. The greatest impediment to our understanding of MBP is the lack of an assayable biological activity. In contrast to the situation with enzymes, for example, we have no functional test for changes in protein structure or changes accompanying interactions with other molecules. Current evidence suggests that the protein has a structural role within myelin and that its own three-dimensional structure is strongly dependent on the molecules with which it is associated. If this picture is correct, studies of the isolated protein or of the protein in reconstituted lipid systems may yield, at best, a rough guide to the structure within its biological environment. Further clarification of the structure and function of MBP may have to await development of more powerful techniques for studying proteins bound to large molecular aggregates, such as lipid bilayers. The paucity of generally applicable methods is reflected in the fact that even low resolution structures are known for only a handful of intrinsic membrane proteins, and even more limited information exists for proteins associated with membrane surfaces. However, the increasing use of a combination of electron microscopy and diffraction on two-dimensional arrays of proteins formed on lipid bilayers (Henderson et al., 1990) offers the hope that it may not be too long before it will be possible to study at moderate resolution the three-dimensional structure of MBP bound to a lipid membrane.

An introduction to the possible role of central nervous system structures in neuroendocrine-immune systems interaction

The involvement of different regions of the brain in the immune response was investigated with the aid of small electrolytic lesions. The lesions were placed in such a way that they covered different areas of the brain stem, basal ganglia, but also some parts of the frontal cortex. The cellular immune response as well as DNA synthesis with the aid of labelled precursors was measured. The results suggest the possibility of the existence of three circuits. One circuit represents catecholaminergic cell group A1-7 in reticular formation, nucleus parabrachialis and central ncl. amygdalae. The second circuit represents serotonergic rapheal groups B6.8, hypothalamus and ncl. basomedialis of amygdala. The third circuit represents ncl. amygdalae and the medial part of frontal cortex, namely the cingulate cortex area 1-2. The close correlation between the changes of the immune response and the CNS activity was also investigated in the experiments with immunosuppressed and immunostimulated animals by measuring of the turnover of some neurotransmitters but also by recording electrocephalographic activity.

Hyperserotoninemia and antiserotonin antibodies in autism and other disorders

This study examined the linkage between elevated blood serotonin in autism and the presence of circulating autoantibodies against the serotonin 5HT1A receptor. Information was also obtained on the diagnostic and receptor specificity of these autoantibodies. Blood serotonin was measured as was inhibition of serotonin binding to human cortical membranes by antibody-rich fractions of blood from controls and from patients with childhood autism, schizophrenia, obsessive-compulsive disorder, Tourette's, and multiple sclerosis. The results showed elevated blood serotonin was not closely related to inhibition of serotonin binding by antibody-rich blood fractions. Inhibition of binding was highest for patients with multiple sclerosis and was not specific to the 5HT1A receptor as currently defined. Although inhibition was not specific to autism, the data were insufficient to establish if people with autism differed from normal controls on this measure.

Role of biological membranes in slow-wave sleep

Two involvements of cellular membranes in slow-wave sleep (SWS) are discussed. In the first the endoplasmic reticulum (ER) is focussed upon, and in the second, the plasmalemma, where specific binding sites (receptors?) for promoters of slow-wave sleep are believed to be located. The study concerning the ER focuses on an enzyme in the brain, glucose-6-phosphatase, which, although present at low levels, manifests greatly increased activity during SWS compared to the waking state. The work on the plasmalemma has to do with the specific binding of muramyl peptides, inducers of slow-wave sleep, to various cells, and membrane preparations of various sorts, including those from brain tissue. Such cells as macrophages from mice, B-lymphocytes from human blood, and cells from a cell line (C-6 glioma) have been examined in this context.

Peptide displacement of [3H]5-hydroxytryptamine binding to bovine cortical membranes

Chemical studies have demonstrated that peptides such as the encephalitogenic (EAE) peptide of myelin basic protein (MBP) and luteinizing hormone-releasing hormone (LHRH) can bind serotonin (5-hydroxytryptamine, 5-HT) in vitro. The present research was undertaken to determine whether such binding interferes with 5-HT binding to its 5-HT1 receptors on bovine cerebral cortical membranes. EAE peptide and LHRH displaced [3H]5-HT with IC50s of 4.0 x 10(-4) and 1.8 x 10(-3) M respectively. MBP itself also showed apparent displacing ability with an IC50 of 6.0 x 10(-5) M, though it also caused aggregation of cortical membranes that might have interfered with normal receptor binding. These results support previous suggestions that the tryptophan peptide region of MBP may act as a 5-HT receptor in the neural system. We also tested the effects of muramyl dipeptide (N-acetyl-muramyl-L-Ala-D-isoGln, MD), a bacterial cell-wall breakdown product that acts as a slow-wave sleep promoter, binds to LHRH and EAE peptide, and competes for 5-HT binding sites on macrophages. It showed no significant displacement of 5-HT binding to cortical membranes (IC50 greater than 10(-1) M), but its D-Ala analogue did (IC50 = 1.7 x 10(-3) M). Thus, it seems likely that the 5-HT-related effects of naturally occurring muramyl peptides are physiologically limited by receptor types.

Serotonin binding sites. II. Muramyl dipeptide binds to serotonin binding sites on myelin basic protein, LHRH, and MSH-ACTH 4-10

Previously, we reported the existence of structurally similar serotonin binding sites on myelin basic protein, LHRH, and MSH-ACTH 4-10. We now report that the adjuvant peptide, muramyl dipeptide (N-acetyl-muramyl-L-Ala-D-isoGln) also binds to these sites. This observation may help to explain previous observations of serotonin-like activity by muramyl peptides, including the promotion of slow-wave sleep and fever induction. The observation may also provide an important link between the immune system and the nervous system that may explain the role of muramyl dipeptide adjuvants in causing autoimmune diseases to serotonin-regulated proteins and their receptors, as well as the alterations in serotonin levels that are often observed in autoimmune diseases. The observation provides concrete evidence for a dual-antigen hypothesis for the induction of autoimmune diseases by an adjuvant-peptide complex. Application of such a mechanism for induction of autoimmunity may be of importance in understanding a number of postinfectious and postvaccinal neuropathies, and suggests a possible etiology for autism, in which many patients have high blood serotonin levels, autoimmune reactions to myelin basic protein, and antibodies to serotonin binding sites. Finally, the observation suggests that glycopeptides may act as neurotransmitters.

Catecholamines bind to enkephalins, morphiceptin, and morphine

Nuclear magnetic resonance spectroscopy, pH titration, and color reactions demonstrate that the catecholamines dopamine, epinephrine, and norepinephrine bind to the enkephalins. Binding constants are c. 6 X 10(3) per mole. Catecholamines also bound to the mu opiate receptor agonist morphiceptin (Tyr-Pro-Phe-Pro-NH2). Very little binding was found to enkephalin and morphiceptin fragments and analogues, indicating that the entire molecules are necessary. Serotonin binding peptides do not bind the catecholamines. Morphine and apomorphine, however, do bind these catecholamines (with a binding constant for morphine of c. 4 X 10(4) per mole). The opiate antagonist naloxone and a number of other drugs do not bind catecholamines. Morphine, morphiceptin, and the enkephalins also retard the formation of colored reaction products by catecholamines in vitro. These results may help to explain observations that the enkephalins are co-stored and co-transmitted with dopamine and norepinephrine, and may provide a basis for the elucidation of other known cases of peptide-monoamine co-transmission. Possible implications for understanding opiate effects on catecholamines during addiction and withdrawal are discussed, and suggestions concerning drug design are made.

Determination of serotonin in whole blood, platelet-rich plasma, platelet-poor plasma and plasma ultrafiltrate

The important biogenic amine, serotonin (5HT), was determined in whole blood, platelet-rich plasma (PRP), platelet-poor plasma (PPP), and plasma ultrafiltrate after simple deproteinization. Following ion-pair chromatography on standard or narrow-bore reverse-phase columns, 5HT and the internal standard (N-methylserotonin-NMS) were detected by fluorometry with absolute detection limits of 2-4 pg. Levels obtained for whole blood and PRP were in agreement with previous methods. However, mean (+/- SD) values obtained for platelet-poor plasma (PPP) of 578 +/- 277 pg/ml (N = 7) were approximately 3-fold lower than the lowest previous reports. We also report the first determination of 5HT in plasma ultrafiltrate, having observed mean levels of 387 +/- 222 pg/ml (N = 7).

Noradrenergic sympathetic innervation of the spleen: I. Nerve fibers associate with lymphocytes and macrophages in specific compartments of the splenic white pulp

Sympathetic noradrenergic nerve fibers, stained with antiserum for tyrosine hydroxylase (TH), richly innervate the splenic white pulp. These fibers distribute with the vascular and trabecular systems, and associate mainly with the central artery and its branches, the periarteriolar lymphatic sheath (PALS), the marginal sinus, and the parafollicular zone, with occasional delicate fibers also present in the follicles. Simultaneous staining of TH-positive nerve fibers and markers for specific lymphoid cells has shown several regions of contact between nerves and lymphocytes or macrophages. The TH-positive nerve fibers in the plexuses around the central arterial system and in the PALS are present among T lymphocytes (OX-19-positive cells) including both T helper and T suppressor cells, and interdigitating cells. At the marginal sinus, TH-positive fibers run adjacent to macrophages (ED3-positive cells), B lymphocytes (IgM-positive), and intensely fluorescent IgM-positive cells. Along the parafollicular zone, TH-positive nerve fibers run adjacent to T lymphocytes, peripheral follicular B lymphocytes, and intensely fluorescent IgM-positive cells. Within some follicles, delicate fibers end adjacent to both T and B lymphocytes. These relationships suggest a direct interaction between norepinephrine release from the TH-positive nerve terminals and the lymphocytes and macrophages closely associated with them, and focuses attention on the potential neural modulation of related functions such as T and B lymphocyte entry into the spleen and antigen capture (marginal zone), antigen presentation and T cell activation (PALS), B cell activation (parafollicular zone and marginal zone), and lymphocyte egress (outer marginal zone).

Bovine pineal antireproductive tripeptide binds to luteinizing hormone-releasing hormone: a model for peptide modulation by sequence specific peptide interactions?

We report results of chromatographic, pH titration and nuclear magnetic resonance (NMR) spectroscopy studies demonstrating that the bovine pineal antireproductive tripeptide, Thr-Ser-Lys (BPART), binds to luteinizing hormone-releasing hormone (LHRH) at a site comprised of LHRH 2-5 (His-Trp-Ser-Tyr). BPART and LHRH have been shown to be antagonists in vitro. The binding constant is ca. 2 X 10(3)/mole. An NMR study of fifty other peptide pairs demonstrates that the binding is sequence and residue specific. The binding provides evidence of the amino acid pairing hypothesis, and suggests the possibility of modulation of one peptide by directly binding with another peptide.