Profiling disease burden and Borrelia seroprevalence in Canadians with complex and chronic illness.

Lyme disease, caused by vector-borne Borrelia bacteria, can present with diverse multi-system symptoms that resemble other conditions. The objective of this study was to evaluate disease presentations and Borrelia seroreactivity in individuals experiencing a spectrum of chronic and complex illnesses. We recruited 157 participants from Eastern Canada who reported one or more diagnoses of Lyme disease, neurological, rheumatic, autoimmune, inflammatory, gastrointestinal, or cardiovascular illnesses, or were asymptomatic and presumed healthy. Intake categories were used to classify participants based on their perceived proximity to Lyme disease, distinguishing between those with a disclosed history of Borrelia infection, those with lookalike conditions (e.g. fibromyalgia syndrome), and those with unrelated ailments (e.g. intestinal polyps). Participants completed three questionnaires, the SF-36 v1, SIQR, and HMQ, to capture symptoms and functional burden, and provided blood serum for analysis at an accredited diagnostic lab. Two-tiered IgG and IgM serological assessments (whole cell ELISA and Western blot) were performed in a blinded fashion on all samples. The pattern of symptoms and functional burden were similarly profound in the presumptive Lyme and Lyme-like disease categories. Borrelia seroprevalence across the study cohort was 10% for each of IgG and IgM, and occurred within and beyond the Lyme disease intake category. Western blot positivity in the absence of reactive ELISA was also substantial. Fibromyalgia was the most common individual diagnostic tag disclosed by two-tier IgG-positive participants who did not report a history of Lyme disease. Within the IgG seropositive cohort, the presence of antibodies against the 31 kDa Outer Surface Protein A (OspA) was associated with significantly better health outcomes. Previously, this marker has been linked to treatment-refractory Lyme arthritis. Overall, our findings support prior observations of phenotypic overlap between Lyme and other diseases. Seropositivity associated with non-specific symptoms and functional impairment warrants further mechanistic investigation and therapeutic optimization.

α-Synuclein mutation impairs processing of endomembrane compartments and promotes exocytosis and seeding of α-synuclein pathology.

Neuronal loss in Parkinson's disease (PD) is associated with impaired proteostasis and accumulation of α-syn microaggregates in dopaminergic neurons. These microaggregates promote seeding of α-synuclein (α-syn) pathology between synaptically linked neurons. However, the mechanism by which seeding is initiated is not clear. Using human pluripotent stem cell (hPSC) models of PD that allow comparison of SNCA mutant cells with isogenic controls, we find that SNCA mutant neurons accumulate α-syn deposits that cluster to multiple endomembrane compartments, specifically multivesicular bodies (MVBs) and lysosomes. We demonstrate that A53T and E46K α-syn variants bind and sequester LC3B monomers into detergent-insoluble microaggregates on the surface of late endosomes, increasing α-syn excretion via exosomes and promoting seeding of α-syn from SNCA mutant neurons to wild-type (WT) isogenic controls. Finally, we show that constitutive inactivation of LC3B promotes α-syn accumulation and seeding, while LC3B activation inhibits these events, offering mechanistic insight into the spread of synucleinopathy in PD.

Partial magic angle spinning NMR 1H, 13C, 15N resonance assignments of the flexible regions of a monomeric alpha-synuclein: conformation of C-terminus in the lipid-bound and amyloid fibril states.

Alpha-synuclein (α-syn) is a small presynaptic protein that is believed to play an important role in the pathogenesis of Parkinson's disease (PD). It localizes to presynaptic terminals where it partitions between a cytosolic soluble and a lipid-bound state. Recent evidence suggests that α-syn can also associate with mitochondrial membranes where it interacts with a unique anionic phospholipid cardiolipin (CL). Here, we examine the conformation of the flexible fragments of a monomeric α-syn bound to lipid vesicles composed of anionic 1,2-dioleoyl-sn-glycero-3-phosphate (DOPA) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipids, of tetraoleoyl CL (TOCL) and DOPC, and of fibrils. The dynamic properties of α-syn associated with DOPA:DOPC vesicles were the most favorable for conducting three-dimensional NMR experiments, and the 13C, 15N and amide 1H chemical shifts of the flexible and disordered C-terminus of α-syn could be assigned using three-dimensional through-bond magic angle spinning NMR spectroscopy. Although the C-terminus is more dynamically constrained in fibrils and in α-syn bound to TOCL:DOPC vesicles, a direct comparison of carbon chemical shifts detected using through bond two-dimensional spectroscopy indicates that the C-terminus is flexible and unstructured in all the three samples.

Niche-dependent inhibition of neural stem cell proliferation and oligodendrogenesis is mediated by the presence of myelin basic protein.

Neural stem and progenitor cells (collectively termed neural precursor cells [NPCs]) are found along the ventricular neuraxis extending from the spinal cord to the forebrain in regionally distinct niches comprised of different cell types, architecture, and cell-cell interactions. An understanding of the factors that regulate NPC behavior is critical for developing therapeutics to repair the injured central nervous system. Herein, we demonstrate that myelin basic protein (MBP), the major cytoplasmic protein constituent of the myelin sheath in oligodendrocytes, can regulate NPC behavior. Under physiological conditions, NPCs are not in contact with intracellular MBP; however, upon injury, MBP is released into the neural parenchyma. We reveal that MBP presented in a spinal cord niche is inhibitory to NPC proliferation. This inhibitory effect is regionally distinct as spinal cord NPCs, but not forebrain-derived NPCs, are inhibited by MBP. We performed coculture and conditioned media experiments that reveal the stem cell niche is a key regulator of MBP's inhibitory actions on NPCs. The inhibition is mediated by a heat-labile protein released by spinal cord niche cells, but not forebrain niche cells. However, forebrain NPCs are also inhibited by the spinal cord derived factor as revealed following in vivo infusion of the spinal cord niche-derived conditioned media. Moreover, we show that MBP inhibits oligodendrogenesis from NPCs. Together, these findings highlight the role of MBP and the regionally distinct microenvironment in regulating NPC behavior which has important implications for stem cell-based regenerative strategies.

Lyme Disease Frontiers: Reconciling Borrelia Biology and Clinical Conundrums.

Lyme disease is a complex tick-borne zoonosis that poses an escalating public health threat in several parts of the world, despite sophisticated healthcare infrastructure and decades of effort to address the problem. Concepts like the true burden of the illness, from incidence rates to longstanding consequences of infection, and optimal case management, also remain shrouded in controversy. At the heart of this multidisciplinary issue are the causative spirochetal pathogens belonging to the Borrelia Lyme complex. Their unusual physiology and versatile lifestyle have challenged microbiologists, and may also hold the key to unlocking mysteries of the disease. The goal of this review is therefore to integrate established and emerging concepts of Borrelia biology and pathogenesis, and position them in the broader context of biomedical research and clinical practice. We begin by considering the conventions around diagnosing and characterizing Lyme disease that have served as a conceptual framework for the discipline. We then explore virulence from the perspective of both host (genetic and environmental predispositions) and pathogen (serotypes, dissemination, and immune modulation), as well as considering antimicrobial strategies (lab methodology, resistance, persistence, and clinical application), and borrelial adaptations of hypothesized medical significance (phenotypic plasticity or pleomorphy).

Cardiolipin exposure on the outer mitochondrial membrane modulates α-synuclein.

Neuronal loss in Parkinson's disease (PD) is associated with aberrant mitochondrial function and impaired proteostasis. Identifying the mechanisms that link these pathologies is critical to furthering our understanding of PD pathogenesis. Using human pluripotent stem cells (hPSCs) that allow comparison of cells expressing mutant SNCA (encoding α-synuclein (α-syn)) with isogenic controls, or SNCA-transgenic mice, we show that SNCA-mutant neurons display fragmented mitochondria and accumulate α-syn deposits that cluster to mitochondrial membranes in response to exposure of cardiolipin on the mitochondrial surface. Whereas exposed cardiolipin specifically binds to and facilitates refolding of α-syn fibrils, prolonged cardiolipin exposure in SNCA-mutants initiates recruitment of LC3 to the mitochondria and mitophagy. Moreover, we find that co-culture of SNCA-mutant neurons with their isogenic controls results in transmission of α-syn pathology coincident with mitochondrial pathology in control neurons. Transmission of pathology is effectively blocked using an anti-α-syn monoclonal antibody (mAb), consistent with cell-to-cell seeding of α-syn.

Potential role of ferric hemoglobin in MS pathogenesis: Effects of oxidative stress and extracellular methemoglobin or its degradation products on myelin components.

There is a well-documented relationship between cerebral vasculature and multiple sclerosis (MS) lesions: abnormal accumulations of iron have been found in the walls of the dilated veins in cerebral MS plaques. The source of this iron is unknown, but could be related to the recognized phenomenon of capillary and venous hemorrhages leading to blood extravasation. In turn, hemorrhaging leading to hemolysis results in extracellular release of hemoglobin, a reactive molecule that could induce local oxidative stress, inflammation, and tissue damage. Our previous studies with a reduced form of hemoglobin (oxyHb) have demonstrated its ability to cause extensive lipid and protein oxidation in vitro, which would result in membrane destabilization. Here, we investigated in further detail the mechanism by which the more abundant oxidized form of extracellular hemoglobin (metHb), and dissociated hemin, cause direct oxidative damage to myelin components, specifically membrane-mimetic lipid vesicles and myelin basic protein (MBP), a highly-abundant protein in the CNS. Oxidation of lipids was assessed by the formation of conjugated diene/triene and malondialdehyde, and oxidation of MBP was demonstrated by the bityrosine formation and by the change in protein mass. Our results show that metHb causes oxidative damage to MBP and myelin lipids, partly by transferring its hemin moiety to protein and lipid, but mostly as an intact protein possibly via formation of a ferryl radical. These results elucidating the mechanism of extracellular hemoglobin-induced oxidative damage to myelin components support the need for further research into vascular pathology in MS pathogenesis, to gain insight into the role of iron deposits and/or in stimulation of different comorbidities associated with the disease.

Correlation of geographic distributions of haptoglobin alleles with prevalence of multiple sclerosis (MS) - a narrative literature review.

We have proposed that the myelin damage observed in multiple sclerosis (MS) may be partly mediated through the long-term release and degradation of extracellular hemoglobin (Hb) and the products of its oxidative degradation [Cellular and Molecular Life Sciences, 71, 1789-1798, 2014]. The protein haptoglobin (Hpt) binds extracellular Hb as a first line of defense, and can serve as a vascular antioxidant. Humans have two different Hpt alleles: Hpt1 and Hpt2, giving either homozygous Hpt1-1 or Hpt2-2 phenotypes, or a heterozygous Hpt1-2 phenotype. We questioned whether those geographic regions with higher frequency of the Hpt2 allele (conversely, lower frequency of Hpt1 allele) would correlate with an increased incidence of MS, because different Hpt phenotypes will have variable anti-oxidative potentials in protecting myelin from damage inflicted by extracellular Hb and its degradation products. To test this hypothesis, we undertook a systematic analysis of the literature on reported geographic distributions of Hpt alleles to compare them with data reported in the World Health Organization Atlas of worldwide MS prevalence. We found the frequency of the Hpt1 allele to be low in European and North American countries with a high prevalence of MS, consistent with our hypothesis. However, this correlation was not observed in China and India, countries with the lowest Hpt1 frequencies, yet low reported prevalence of MS. Nevertheless, this work shows the need for continued refinement of geographic patterns of MS prevalence, including data on ethnic or racial origin, and for new clinical studies to probe the observed correlation and evaluate Hpt phenotype as a predictor of disease variability and progression, severity, and/or comorbidity with cardiovascular disorders.

Substitutions mimicking deimination and phosphorylation of 18.5-kDa myelin basic protein exert local structural effects that subtly influence its global folding.

Intrinsically-disordered proteins (IDPs) present a complex interplay of conformational variability and multifunctionality, modulated by environment and post-translational modifications. The 18.5-kDa myelin basic protein (MBP) is essential to the formation of the myelin sheath of the central nervous system and is exemplary in this regard. We have recently demonstrated that the unmodified MBP-C1 component undergoes co-operative global conformational changes in increasing concentrations of trifluoroethanol, emulating the decreasing dielectric environment that the protein encounters upon adsorption to the oligodendrocyte membrane [K.A. Vassall et al., Journal of Molecular Biology, 427, 1977-1992, 2015]. Here, we extended this study to the pseudo-deiminated MBP-C8 charge component, one found in greater proportion in developing myelin and in multiple sclerosis. A similar tri-conformational distribution as for MBP-C1 was observed with slight differences in Gibbs free energy. A more dramatic difference was observed by cathepsin D digestion of the protein in both aqueous and membrane environments, which showed significantly greater accessibility of the F42-F43 cut site of MBP-C8, indicative of a global conformational change. In contrast, this modification caused little change in the protein's density of packing on myelin-mimetic membranes as ascertained by double electron-electron resonance spectroscopy [D.R. Kattnig et al., Biochimica et Biophysica Acta (Biomembranes), 1818, 2636-2647, 2012], or in its affinity for Ca(2+)-CaM. Site-specific threonyl pseudo-phosphorylation at residues T92 and/or T95 did not appreciably affect any of the thermodynamic mechanisms of conformational transitions, susceptibility to cathepsin D, or affinity for Ca(2+)-CaM, despite previously having been shown to affect local structure and disposition on the membrane surface.

MyelStones: the executive roles of myelin basic protein in myelin assembly and destabilization in multiple sclerosis.

The classic isoforms of myelin basic protein (MBP, 14-21.5 kDa) are essential to formation of the multilamellar myelin sheath of the mammalian central nervous system (CNS). The predominant 18.5-kDa isoform links together the cytosolic surfaces of oligodendrocytes, but additionally participates in cytoskeletal turnover and membrane extension, Fyn-mediated signalling pathways, sequestration of phosphoinositides and maintenance of calcium homoeostasis. All MBP isoforms are intrinsically disordered proteins (IDPs) that interact via molecular recognition fragments (MoRFs), which thereby undergo local disorder-to-order transitions. Their conformations and associations are modulated by environment and by a dynamic barcode of post-translational modifications, particularly phosphorylation by mitogen-activated and other protein kinases and deimination [a hallmark of demyelination in multiple sclerosis (MS)]. The MBPs are thus to myelin what basic histones are to chromatin. Originally thought to be merely structural proteins forming an inert spool, histones are now known to be dynamic entities involved in epigenetic regulation and diseases such as cancer. Analogously, the MBPs are not mere adhesives of compact myelin, but active participants in oligodendrocyte proliferation and in membrane process extension and stabilization during myelinogenesis. A central segment of these proteins is pivotal in membrane-anchoring and SH3 domain (Src homology 3) interaction. We discuss in the present review advances in our understanding of conformational conversions of this classic basic protein upon membrane association, including new thermodynamic analyses of transitions into different structural ensembles and how a shift in the pattern of its post-translational modifications is associated with the pathogenesis and potentially onset of demyelination in MS.

Proton detection for signal enhancement in solid-state NMR experiments on mobile species in membrane proteins.

Direct proton detection is becoming an increasingly popular method for enhancing sensitivity in solid-state nuclear magnetic resonance spectroscopy. Generally, these experiments require extensive deuteration of the protein, fast magic angle spinning (MAS), or a combination of both. Here, we implement direct proton detection to selectively observe the mobile entities in fully-protonated membrane proteins at moderate MAS frequencies. We demonstrate this method on two proteins that exhibit different motional regimes. Myelin basic protein is an intrinsically-disordered, peripherally membrane-associated protein that is highly flexible, whereas Anabaena sensory rhodopsin is composed of seven rigid transmembrane α-helices connected by mobile loop regions. In both cases, we observe narrow proton linewidths and, on average, a 10× increase in sensitivity in 2D insensitive nuclear enhancement of polarization transfer-based HSQC experiments when proton detection is compared to carbon detection. We further show that our proton-detected experiments can be easily extended to three dimensions and used to build complete amino acid systems, including sidechain protons, and obtain inter-residue correlations. Additionally, we detect signals which do not correspond to amino acids, but rather to lipids and/or carbohydrates which interact strongly with membrane proteins.

Myelin basic protein is a glial microtubule-associated protein -- characterization of binding domains, kinetics of polymerization, and regulation by phosphorylation and a lipidic environment.

The 18.5-kDa splice isoform of myelin basic protein (MBP) predominates in the adult brain, adhering the cytoplasmic leaflets of the oligodendrocyte membrane together, but also assembling the cytoskeleton at leading edges of membrane processes. Here, we characterized MBP's role as a microtubule-assembly protein (MAP). Using light scattering and sedimentation assays we found that pseudo-phosphorylation of Ser54 (murine 18.5-kDa sequence) significantly enhanced the rate but not the final degree of polymerization. This residue lies within a short KPGSG motif identical to one in tau, a ubiquitous MAP important in neuronal microtubule assembly. Using polypeptide constructs, each comprising one of three major amphipathic α-helical molecular recognition fragments of 18.5-kDa MBP, we identified the N-terminal α1-peptide as sufficient to cause microtubule polymerization, the rate of which was significantly enhanced in the presence of dodecylphosphocholine (DPC) micelles to mimic a lipidic environment.

Thermodynamic analysis of the disorder-to-α-helical transition of 18.5-kDa myelin basic protein reveals an equilibrium intermediate representing the most compact conformation.

The intrinsically disordered, 18.5-kDa isoform of myelin basic protein (MBP) is a peripheral membrane protein that is essential to proper myelin formation in the central nervous system. MBP acts in oligodendrocytes both to adjoin membrane leaflets to each other in forming myelin and as a hub in numerous protein-protein and protein-membrane interaction networks. Like many intrinsically disordered proteins (IDPs), MBP multifunctionality arises from its high conformational plasticity and its ability to undergo reversible disorder-to-order transitions. One such transition is the disorder-to-α-helical conformational change that is induced upon MBP-membrane binding. Here, we have investigated the disorder-to-α-helical transition of MBP-derived α-peptides and the full-length 18.5-kDa protein. This transition was induced through titration of the membrane-mimetic solvent trifluoroethanol into both protein and peptide solutions, and conformational change was monitored using circular dichroism spectroscopy, 1-anilinonaphthalene-8-sulfonic acid binding, tryptophan fluorescence quenching, and Förster (fluorescence) resonance energy transfer measurements. The data suggest that the disorder-to-α-helical transition of MBP follows a 3-state model: disordered↔intermediate↔α-helical, with each of the identified equilibrium states likely representing a conformational ensemble. The disordered state is characterized by slight compaction with little regular secondary structure, whereas the intermediate is also disordered but globally more compact. Surprisingly, the α-helical conformation is less compact than the intermediate. This study suggests that multifunctionality in MBP could arise from differences in the population of energetically distinct ensembles under different conditions and also provides an example of an IDP that undergoes cooperative global conformation change.

In vitro study of the direct effect of extracellular hemoglobin on myelin components.

There is a relationship between cerebral vasculature and multiple sclerosis (MS) lesions: abnormal accumulations of iron have been found in the walls of dilated veins in MS plaques. The sources of this iron can be varied, but capillary and venous hemorrhages leading to blood extravasation have been recorded, and could result in the release of hemoglobin extracellularly. Extracellular hemoglobin oxidizes quickly and is known to become a reactive molecule that triggers low-density lipoprotein oxidation and plays a pivotal role in atherogenesis. In MS, it could lead to local oxidative stress, inflammation, and tissue damage. Here, we investigated whether extracellular hemoglobin and its breakdown products can cause direct oxidative damage to myelin components in a peroxidative environment such as occurs in inflamed tissue. Oxidation of lipids was assessed by the formation of fluorescent peroxidized lipid-protein covalent adducts, by the increase in conjugated diene and malondialdehyde. Oxidation of proteins was analyzed by the change in protein mass. The results suggest that the globin radical could be a trigger of myelin basic protein oxidative cross-linking, and that heme transferred to the lipids is involved in lipid peroxidation. This study provides new insight into the mechanism by which hemoglobin exerts its pathological oxidative activity towards myelin components. This work supports further research into the vascular pathology in MS, to gain insight into the origin and role of iron deposits in disease pathogenesis, or in stimulation of different comorbidities such as cardiovascular disease.

The proline-rich region of 18.5 kDa myelin basic protein binds to the SH3-domain of Fyn tyrosine kinase with the aid of an upstream segment to form a dynamic complex in vitro.

The intrinsically disordered 18.5 kDa classic isoform of MBP (myelin basic protein) interacts with Fyn kinase during oligodendrocyte development and myelination. It does so primarily via a central proline-rich SH3 (Src homology 3) ligand (T92-R104, murine 18.5 kDa MBP sequence numbering) that is part of a molecular switch due to its high degree of conservation and modification by MAP (mitogen-activated protein) and other kinases, especially at residues T92 and T95. Here, we show using co-transfection experiments of an early developmental oligodendroglial cell line (N19) that an MBP segment upstream of the primary ligand is involved in MBP-Fyn-SH3 association in cellula. Using solution NMR spectroscopy in vitro, we define this segment to comprise MBP residues (T62-L68), and demonstrate further that residues (V83-P93) are the predominant SH3-target, assessed by the degree of chemical shift change upon titration. We show by chemical shift index analysis that there is no formation of local poly-proline type II structure in the proline-rich segment upon binding, and by NOE (nuclear Overhauser effect) and relaxation measurements that MBP remains dynamic even while complexed with Fyn-SH3. The association is a new example first of a non-canonical SH3-domain interaction and second of a fuzzy MBP complex.

Over-expression in E. coli and purification of functional full-length murine small C-terminal domain phosphatase (SCP1, or Golli-interacting protein).

During myelination in the central nervous system, proteins arising from the gene in the oligodendrocyte lineage (golli) participate in diverse events in signal transduction and gene regulation. One of the interacting partners of the Golli-isoform BG21 was discovered by yeast-2-hybrid means and was denoted the Golli-interacting-protein (GIP). In subsequent in vitro studies of recombinant murine GIP, it was not possible to produce a full-length version of recombinant murine rmGIP in functional form under native conditions, primarily because of solubility issues, necessitating the study of a hexahistidine-tagged, truncated form ΔN-rmGIP. This protein is an acidic phosphatase belonging to the family of RNA-polymerase-2, small-subunit, C-terminal phosphatases (SCP1), and studies of the human ortholog hSCP1 have also been performed on truncated forms. Here, a new SUMO-expression and purification protocol has been developed for the preparation of a functional, full-length mSCP1/GIP (our nomenclature henceforth), with no additional purification tags. Both full-length mSCP1/GIP and the truncated murine form (now denoted ΔN-rmSCP1/GIP) had similar melting temperatures, indicating that the integrity of the catalytic core per se was minimally affected by the N-terminus. Characterization of mSCP1/GIP activity with the artificial substrate p-NPP (p-nitrophenylphosphate) yielded kinetic parameters comparable to those of ΔN-rmSCP1/GIP and the truncated human ortholog ΔN-hSCP1. Similarly, mSCP1/GIP dephosphorylated a more natural CTD-peptide substrate (but not protein kinase C-phosphorylated BG21) with comparable kinetics to ΔN-hSCP1. The successful production of an active, full-length mSCP1/GIP will enable future evaluation of the functional role of its N-terminus in protein-protein interactions (e.g., BG21) that regulate its phosphatase activity.

Regulatory effect of the glial Golli-BG21 protein on the full-length murine small C-terminal domain phosphatase (SCP1, or Golli-interacting protein).

The gene in the oligodendrocyte lineage (golli) encodes a number of proteins essential for myelination, comprising Golli and classic isoforms that are expressed in a developmentally-regulated manner. The Golli-interacting-protein (GIP) was previously discovered in a search for potential interacting partners of the Golli-isoform BG21, and was realised to be an acidic phosphatase belonging to the family of RNA-polymerase-2, small-subunit, C-terminal phosphatases (viz., SCP1). Here, we refer to this protein as mSCP1/GIP. In subsequent in vitro studies of recombinant murine SCP1/GIP, the inability to produce an active full-length version of the protein under native conditions necessitated the study of a truncated form ΔN-rmSCP1/GIP, but with inconclusive results regarding its interaction with BG21 [13]. We have since developed a new SUMO-expression and purification protocol for the preparation of a functional, full-length mGIP/SCP1, with no additional purification tags. Here, the interaction between mSCP1/GIP (with intact N-terminus) and BG21 is shown to be different than for the truncation mutant studied previously. Specifically, this interaction shows a dual effect on the enzymatic activity of mSCP1/GIP by BG21: BG21 enhanced mSCP1/GIP phosphatase activity (Ka = 30 µM), whereas PKCα-phosphorylated BG21 inhibited its activity (Ki = 2.9 µM), suggesting a potential role of BG21 as a molecular switch ("quick-brake mechanism") on mSCP1/GIP. The successful production of an active, full-length mSCP1/GIP thus demonstrates a role for its N-terminus in regulation of phosphatase activity, in events such as the regulation of transcription in oligodendrocytes.

Hemoglobin as a source of iron overload in multiple sclerosis: does multiple sclerosis share risk factors with vascular disorders?

Although iron is known to be essential for the normal development and health of the central nervous system, abnormal iron deposits are found in and around multiple sclerosis (MS) lesions that themselves are closely associated with the cerebral vasculature. However, the origin of this excess iron is unknown, and it is not clear whether this is one of the primary causative events in the pathogenesis of MS, or simply another consequence of the long-lasting inflammatory conditions. Here, applying a systems biology approach, we propose an additional way for understanding the neurodegenerative component of the disease caused by chronic subclinical extravasation of hemoglobin, in combination with multiple other factors including, but not limited to, dysfunction of different cellular protective mechanisms against extracellular hemoglobin reactivity and oxidative stress. Moreover, such considerations could also shed light on and explain the higher susceptibility of MS patients to a wide range of cardiovascular disorders.

Solution nuclear magnetic resonance structure and molecular dynamics simulations of a murine 18.5 kDa myelin basic protein segment (S72-S107) in association with dodecylphosphocholine micelles.

The 18.5 kDa myelin basic protein (MBP), the most abundant splice isoform in adult mammalian myelin, is a multifunctional, intrinsically disordered protein involved in the development and compaction of the myelin sheath in the central nervous system. A highly conserved central segment comprises a membrane-anchoring amphipathic α-helix followed by a proline-rich segment that represents a ligand for SH3 domain-containing proteins. Here, we have determined using solution nuclear magnetic resonance spectroscopy the structure of a 36-residue peptide fragment of MBP (murine 18.5 kDa residues S72-S107, denoted the α2-peptide) comprising these two structural motifs, in association with dodecylphosphocholine (DPC) micelles. The structure was calculated using CS-ROSETTA (version 1.01) because the nuclear Overhauser effect restraints were insufficient for this protein. The experimental studies were complemented by molecular dynamics simulations of a corresponding 24-residue peptide fragment (murine 18.5 kDa residues E80-G103, denoted the MD-peptide), also in association with a DPC micelle in silico. The experimental and theoretical results agreed well with one another, despite the independence of the starting structures and analyses, both showing membrane association via the amphipathic α-helix, and a sharp bend in the vicinity of the Pro93 residue (murine 18.5 kDa sequence numbering). Overall, the conformations elucidated here show how the SH3 ligand is presented to the cytoplasm for interaction with SH3 domain-containing proteins such as Fyn and contribute to our understanding of myelin architecture at the molecular level.