Mutations in GDAP1 Influence Structure and Function of the Trans-Golgi Network

Charcot-Marie-Tooth disease (CMT) is a heritable neurodegenerative disease that displays great genetic heterogeneity. The genes and mutations that underlie this heterogeneity have been extensively characterized by molecular genetics. However, the molecular pathogenesis of the vast majority of CMT subtypes remains terra incognita. Any attempts to perform experimental therapy for CMT disease are limited by a lack of understanding of the pathogenesis at a molecular level. In this study, we aim to identify the molecular pathways that are disturbed by mutations in the gene encoding GDAP1 using both yeast and human cell, based models of CMT-GDAP1 disease. We found that some mutations in GDAP1 led to a reduced expression of the GDAP1 protein and resulted in a selective disruption of the Golgi apparatus. These structural alterations are accompanied by functional disturbances within the Golgi. We screened over 1500 drugs that are available on the market using our yeast-based CMT-GDAP1 model. Drugs were identified that had both positive and negative effects on cell phenotypes. To the best of our knowledge, this study is the first report of the Golgi apparatus playing a role in the pathology of CMT disorders. The drugs we identified, using our yeast-based CMT-GDAP1 model, may be further used in translational research

Interaction of prion protein with microtubules

Nieprawidłowo sfałdowane białko prionowe (PrPTSE) uważane jest za główny czynnik prowadzący do rozwoju zakaźnych chorób neurodegeneracyjnych, zwanych pasażowalnymi encefalopatiami gąbczastymi (TSE). Mechanizm konwersji fizjologicznej formy białka prionowego PrPC do patologicznej PrPTSE, jak i forma neurotoksyczna tego białka, nie zostały jak dotąd w pełni scharakteryzowane. W warunkach fizjologicznych PrPc występuje głównie zewnątrzkomórkowo, gdzie przyczepione jest za pomocą kotwicy GPI do powierzchni błony komórkowej. Znane są jednak, również zlokalizowane w cytoplazmie formy PrP, zwane cytoPrP. Co ciekawe, stężenie cytoPrP znacząco wzrasta w TSE. Badania ostatnich lat dowodzą, że nieprawidłowo zlokalizowane w cytoplazmie PrP może być czynnikiem neurotoksycznym, a mechanizm neurotoksyczności związany jest prawdopodobnie z bezpośrednim oddziaływaniem tej formy białka prionowego z tubuliną. Oddziaływanie to prowadzi do agregacji tubuliny, zahamowania formowania MT, rozpadu cytoszkieletu mikrotubularnego i w konsekwencji śmierci komórki. Stabilizacja MT, np. przez obniżenie poziomu ufosforylowania związanych z mikrotubulami białek MAP chroni neurony przed toksycznością cytoplazmatycznej formy PrP.Misfolded prion protein (PrP ) is known as a major agent leading to infectious neurodegenerative diseases, known as transmissible spongiform encephalopathies (TSE). The mechanism of conversion of the physiological form of prion protein (PrP C ) into the pathological PrP TSE as well as the identity of neurotoxic form of this protein is not fully characterized. Under physiological conditions, PrP C one, is predominantly extracellular, tethered to the plasma membrane surface through the GPI anchor. However, cytosolic forms of PrP, termed as cytoPrP have also been found. Interestingly, a significant increase in the concentration of cytoPrP is observed in TSE. Recently, it was shown that mislocalized PrP can be a neurotoxic agent. The mechanism of neurotoxicity might be linked to the direct interaction of this form of PrP with tubulin. This interaction leads to tubulin aggregation, inhibition of microtubules (MT) assembly, disruption of microtubular cytoskeleton and eventually cell death. MT stabilization, by decreasing the level of MAP phosphorylation, can protect neurons from toxic effect of cytosolic forms of PrP

The effects of the interaction of myosin essential light chain isoforms with actin in skeletal muscles.

In order to compare the ability of different isoforms of myosin essential light chain to interact with actin, the effect of the latter protein on the proteolytic susceptibility of myosin light chains (MLC-1S and MLC-1V - slow specific and same as ventricular isoform) from slow skeletal muscle was examined. Actin protects both slow muscle essential light chain isoforms from papain digestion, similarly as observed for fast skeletal muscle myosin (Nieznańska et al., 1998, Biochim. Biophys. Acta 1383: 71). The effect of actin decreases as ionic strength rises above physiological values for both fast and slow skeletal myosin, confirming the ionic character of the actin-essential light chain interaction. To better understand the role of this interaction, we examined the effect of synthetic peptides spanning the 10-amino-acid N-terminal sequences of myosin light chain 1 from fast skeletal muscle (MLC-1F) (MLCFpep: KKDVKKPAAA), MLC-1S (MLCSpep: KKDVPVKKPA) and MLC-1V (MLCVpep: KPEPKKDDAK) on the myofibrillar ATPase of fast and slow skeletal muscle. In the presence of MLCFpep, we observed an about 19% increase, and in the presence of MLCSpep about 36% increase, in the myofibrillar ATPase activity of fast muscle. On the other hand, in myofibrillar preparations from slow skeletal muscle, MLCSpep as well as MLCVpep caused a lowering of the ATPase activity by about 36%. The above results suggest that MLCSpep induces opposite effects on ATPase activity, depending on the type of myofibrils, but not through its specific N-terminal sequence - which differs from other MLC N-terminal peptides. Our observations lead to the conclusion that the action of different isoforms of long essential light chain is similar in slow and fast skeletal muscle. However the interaction of essential light chains with actin leads to different physiological effects probably depending on the isoforms of other myofibrillar proteins

Covalent defects restrict supramolecular self-assembly of homopolypeptides: case study of β2-fibrils of poly-L-glutamic acid.

Poly-L-glutamic acid (PLGA) often serves as a model in studies on amyloid fibrils and conformational transitions in proteins, and as a precursor for synthetic biomaterials. Aggregation of PLGA chains and formation of amyloid-like fibrils was shown to continue on higher levels of superstructural self-assembly coinciding with the appearance of so-called β2-sheet conformation manifesting in dramatic redshift of infrared amide I' band below 1600 cm(-1). This spectral hallmark has been attributed to network of bifurcated hydrogen bonds coupling C = O and N-D (N-H) groups of the main chains to glutamate side chains. However, other authors reported that, under essentially identical conditions, PLGA forms the conventional in terms of infrared characteristics β1-sheet structure (exciton-split amide I' band with peaks at ca. 1616 and 1683 cm(-1)). Here we attempt to shed light on this discrepancy by studying the effect of increasing concentration of intentionally induced defects in PLGA on the tendency to form β1/β2-type aggregates using infrared spectroscopy. We have employed carbodiimide-mediated covalent modification of Glu side chains with n-butylamine (NBA), as well as electrostatics-driven inclusion of polylysine chains, as two different ways to trigger structural defects in PLGA. Our study depicts a clear correlation between concentration of defects in PLGA and increasing tendency to depart from the β2-structure toward the one less demanding in terms of chemical uniformity of side chains: β1-structure. The varying predisposition to form β1- or β2-type aggregates assessed by infrared absorption was compared with the degree of morphological order observed in electron microscopy images. Our results are discussed in the context of latent covalent defects in homopolypeptides (especially with side chains capable of hydrogen-bonding) that could obscure their actual propensities to adopt different conformations, and limit applications in the field of synthetic biomaterials

Covalent Defects Restrict Supramolecular Self-Assembly of Homopolypeptides: Case Study of β₂-Fibrils of Poly-L-Glutamic Acid

<div><p>Poly-L-glutamic acid (PLGA) often serves as a model in studies on amyloid fibrils and conformational transitions in proteins, and as a precursor for synthetic biomaterials. Aggregation of PLGA chains and formation of amyloid-like fibrils was shown to continue on higher levels of superstructural self-assembly coinciding with the appearance of so-called β₂-sheet conformation manifesting in dramatic redshift of infrared amide I′ band below 1600 cm⁻¹. This spectral hallmark has been attributed to network of bifurcated hydrogen bonds coupling C = O and N-D (N-H) groups of the main chains to glutamate side chains. However, other authors reported that, under essentially identical conditions, PLGA forms the conventional in terms of infrared characteristics β₁-sheet structure (exciton-split amide I′ band with peaks at ca. 1616 and 1683 cm⁻¹). Here we attempt to shed light on this discrepancy by studying the effect of increasing concentration of intentionally induced defects in PLGA on the tendency to form β₁/β₂-type aggregates using infrared spectroscopy. We have employed carbodiimide-mediated covalent modification of Glu side chains with n-butylamine (NBA), as well as electrostatics-driven inclusion of polylysine chains, as two different ways to trigger structural defects in PLGA. Our study depicts a clear correlation between concentration of defects in PLGA and increasing tendency to depart from the β₂-structure toward the one less demanding in terms of chemical uniformity of side chains: β₁-structure. The varying predisposition to form β₁- or β₂-type aggregates assessed by infrared absorption was compared with the degree of morphological order observed in electron microscopy images. Our results are discussed in the context of latent covalent defects in homopolypeptides (especially with side chains capable of hydrogen-bonding) that could obscure their actual propensities to adopt different conformations, and limit applications in the field of synthetic biomaterials.</p></div

Cross-section view at a model of different inter-sheet distances and packing modes of Glu side chains in the β₁/β₂-type structural variants of PLGA aggregates with the antiparallel arrangement of strands (A).

<p>Red circles mark sites of three-center hydrogen bonds with bifurcated carbonyl acceptors. Random covalent modification of Glu side chains (within frames) cause local structural defects and result in less-densely-packed β₁ fibrils (B).</p

Infrared spectra of PLGA aggregates doped with PLL (black lines), or PDL (red lines) at the indicated Glu:Lys side chain molar ratios.

<p>Aggregates were formed by incubation (72h/60°C) of acidified mixtures of PLGA and PLL (PDL). Blue spectrum corresponds to β₂-fibrils formed in the absence of polylysine.</p

Spectral characteristics of NBA/EDC-modified PLGA samples.

<p>Far-UV CD spectra of PLGA samples modified with NBA (at fixed1∶3 Glu side chain: NBA molar ratio) in the presence of varying concentrations of EDC (expressed as molar ratio of EDC:Glu side chains: 0, 0.005, 0.015, 0.05, 0.15, 0.5, and 1.5) after alkalization to pH 8.3 (A) and subsequent acidification to pH 4.9 (B). Changes in light scattering intensity (at 350 nm) of NBA/EDC-modified PLGA formed at 1.5 EDC:Glu molar ratio caused by pH-adjustment are shown in the inset in panel (B).</p

TEM (top row) and SEM (bottom row) images of amyloid fibrils formed by unmodified PLGA (β₂) and selected NBA/EDC-modified PLGA samples.

<p>TEM (top row) and SEM (bottom row) images of amyloid fibrils formed by unmodified PLGA (β₂) and selected NBA/EDC-modified PLGA samples.</p

On the Heat Stability of Amyloid-Based Biological Activity: Insights from Thermal Degradation of Insulin Fibrils

<div><p>Formation of amyloid fibrils in vivo has been linked to disorders such as Alzheimer’s disease and prion-associated transmissible spongiform encephalopathies. One of the characteristic features of amyloid fibrils is the high thermodynamic stability relative both to native and disordered states which is also thought to underlie the perplexingly remarkable heat resistance of prion infectivity. Here, we are comparing high-temperature degradation of native and fibrillar forms of human insulin. Decomposition of insulin amyloid has been studied under helium atmosphere and in the temperature range from ambient conditions to 750°C using thermogravimetry and differential scanning calorimetry coupled to mass spectrometry. While converting native insulin into amyloid does upshift onset of thermal decomposition by ca. 75°C, fibrils remain vulnerable to covalent degradation at temperatures below 300°C, as reflected by mass spectra of gases released upon heating of amyloid samples, as well as morphology and infrared spectra of fibrils subjected to incubation at 250°C. Mass spectra profiles of released gases indicate that degradation of fibrils is much more cooperative than degradation of native insulin. The data show no evidence of water of crystallization trapped within insulin fibrils. We have also compared untreated and heated amyloid samples in terms of capacity to seed daughter fibrils. Kinetic traces of seed-induced insulin fibrillation have shown that the seeding potency of amyloid samples decreases significantly already after exposure to 200°C, even though corresponding electron micrographs indicated persisting fibrillar morphology. Our results suggest that amyloid-based biological activity may not survive extremely high temperature treatments, at least in the absence of other stabilizing factors.</p></div