Determination of the Sites of Posttranslational Modifications in the Charge Isomers of Bovine Myelin Basic Protein by Capillary Electrophoresis-Mass Spectroscopy

Zand, Ramin; Li, Michael X.; Jin, Xiaoying; Lubman, David M.

doi:10.1021/bi972347t

Cited by 62 publications

(58 citation statements)

References 35 publications

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“…These result from deamidation, phosphorylation, C-terminal arginine loss, and the deimination of arginyl residues (70). In many cases, these post-translational modifications are thought to regulate myelin assembly, MBP-ligand interactions, and signaling functions (71). MBP interacts with many different ligands, including lipids (69,72), calmodulin (73), divalent cations (74), GTP (75), and cytoskeletal proteins such as tubulin (76) and actin (77).…”

Section: Discussionmentioning

confidence: 99%

Inhibition of Familial Cerebral Amyloid Angiopathy Mutant Amyloid β-Protein Fibril Assembly by Myelin Basic Protein

Hoos

Ahmed

Smith

et al. 2007

Journal of Biological Chemistry

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Deposition of fibrillar amyloid ␤-protein (A␤) in the brain is a prominent pathological feature of Alzheimer disease and related disorders, including familial forms of cerebral amyloid angiopathy (CAA). Mutant forms of A␤, including Dutch-and Iowa-type A␤, which are responsible for familial CAA, deposit primarily as fibrillar amyloid along the cerebral vasculature and are either absent or present only as diffuse non-fibrillar plaques in the brain parenchyma. Despite the lack of parenchymal fibril formation in vivo, these CAA mutant A␤ peptides exhibit a markedly increased rate and extent of fibril formation in vitro compared with wild-type A␤. Based on these conflicting observations, we sought to determine whether brain parenchymal factors that selectively interact with and modulate CAA mutant A␤ fibril assembly exist. Using a combination of immunoaffinity chromatography and mass spectrometry, we identified myelin basic protein (MBP) as a prominent brain parenchymal factor that preferentially binds to CAA mutant A␤ compared with wild-type A␤. Surface plasmon resonance measurements confirmed that MBP bound more tightly to Dutch/Iowa CAA double mutant A␤ than to wild-type A␤. Using a combination of biochemical and ultrastructural techniques, we found that MBP inhibited the fibril assembly of CAA mutant A␤. Together, these findings suggest a possible role for MBP in regulating parenchymal fibrillar A␤ deposition in familial CAA. Extracellular deposition of amyloid ␤-protein (A␤)2 in the brain is a prominent feature of Alzheimer disease and other related disorders (1). A␤ is a 39 -43-amino acid peptide that exhibits a high propensity to self-assemble into ␤-sheet-containing oligomeric forms and fibrils (2). A␤ peptides are proteolytically produced from the amyloid ␤-protein precursor (A␤PP), a large type I integral membrane protein, through sequential proteolysis by ␤-and ␥-secretase activities (3-6). Cerebral deposition of A␤ in the parenchyma can occur as diffuse plaques, with little surrounding pathology, or as fibrillar plaques associated with dystrophic neurons, neurofibrillary tangles, and inflammation (1). Fibrillar A␤ deposition also occurs within and along primarily small and medium arteries and arterioles of the cerebral cortex and leptomeninges and in the cerebral microvasculature, a condition known as cerebral amyloid angiopathy (CAA) (7-9). This condition accounts for up to 20% of all spontaneous primary intracerebral hemorrhages and is a key pathological lesion in nearly all patients with Alzheimer disease and certain related disorders. Accumulation of fibrillar cerebral vascular A␤ has been shown to cause degeneration and cell death of smooth muscle cells and pericytes in affected larger cerebral vessels and cerebral microvessels, respectively (9 -11). Recent findings have implicated cerebral microvascular A␤ deposition in promoting neuroinflammation and dementia in Alzheimer disease (12-15).There exist several familial monogenic forms of CAA resulting from specific point mutations within the A␤ seque...

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Section: Discussionmentioning

confidence: 99%

Inhibition of Familial Cerebral Amyloid Angiopathy Mutant Amyloid β-Protein Fibril Assembly by Myelin Basic Protein

Hoos

Ahmed

Smith

et al. 2007

Journal of Biological Chemistry

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“…Whereas an assessment of the post-translational modifications in the "charge isomers" of MBP from bovine and dogfish have been reported (21,22), no similar analysis has been carried out for the human MBP "charge isomers." As a first step in defining the roles of these three major modifications, we have isolated several of the MBP charge isomers, protease digested each, resolved the peptides by liquid chromatography, and identified the modification(s) in each by mass spectrometry.…”

Section: Multiple Sclerosis (Ms)mentioning

confidence: 99%

Multiple Sclerosis

Kim

Mastronardi

Wood

et al. 2003

Molecular & Cellular Proteomics

178

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Myelin basic protein (MBP) represents a candidate autoantigen in multiple sclerosis (MS). We isolated MBP from normal and MS human white matter and purified six components (charge isomers) to compare the post-translational modifications on each. The sites and extent of methylation, deimination, and phosphorylation were documented for all tryptic peptides by mass spectrometry. We found that mono and dimethylated arginine 107 was increased in MS samples; deimination of arginine occurred at a number of sites and was elevated in MS; phosphorylation was observed in 10 peptides in normal samples but was greatly reduced or absent in most peptides from MS samples. Data obtained with MBP isolated from fresh brain obtained from a spontaneously demyelinating mouse model supported the view that the changes observed in human brain were probably related to pathogenesis of demyelination, i.e. we found decreased phosphorylation and decreased amounts of glycogen synthesis kinase in brain homogenates using specific antibodies. This study represents the first to define post-translational modifications in demyelinating disease and suggest an important role in pathogenesis. Molecular & Cellular Proteomics 2:453-462, 2003. Multiple sclerosis (MS)1 is the most common demyelinating disease of the human central nervous system. It is multifactorial, requiring genetic, environmental (possibly viral), and immunological factors (1). Genetic screens of MS populations have failed to uncover a major susceptibility locus (2), suggesting that MS is a polygenic disease with each gene of small effect.Myelin basic protein (MBP), a major myelin protein that accounts for 35% of the total myelin protein, is a strong candidate autoantigen (3). It is a 170-amino acid protein in the human, containing 19 arginyl and 12 lysyl residues, which accounts for its basic character. It is devoid of cysteinyl residues, with a high proportion of disorder promoting amino acids such as A, R, G, Q, S, P, E, and K. It is a member of an expanding group of proteins that include the amyloid and prion proteins, considered to be intrinsically disordered (4), in which the disordered state is the functional state. Because of this, post-translational modifications determine the nature and extent of secondary structure, permitting the protein to adopt multiple conformations for a variety of binding events (5). Because interactions between the positive arginyl and lysyl residues and the negatively charged phosphate groups of the membrane phospholipids are essential to the structure of compact myelin, changes in positive charge of MBP would decrease the strength of these interactions (6).MBP is an unusual protein that has never been crystallized due to the myriad of post-translational modifications it possesses. These include phosphorylation, deamidation, deimination, arginine methylation, and N-terminal acylation. These give rise to a family of microheteromers or "charge isomers," several of which can be resolved by chromatography (7). The effects of some of these modifications o...

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“…In addition to the different molecular mass species, at least eight charge isoforms have been shown to exist for the prominent adult 18.5-kDa protein. These numerous post-translational modifications in many cases are thought to regulate myelin assembly, MBP-ligand interactions, and signaling functions (24). It is not known whether post-translational modifications are required for the ability of MBP to bind A␤ and inhibit its fibrillar assembly or what region of the MBP protein is responsible for this activity.…”

mentioning

confidence: 99%

N-terminal Domain of Myelin Basic Protein Inhibits Amyloid β-Protein Fibril Assembly

Liao

Hoos

Aucoin

et al. 2010

Journal of Biological Chemistry

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In the present study, we demonstrate that human MBP purified from either brain or a bacterial recombinant expression system comparably bound to A␤ and inhibited A␤ fibril assembly indicating that post-translational modifications are not required for this activity. We also show that purified mouse brain MBP and recombinantly expressed mouse MBP similarly inhibited A␤ fibril formation. Through a combination of biochemical and ultrastructural techniques, we demonstrate that the binding site for A␤ is located in the N-terminal 64 amino acids of MBP and that a stable peptide (MBP1) comprising these residues was sufficient to inhibit A␤ fibrillogenesis. Under conditions comparable with those used for A␤, the fibrillar assembly of amylin, another amyloidogenic peptide, was not inhibited by MBP1, although MBP1 still bound to it. This observation suggests that the potent inhibitory effect of MBP on fibril formation is not general to amyloidogenic peptides. Finally, MBP1 could prevent the cytotoxic effects of A␤ in primary cortical neurons. Our findings suggest that inhibition of A␤ fibril assembly by MBP, mediated through its N-terminal domain, could play a role in influencing amyloid formation in Alzheimer disease brain and corresponding mouse models. The histopathology of Alzheimer disease (AD)2 is characterized by the prominent presence of plaques of amyloid ␤-protein (A␤) in the brain parenchyma (1). Dystrophic neurons and neuronal loss are often associated with A␤ accumulation leading to the clinical manifestation of cognitive decline and memory loss. A␤ is derived from the amyloid ␤-protein precursor (A␤PP) through sequential proteolysis by ␤-and ␥-secretases yielding peptides of between 39 and 43 residues (2-5). These peptides exhibit a high propensity to self-assemble into ␤-sheet-containing oligomers and fibrils of which the oligomeric forms are widely believed to be the most toxic species of the peptide, responsible for the majority of neuronal loss (6). A condition known as cerebral amyloid angiopathy (CAA) is prevalently found in AD and is characterized by fibrillar deposition of A␤ along arteries and arterioles of the cerebral cortex, leptomeninges, and cerebral microvasculature (6 -8). Apart from the more typical CAA, which commonly occurs in AD, familial forms of CAA exist that are the result of specific point mutations within the A␤ sequence of the A␤PP gene (9 -15). Two well studied examples of familial CAA are Dutch type, resulting from an E22Q substitution in A␤ (9, 10), and Iowa type, resulting from a D23N substitution in A␤ (15).Elucidating the molecules and processes in brain that regulate A␤ assembly and accumulation as parenchymal plaques and cerebral vascular deposits is important for understanding the pathogenesis of AD and related disorders as well as for providing opportunities for development of potential therapeutic interventions. Previously, we found that myelin basic protein (MBP) strongly bound to a highly fibrillogenic A␤40 peptide that contains both the Dutch and Iowa mutations (A␤40DI)...

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Determination of the Sites of Posttranslational Modifications in the Charge Isomers of Bovine Myelin Basic Protein by Capillary Electrophoresis-Mass Spectroscopy

Cited by 62 publications

References 35 publications

Inhibition of Familial Cerebral Amyloid Angiopathy Mutant Amyloid β-Protein Fibril Assembly by Myelin Basic Protein

Inhibition of Familial Cerebral Amyloid Angiopathy Mutant Amyloid β-Protein Fibril Assembly by Myelin Basic Protein

Multiple Sclerosis

N-terminal Domain of Myelin Basic Protein Inhibits Amyloid β-Protein Fibril Assembly

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