Chloroform markedly stimulates the phosphorylation of myelin basic proteins

A mixture of environmental contaminants increases cAMP-dependent protein kinase in Spisula embryos

Using the surf clam embryo, we investigated the effects of the combination of bromoform, chloroform, and tetrachloroethylene, three pollutants found in high concentrations in the municipal water supply in Brick, New Jersey. Exposure produced an increase in an isoform of the regulatory subunit (RII) of cAMP-dependent protein kinase, demonstrated by confocal microscopy and western blotting. Embryos showed an increase in RII where the primordial gill and ciliated velar epithelium are innervated. This increase correlated with increased ciliary activity, indicating a corresponding rise in the catalytic subunit. Treatment resulted in decreased threonine phosphorylation of actin. There was no effect on neurotransmitters or receptors of the serotonergic-dopaminergic nervous system. These effects occurred only with the ternary mixture. No significant effect was seen with individual or paired components. This is the first report showing that bromoform, chloroform, and tetrachloroethylene act synergistically to alter a key regulator of neuronal development.

Myelin basic protein-diverse conformational states of an intrinsically unstructured protein and its roles in myelin assembly and multiple sclerosis

The 18.5 kDa isoform of myelin basic protein (MBP) is a major component of the myelin sheath in the central nervous system of higher vertebrates, and a member of a larger family of proteins with a multiplicity of forms and post-translational modifications (PTMs). The 18.5 kDa protein is the exemplar of the family, being most abundant in adult myelin, and thus the most-studied. It is peripherally membrane-associated, but has generally been investigated in isolated form. MBP is an 'intrinsically unstructured' protein with a high proportion (approximately 75%) of random coil, but postulated to have core elements of beta-sheet and alpha-helix. We review here the properties of the MBP family, especially of the 18.5 kDa isoform, and discuss how its three-dimensional (3D) structure may be resolved by direct techniques available to us, viz., X-ray and electron crystallography, and solution and solid-state NMR spectrometry. In particular, we emphasise that creating an appropriate environment in which the protein can adopt a physiologically relevant fold is crucial to such endeavours. By solving the 3D structure of 18.5 kDa MBP and the effects of PTMs, we will attain a better understanding of myelin architecture, and of the molecular mechanisms that transpire in demyelinating diseases such as multiple sclerosis.

The structure and function of central nervous system myelin

Multiple sclerosis (MS) is characterized by the active degradation of central nervous system myelin, a multilamellar membrane system that insulates nerve axons. MS arises from complex interactions between genetic, immunological, infective, and biochemical mechanisms. Although the circumstances of MS etiology remain hypothetical, one persistent theme involves immune system recognition of myelin-specific antigens derived from myelin basic protein, the most abundant extrinsic myelin membrane protein, and/or another equally suitable myelin protein or lipid. Knowledge of the biochemical and physical-chemical properties of myelin proteins, and lipids, particularly their composition, organization, structure, and accessibility with respect to the compacted myelin multilayers, thus becomes central to understanding how and why these antigens become selected during the development of MS. This article focuses on the current understanding of the molecular basis of MS as it may relate to the protein and lipid components of myelin, which dictate myelin morphology on the basis of protein-lipid and lipid-lipid interactions, and the relationship, if any, between the protein/lipid components and the destruction of myelin in pathological situations.

Protein kinase C in rat brain myelin

It has been suggested that phosphorylation of myelin basic protein (MBP) in CNS is catalyzed by protein kinase C (PKC). In order to demonstrate that PKC in the myelin phosphorylates MBP, PKC was partially purified from rat CNS myelin by solubilization with Triton X-100 followed by a DEAE-cellulose column. MBP and histone III-S were phosphorylated in the presence of Ca2+ and phospholipid by rat myelin PKC. High voltage electrophoresis revealed that the phosphoamino acids in MBP by this kinase was serine residue, which is known to be the amino acid phosphorylated by PKC. The activity of PKC extracted from myelin was inhibited by the addition of psychosine to the incubation mixture. To confirm the presence of PKC molecule and to identify the isoform of PKC in the myelin, the solubilized myelin fraction was applied on SDS-PAGE, transferred to a nitrocellulose sheet and stained with anti-PKC monoclonal antibodies. Rat CNS myelin contained the PKC of about 80 kDa (intact PKC), and no proteolytic fragments were observed. PKC isozymes in myelin were type II and III. A developmental study from 14 to 42 postnatal days showed that PKC activity in CNS myelin seemed to parallel the deposition of myelin protein.

Is myelin basic protein crystallizable?

Myelin basic protein (MBP) is the predominant extrinsic protein in both central and peripheral nervous system myelins. It is thought to be involved in the stabilizing interactions between myelin membranes, and it may play an important role in demyelinating diseases such as multiple sclerosis. In spite of the fact that this abundant protein has been known for almost three decades, its three-dimensional crystal structure has not yet been determined. In this study we report on our extensive attempts to crystallize the major 18.5 kDa isoform of MBP. We used MBP having different degrees of purity, ranging from crude MBP (that was acid or salt extracted from isolated myelin), to highest purity single isoform. We used convention strategies in our search for a suitable composition of a crystallization medium. We applied both full and incomplete factorial searches for crystallization conditions. We analyzed the available data on proteins which have previously resisted crystallization, and applied this information to our own experiments. Nevertheless, despite our efforts which included 4600 different conditions, we were unable to induce crystallization of MBP. Previous work on MBP indicates that when it is removed from its native environment in the myelin membrane and put in crystallization media, the protein adopts a random coil conformation and persists as a population of structurally non-identical molecules. This thermodynamically preferred state presumably hinders crystallization, because the most fundamental factor of protein crystallization - homogeneity of tertiary structure--is lacking. We conclude that as long as its random coil flexibility is not suppressed, 18.5 kDa MBP and possibly also its isoforms will remain preeminent examples of proteins that cannot be crystallized.

Central nervous system myelin: structure, function, and pathology

Multiple sclerosis (MS) and a number of related distinctive diseases are characterized by the active degradation of central nervous system (CNS) myelin, an axonal sheath comprised essentially of proteins and lipids. These demyelinating diseases appear to arise from complex interactions of genetic, immunological, infective, and biochemical mechanisms. While circumstances of MS etiology remain hypothetical, one persistent theme involves recognition by the immune system of myelin-specific antigens derived from myelin basic protein (MBP), the most abundant extrinsic myelin membrane protein, and/or another equally susceptible myelin protein or lipid component. Knowledge of the biochemical and physical-chemical properties of myelin proteins and lipids, particularly their composition, organization, structure, and accessibility with respect to the compacted myelin multilayers, thus becomes central to the understanding of how and why these antigens become selected during the development of MS. This review focuses on current understanding of the molecular basis underlying demyelinating disease as it may relate to the impact of the various protein and lipid components on myelin morphology; the precise molecular architecture of this membrane as dictated by protein-lipid and lipid-lipid interactions; and the relationship, if any, between the protein/lipid components and the destruction of myelin in pathological situations.

Accumulation of galactosylsphingosine (psychosine) does not interfere with phosphorylation and methylation of myelin basic protein in the twitcher mouse

In attempts to elucidate mechanisms of demyelination in the twitcher mouse (Twi), phosphorylation and methylation of myelin basic protein (MBP) were examined in the brainstem and spinal cord of this species. Phosphorylation of MBP in isolated myelin by an endogenous kinase and an exogenous [32P]ATP was not impaired and protein kinase C activity in the brain cytosol was not reduced. When the methylation of an arginine residue of MBP was examined in slices of the brainstem and spinal cord, using [3H]methionine as a donor of the methyl groups, no difference was found between Twi and the controls. Radioactivity of the [3H] methionine residue of MBP of Twi was also similar to that of the controls. Thus, accumulation of psychosine in Twi does not interfere with the activity of endogenous kinase, methylation of MBP, and the synthesis and transport of MBP into myelin membrane.

Tumor promoters accentuate phosphorylation of PO: evidence for the presence of protein kinase C in purified PNS myelin

The effects of carbon tetrachloride, methylene chloride and chloroform on phosphorylation of PO was examined. The results of the dose response curve revealed that carbon tetrachloride (0.67%), methylene chloride (2%) and chloroform (1%) induced phosphorylation of PO by approximately 4, 6, and 12-fold, respectively. PO was found to be phosphorylated on the serine residue, and the phosphorylation of the serine residue was markedly increased when PO was phosphorylated in the presence of these compounds. Since tumor promoters, carbon tetrachloride and chloroform, have been shown to activate protein kinase C in platelets it is postulated that the increased phosphorylation of PO may result from the activation of myelin associated protein kinase C. The presence of phospholipid sensitive Ca2+-dependent protein kinase (protein kinase C) in in purified nerve myelin was demonstrated by increased phosphorylation of PO in the presence of Ca2+ and phosphatidylserine.