Molecular mechanisms in chloroquine-exposed muscle cells elucidated by combined proteomic and microscopic studies

OBJECTIVES

Chloroquine (CQ) is an antimalarial drug with a growing number of applications as recently demonstrated in attempts to treat Covid-19. For decades, it has been well known that skeletal and cardiac muscle cells might display vulnerability against CQ exposure resulting in the clinical manifestation of a CQ-induced myopathy. In line with the known effect of CQ on inhibition of the lysosomal function and thus cellular protein clearance, the build-up of autophagic vacuoles along with protein aggregates is a histological hallmark of the disease. Given that protein targets of the perturbed proteostasis are still not fully discovered, we applied different proteomic and immunological-based studies to improve the current understanding of the biochemical nature of CQ-myopathy.

METHODS

To gain a comprehensive understanding of the molecular pathogenesis of this acquired myopathy and to define proteins targets as well as pathophysiological processes beyond impaired proteolysis, utilising CQ-treated C2C12 cells and muscle biopsies derived from CQ-myopathy patients, we performed different proteomic approaches and Coherent Anti-Stokes Raman Scattering (CARS) microscopy, in addition to immunohistochemical studies.

RESULTS

Our combined studies confirmed an impact of CQ-exposure on proper protein processing/folding and clearance, highlighted changes in the interactome of p62, a known aggregation marker and hereby identified the Rett syndrome protein MeCP2 as being affected. Moreover, our approach revealed-among others-a vulnerability of the extracellular matrix, cytoskeleton and lipid homeostasis.

CONCLUSION

We demonstrated that CQ exposure (secondarily) impacts biological processes beyond lysosomal function and linked a variety of proteins with known roles in the manifestation of other neuromuscular diseases.

Non-invasive monitoring of microbial triterpenoid production using nonlinear microscopy techniques

Introduction: Bioproduction of plant-derived triterpenoids in recombinant microbes is receiving great attention to make these biologically active compounds industrially accessible as nutraceuticals, pharmaceutics, and cosmetic ingredients. So far, there is no direct method for detecting triterpenoids under physiological conditions on a cellular level, information yet highly relevant to rationalizing microbial engineering. Methods: Here, we show in a proof-of-concept study, that triterpenoids can be detected and monitored in living yeast cells by combining coherent anti-Stokes Raman scattering (CARS) and second-harmonic-generation (SHG) microscopy techniques. We applied CARS and SHG microscopy measurements, and for comparison classical Nile Red staining, on immobilized and growing triterpenoid-producing, and non-producing reference Saccharomyces cerevisiae strains. Results and Discussion: We found that the SHG signal in triterpenoid-producing strains is significantly higher than in a non-producing reference strain, correlating with lipophile content as determined by Nile red staining. In growing cultures, both CARS and SHG signals showed changes over time, enabling new insights into the dynamics of triterpenoid production and storage inside cells.

Phenotypical and Myopathological Consequences of Compound Heterozygous Missense and Nonsense Variants in SLC18A3

Background: Presynaptic forms of congenital myasthenic syndromes (CMS) due to pathogenic variants in SLC18A3 impairing the synthesis and recycling of acetylcholine (ACh) have recently been described. SLC18A3 encodes the vesicular ACh transporter (VAChT), modulating the active transport of ACh at the neuromuscular junction, and homozygous loss of VAChT leads to lethality. Methods: Exome sequencing (ES) was carried out to identify the molecular genetic cause of the disease in a 5-year-old male patient and histological, immunofluorescence as well as electron- and CARS-microscopic studies were performed to delineate the muscle pathology, which has so far only been studied in VAChT-deficient animal models. Results: ES unraveled compound heterozygous missense and nonsense variants (c.315G>A, p.Trp105* and c.1192G>C, p.Asp398His) in SLC18A3. Comparison with already-published cases suggests a more severe phenotype including impaired motor and cognitive development, possibly related to a more severe effect of the nonsense variant. Therapy with pyridostigmine was only partially effective while 3,4 diaminopyridine showed no effect. Microscopic investigation of the muscle biopsy revealed reduced fibre size and a significant accumulation of lipid droplets. Conclusions: We suggest that nonsense variants have a more detrimental impact on the clinical manifestation of SLC18A3-associated CMS. The impact of pathogenic SLC18A3 variants on muscle fibre integrity beyond the effect of denervation is suggested by the build-up of lipid aggregates. This in turn implicates the importance of proper VAChT-mediated synthesis and recycling of ACh for lipid homeostasis in muscle cells. This hypothesis is further supported by the pathological observations obtained in previously published VAChT-animal models.

Intracellular Lipid Accumulation and Mitochondrial Dysfunction Accompanies Endoplasmic Reticulum Stress Caused by Loss of the Co-chaperone DNAJC3

Recessive mutations in DNAJC3, an endoplasmic reticulum (ER)-resident BiP co-chaperone, have been identified in patients with multisystemic neurodegeneration and diabetes mellitus. To further unravel these pathomechanisms, we employed a non-biased proteomic approach and identified dysregulation of several key cellular pathways, suggesting a pathophysiological interplay of perturbed lipid metabolism, mitochondrial bioenergetics, ER-Golgi function, and amyloid-beta processing. Further functional investigations in fibroblasts of patients with DNAJC3 mutations detected cellular accumulation of lipids and an increased sensitivity to cholesterol stress, which led to activation of the unfolded protein response (UPR), alterations of the ER-Golgi machinery, and a defect of amyloid precursor protein. In line with the results of previous studies, we describe here alterations in mitochondrial morphology and function, as a major contributor to the DNAJC3 pathophysiology. Hence, we propose that the loss of DNAJC3 affects lipid/cholesterol homeostasis, leading to UPR activation, β-amyloid accumulation, and impairment of mitochondrial oxidative phosphorylation.

Coupling Miniaturized Free-Flow Electrophoresis to Mass Spectrometry via a Multi-Emitter ESI Interface

We present a novel multi-emitter electrospray ionization (ESI) interface for the coupling of microfluidic free-flow electrophoresis (μFFE) with mass spectrometry (MS). The effluents of the μFFE outlets are analyzed in near real-time, allowing a direct optimization of the electrophoretic separation and an online monitoring of qualitative sample compositions. The short measurement time of just a few seconds for all outlets even enables a reasonable time-dependent monitoring. As a proof of concept, we employ the multi-emitter ESI interface for the continuous identification of analytes at 15 μFFE outlets via MS to optimize the μFFE separation of important players of cellular respiration in operando. The results indicate great potential of the presented system in downstream processing control, for example, for the monitoring and purification of products in continuous-flow microreactors.

Protein signature of human skin fibroblasts allows the study of the molecular etiology of rare neurological diseases

BACKGROUND

The elucidation of pathomechanisms leading to the manifestation of rare (genetically caused) neurological diseases including neuromuscular diseases (NMD) represents an important step toward the understanding of the genesis of the respective disease and might help to define starting points for (new) therapeutic intervention concepts. However, these "discovery studies" are often limited by the availability of human biomaterial. Moreover, given that results of next-generation-sequencing approaches frequently result in the identification of ambiguous variants, testing of their pathogenicity is crucial but also depending on patient-derived material.

METHODS

Human skin fibroblasts were used to generate a spectral library using pH8-fractionation of followed by nano LC-MS/MS. Afterwards, Allgrove-patient derived fibroblasts were subjected to a data independent acquisition approach. In addition, proteomic signature of an enriched nuclear protein fraction was studied. Proteomic findings were confirmed by immunofluorescence in a muscle biopsy derived from the same patient and cellular lipid homeostasis in the cause of Allgrove syndrome was analysed by fluorescence (BODIPY-staining) and coherent anti-Stokes Raman scattering (CARS) microscopy.

RESULTS

To systematically address the question if human skin fibroblasts might serve as valuable biomaterial for (molecular) studies of NMD, we generated a protein library cataloguing 8280 proteins including a variety of such linked to genetic forms of motoneuron diseases, congenital myasthenic syndromes, neuropathies and muscle disorders. In silico-based pathway analyses revealed expression of a diversity of proteins involved in muscle contraction and such decisive for neuronal function and maintenance suggesting the suitability of human skin fibroblasts to study the etiology of NMD. Based on these findings, next we aimed to further demonstrate the suitability of this in vitro model to study NMD by a use case: the proteomic signature of fibroblasts derived from an Allgrove-patient was studied. Dysregulation of paradigmatic proteins could be confirmed in muscle biopsy of the patient and protein-functions could be linked to neurological symptoms known for this disease. Moreover, proteomic investigation of nuclear protein composition allowed the identification of protein-dysregulations according with structural perturbations observed in the muscle biopsy. BODIPY-staining on fibroblasts and CARS microscopy on muscle biopsy suggest altered lipid storage as part of the underlying disease etiology.

CONCLUSIONS

Our combined data reveal that human fibroblasts may serve as an in vitro system to study the molecular etiology of rare neurological diseases exemplified on Allgrove syndrome in an unbiased fashion.

Molecular pathophysiology of human MICU1 deficiency

AIMS

MICU1 encodes the gatekeeper of the mitochondrial Ca²⁺ uniporter, MICU1 and biallelic loss-of-function mutations cause a complex, neuromuscular disorder in children. Although the role of the protein is well understood, the precise molecular pathophysiology leading to this neuropaediatric phenotype has not been fully elucidated. Here we aimed to obtain novel insights into MICU1 pathophysiology.

METHODS

Molecular genetic studies along with proteomic profiling, electron-, light- and Coherent anti-Stokes Raman scattering microscopy and immuno-based studies of protein abundances and Ca²⁺ transport studies were employed to examine the pathophysiology of MICU1 deficiency in humans.

RESULTS

We describe two patients carrying MICU1 mutations, two nonsense (c.52C>T; p.(Arg18*) and c.553C>T; p.(Arg185*)) and an intragenic exon 2-deletion presenting with ataxia, developmental delay and early onset myopathy, clinodactyly, attention deficits, insomnia and impaired cognitive pain perception. Muscle biopsies revealed signs of dystrophy and neurogenic atrophy, severe mitochondrial perturbations, altered Golgi structure, vacuoles and altered lipid homeostasis. Comparative mitochondrial Ca²⁺ transport and proteomic studies on lymphoblastoid cells revealed that the [Ca²⁺ ] threshold and the cooperative activation of mitochondrial Ca²⁺ uptake were lost in MICU1-deficient cells and that 39 proteins were altered in abundance. Several of those proteins are linked to mitochondrial dysfunction and/or perturbed Ca²⁺ homeostasis, also impacting on regular cytoskeleton (affecting Spectrin) and Golgi architecture, as well as cellular survival mechanisms.

CONCLUSIONS

Our findings (i) link dysregulation of mitochondrial Ca²⁺ uptake with muscle pathology (including perturbed lipid homeostasis and ER-Golgi morphology), (ii) support the concept of a functional interplay of ER-Golgi and mitochondria in lipid homeostasis and (iii) reveal the vulnerability of the cellular proteome as part of the MICU1-related pathophysiology.

Multiplexed Online Monitoring of Microfluidic Free-Flow Electrophoresis via Mass Spectrometry

Free-flow electrophoresis is a tool for the continuous fractionation of electrically charged analytes. In this study, we introduce a novel method to couple microchip-based free-flow electrophoresis with mass spectrometry. The successive connection of multiple microchip outlets to the electrospray ionization source of a mass spectrometer is automated using a multiposition valve. With this novel setup, it is possible to continuously fractionate and collect compounds while simultaneously monitoring the process online with mass spectrometry. The functionality of the method is demonstrated by the successful separation and identification of the biomolecules AMP, ATP, and CoA, which are fundamental for numerous biochemical processes in every organism.

Continuous-wave operation of DFB laser diodes based on GaN using 10$^{\rm th}$th-order laterally coupled surface gratings

Single longitudinal mode continuous-wave operation of distributed-feedback (DFB) laser diodes based on GaN is demonstrated using laterally coupled 10th-order surface Bragg gratings. The gratings consist of V-shaped grooves alongside a 1.5 µm wide p-contact stripe fabricated by using electron-beam lithography and plasma etching. By varying the period of the Bragg grating, the lasing wavelength could be adjusted between 404.8 and 408.5 nm. The feasibility of this device concept was confirmed by mode-hop-free operation up to an optical output power of 90 mW, a low temperature sensitivity of the lasing wavelength, and a Gaussian lateral far-field distribution.

Suppressing hydrogen peroxide generation to achieve oxygen-insensitivity of a [NiFe] hydrogenase in redox active films

Redox-active films were proposed as protective matrices for preventing oxidative deactivation of oxygen-sensitive catalysts such as hydrogenases for their use in fuel cells. However, the theoretical models predict quasi-infinite protection from oxygen and the aerobic half-life for hydrogenase-catalyzed hydrogen oxidation within redox films lasts only about a day. Here, we employ operando confocal microscopy to elucidate the deactivation processes. The hydrogen peroxide generated from incomplete reduction of oxygen induces the decomposition of the redox matrix rather than deactivation of the biocatalyst. We show that efficient dismutation of hydrogen peroxide by iodide extends the aerobic half-life of the catalytic film containing an oxygen-sensitive [NiFe] hydrogenase to over one week, approaching the experimental anaerobic half-life. Altogether, our data support the theory that redox films make the hydrogenases immune against the direct deactivation by oxygen and highlight the importance of suppressing hydrogen peroxide production in order to reach complete protection from oxidative stress.

Virtual staining of colon cancer tissue by label-free Raman micro-spectroscopy

The great capability of the label-free classification of tissue via vibrational spectroscopy, like Raman or infrared imaging, is shown in numerous publications (review: Diem et al., J. Biophotonics, 2013, 6, 855-886). Herein, we present a new approach, virtual staining, that improves the Raman spectral histopathology (SHP) images of colorectal cancer tissue by combining the integrated Raman intensity image in the C-H stretching region (2800-3050 cm^-1) with the pseudo-colour Raman image. This allows the display of fine structures such as the filamentous composition of muscle tissue. The morphology of the virtually stained images is in agreement with the gold standard in medical diagnosis, the haematoxylin-eosin staining. The virtual staining image also represents the whole biochemical fingerprint, and several tissue components including carcinoma were identified automatically with high sensitivity and specificity. For fast tissue classifications, a similar approach was applied on coherent anti-Stokes Raman scattering (CARS) spectral data that is faster and therefore potentially more suitable for clinical applications.

Chemical fingerprinting of single glandular trichomes of Cannabis sativa by Coherent anti-Stokes Raman scattering (CARS) microscopy

BACKGROUND

Cannabis possesses a rich spectrum of phytochemicals i.e. cannabinoids, terpenes and phenolic compounds of industrial and medicinal interests. Most of these high-value plant products are synthesised in the disk cells and stored in the secretory cavity in glandular trichomes. Conventional trichome analysis was so far based on optical microscopy, electron microscopy or extraction based methods that are either limited to spatial or chemical information. Here we combine both information to obtain the spatial distribution of distinct secondary metabolites on a single-trichome level by applying Coherent anti-Stokes Raman scattering (CARS), a microspectroscopic technique, to trichomes derived from sepals of a drug- and a fibre-type.

RESULTS

Hyperspectral CARS imaging in combination with a nonlinear unmixing method allows to identify and localise Δ⁹-tetrahydrocannabinolic acid (THCA) in the secretory cavity of drug-type trichomes and cannabidiolic acid (CBDA)/myrcene in the secretory cavity of fibre-type trichomes, thus enabling an easy discrimination between high-THCA and high-CBDA producers. A unique spectral fingerprint is found in the disk cells of drug-type trichomes, which is most similar to cannabigerolic acid (CBGA) and is not found in fibre-type trichomes. Furthermore, we differentiate between different cell types by a combination of CARS with simultaneously acquired two-photon fluorescence (TPF) of chlorophyll a from chloroplasts and organic fluorescence mainly arising from cell walls enabling 3D visualisation of the essential oil distribution and cellular structures.

CONCLUSION

Here we demonstrate a label-free and non-destructive method to analyse the distribution of secondary metabolites and distinguish between different cell and chemo-types with high spatial resolution on a single trichome. The record of chemical fingerprints of single trichomes offers the possibility to optimise growth conditions as well as guarantee a direct process control for industrially cultivated medicinal Cannabis plants. Moreover, this method is not limited to Cannabis related issues but can be widely implemented for optimising and monitoring all kinds of natural or biotechnological production processes with simultaneous spatial and chemical information.

Preventing the coffee-ring effect and aggregate sedimentation by in situ gelation of monodisperse materials

Drop-casting and inkjet printing are virtually the most versatile and cost-effective methods for depositing active materials on surfaces. However, drawbacks associated with the coffee-ring effect, as well as uncontrolled aggregation of the coating materials, have impeded the use of these methods for applications requiring high control of film properties. We now report on a simple method based on covalent cross-linking of monodisperse materials that enables the formation of thin films with homogeneous thicknesses and macroscale cohesion. The coffee-ring effect is impeded by triggering gelation of the coating materials via a thioacetate-disulfide transition which counterbalances the capillary forces induced by evaporation. Aggregates are prevented by monodisperse building blocks that ensure that the resulting gel resists sedimentation until complete droplet drying. This combined strategy yields an unprecedented level of homogeneity in the resulting film thickness in the 100 nm to 10 μm range. Moreover, macroscale cohesion is preserved as evidenced by the long-range charge transfer within the matrix. We highlight the impact of this method with bioelectrocatalysts for H2 and NADPH oxidation. Peak catalytic performances are reached at about 10-fold lower catalyst loading compared to conventional approaches owing to the high control on film cohesion and thickness homogeneity, thus setting new benchmarks in catalyst utilization.

Biochemical and pathological changes result from mutated Caveolin-3 in muscle

Background

Caveolin-3 (CAV3) is a muscle-specific protein localized to the sarcolemma. It was suggested that CAV3 is involved in the connection between the extracellular matrix (ECM) and the cytoskeleton. Caveolinopathies often go along with increased CK levels indicative of sarcolemmal damage. So far, more than 40 dominant pathogenic mutations have been described leading to several phenotypes many of which are associated with a mis-localization of the mutant protein to the Golgi. Golgi retention and endoplasmic reticulum (ER) stress has been demonstrated for the CAV3 p.P104L mutation, but further downstream pathophysiological consequences remained elusive so far.

Methods

We utilized a transgenic (p.P104L mutant) mouse model and performed proteomic profiling along with immunoprecipitation, immunofluorescence and immunoblot examinations (including examination of α-dystroglycan glycosylation), and morphological studies (electron and coherent anti-Stokes Raman scattering (CARS) microscopy) in a systematic investigation of molecular and subcellular events in p.P104L caveolinopathy.

Results

Our electron and CARS microscopic as well as immunological studies revealed Golgi and ER proliferations along with a build-up of protein aggregates further characterized by immunoprecipitation and subsequent mass spectrometry. Molecular characterization these aggregates showed affection of mitochondrial and cytoskeletal proteins which accords with our ultra-structural findings. Additional global proteomic profiling revealed vulnerability of 120 proteins in diseased quadriceps muscle supporting our previous findings and providing more general insights into the underlying pathophysiology. Moreover, our data suggested that further DGC components are altered by the perturbed protein processing machinery but are not prone to form aggregates whereas other sarcolemmal proteins are ubiquitinated or bind to p62. Although the architecture of the ER and Golgi as organelles of protein glycosylation are altered, the glycosylation of α-dystroglycan presented unchanged.

Conclusions

Our combined data classify the p.P104 caveolinopathy as an ER-Golgi disorder impairing proper protein processing and leading to aggregate formation pertaining proteins important for mitochondrial function, cytoskeleton, ECM remodeling and sarcolemmal integrity. Glycosylation of sarcolemmal proteins seems to be normal. The new pathophysiological insights might be of relevance for the development of therapeutic strategies for caveolinopathy patients targeting improved protein folding capacity.

Electronic supplementary material

The online version of this article (10.1186/s13395-018-0173-y) contains supplementary material, which is available to authorized users.

Raman fiber-optical method for colon cancer detection: Cross-validation and outlier identification approach

Endoscopy plays a major role in early recognition of cancer which is not externally accessible and therewith in increasing the survival rate. Raman spectroscopic fiber-optical approaches can help to decrease the impact on the patient, increase objectivity in tissue characterization, reduce expenses and provide a significant time advantage in endoscopy. In gastroenterology an early recognition of malign and precursor lesions is relevant. Instantaneous and precise differentiation between adenomas as precursor lesions for cancer and hyperplastic polyps on the one hand and between high and low-risk alterations on the other hand is important. Raman fiber-optical measurements of colon biopsy samples taken during colonoscopy were carried out during a clinical study, and samples of adenocarcinoma (22), tubular adenomas (141), hyperplastic polyps (79) and normal tissue (101) from 151 patients were analyzed. This allows us to focus on the bioinformatic analysis and to set stage for Raman endoscopic measurements. Since spectral differences between normal and cancerous biopsy samples are small, special care has to be taken in data analysis. Using a leave-one-patient-out cross-validation scheme, three different outlier identification methods were investigated to decrease the influence of systematic errors, like a residual risk in misplacement of the sample and spectral dilution of marker bands (esp. cancerous tissue) and therewith optimize the experimental design. Furthermore other validations methods like leave-one-sample-out and leave-one-spectrum-out cross-validation schemes were compared with leave-one-patient-out cross-validation. High-risk lesions were differentiated from low-risk lesions with a sensitivity of 79%, specificity of 74% and an accuracy of 77%, cancer and normal tissue with a sensitivity of 79%, specificity of 83% and an accuracy of 81%. Additionally applied outlier identification enabled us to improve the recognition of neoplastic biopsy samples.

A delocalized proton-binding site within a membrane protein

The role of protein-bound water molecules in protein function and catalysis is an emerging topic. Here, we studied the solvation of an excess proton by protein-bound water molecules and the contribution of the surrounding amino acid residues at the proton release site of the membrane protein bacteriorhodopsin. It hosts an excess proton within a protein-bound water cluster, which is hydrogen bonded to several surrounding amino acids. Indicative of delocalization is a broad continuum absorbance experimentally observed by time-resolved Fourier transform infrared spectroscopy. In combination with site-directed mutagenesis, the involvement of several amino acids (especially Glu-194 and Glu-204) in the delocalization was elaborated. Details regarding the contributions of the glutamates and water molecules to the delocalization mode in biomolecular simulations are controversial. We carried out quantum mechanics/molecular mechanics (QM/MM) self-consistent charge density functional tight-binding simulations for all amino acids that have been experimentally shown to be involved in solvation of the excess proton, and systematically investigated the influence of the quantum box size. We compared calculated theoretical infrared spectra with experimental ones as a measure for the correct description of excess proton delocalization. A continuum absorbance can only be observed for small quantum boxes containing few amino acids and/or water molecules. Larger quantum boxes, including all experimentally shown involved amino acids, resulted in narrow absorbance bands, indicating protonation of a single binding site in contradiction to experimental results. We conclude that small quantum boxes seem to reproduce representative extreme cases of proton delocalization modes: proton delocalization only on water molecules or only between Glu-194 and Glu-204. Extending the experimental spectral region to lower wave numbers, a water-delocalized proton reproduces the observed continuum absorbance better than a glutamate-shared delocalized proton. However, a full agreement between QM simulations and experimental results on the delocalized excess proton will require a larger quantum box as well as more sophisticated QM/MM methods.

Infrared spectral marker bands characterizing a transient water wire inside a hydrophobic membrane protein

Proton conduction along protein-bound "water wires" is an essential feature in membrane proteins. Here, we analyze in detail a transient water wire, which conducts protons via a hydrophobic barrier within a membrane protein to create a proton gradient. It is formed only for a millisecond out of three water molecules distributed at inactive positions in a polar environment in the ground state. The movement into a hydrophobic environment causes characteristic shifts of the water bands reflecting their different chemical properties. These band shifts are identified by time-resolved Fourier Transform Infrared difference spectroscopy and analyzed by biomolecular Quantum Mechanical/Molecular Mechanical simulations. A non-hydrogen bonded ("dangling") O-H stretching vibration band and a broad continuum absorbance caused by a combined vibration along the water wire are identified as characteristic marker bands of such water wires in a hydrophobic environment. The results provide a basic understanding of water wires in hydrophobic environments.

Colocalization of fluorescence and Raman microscopic images for the identification of subcellular compartments: a validation study

This paper introduces algorithms for identifying overlapping observations between Raman and fluorescence microscopic images of one and the same sample.

Automated identification of subcellular organelles by coherent anti-stokes Raman scattering

Coherent anti-Stokes Raman scattering (CARS) is an emerging tool for label-free characterization of living cells. Here, unsupervised multivariate analysis of CARS datasets was used to visualize the subcellular compartments. In addition, a supervised learning algorithm based on the "random forest" ensemble learning method as a classifier, was trained with CARS spectra using immunofluorescence images as a reference. The supervised classifier was then used, to our knowledge for the first time, to automatically identify lipid droplets, nucleus, nucleoli, and endoplasmic reticulum in datasets that are not used for training. These four subcellular components were simultaneously and label-free monitored instead of using several fluorescent labels. These results open new avenues for label-free time-resolved investigation of subcellular components in different cells, especially cancer cells.

The role of protein-bound water molecules in microbial rhodopsins

Protein-bound internal water molecules are essential features of the structure and function of microbial rhodopsins. Besides structural stabilization, they act as proton conductors and even proton storage sites. Currently, the most understood model system exhibiting such features is bacteriorhodopsin (bR). During the last 20 years, the importance of water molecules for proton transport has been revealed through this protein. It has been shown that water molecules are as essential as amino acids for proton transport and biological function. In this review, we present an overview of the historical development of this research on bR. We furthermore summarize the recently discovered protein-bound water features associated with proton transport. Specifically, we discuss a pentameric water/amino acid arrangement close to the protonated Schiff base as central proton-binding site, a protonated water cluster as proton storage site at the proton-release site, and a transient linear water chain at the proton uptake site. We highlight how protein conformational changes reposition or reorient internal water molecules, thereby guiding proton transport. Last, we compare the water positions in bR with those in other microbial rhodopsins to elucidate how protein-bound water molecules guide the function of microbial rhodopsins. This article is part of a Special Issue entitled: Retinal Proteins - You can teach an old dog new tricks.

Nanoscale distinction of membrane patches--a TERS study of Halobacterium salinarum

The structural organization of cellular membranes has an essential influence on their functionality. The membrane surfaces currently are considered to consist of various distinct patches, which play an important role in many processes, however, not all parameters such as size and distribution are fully determined. In this study, purple membrane (PM) patches isolated from Halobacterium salinarum were investigated in a first step using TERS (tip-enhanced Raman spectroscopy). The characteristic Raman modes of the resonantly enhanced component of the purple membrane lattice, the retinal moiety of bacteriorhodopsin, were found to be suitable as PM markers. In a subsequent experiment a single Halobacterium salinarum was investigated with TERS. By means of the PM marker bands it was feasible to identify and localize PM patches on the bacterial surface. The size of these areas was determined to be a few hundred nanometers.

In channelrhodopsin-2 Glu-90 is crucial for ion selectivity and is deprotonated during the photocycle

The light-activated microbial ion channel channelrhodopsin-2 (ChR2) is a powerful tool to study cellular processes with high spatiotemporal resolution in the emerging field of optogenetics. To customize the channel properties for optogenetic experiments, a detailed understanding of its molecular reaction mechanism is essential. Here, Glu-90, a key residue involved in the gating and selectivity mechanism of the ion channel is characterized in detail. The deprotonation of Glu-90 during the photocycle is elucidated by time-resolved FTIR spectroscopy, which seems to be part of the opening mechanism of the conductive pore. Furthermore, Glu-90 is crucial to ion selectivity as also revealed by mutation of this residue combined with voltage clamp experiments. By dynamic homology modeling, we further hypothesized that the conductive pore is flanked by Glu-90 and located between helices A, B, C, and G.

How does a membrane protein achieve a vectorial proton transfer via water molecules?

We present a detailed mechanism for the proton transfer from a protein-bound protonated water cluster to the bulk water directed by protein side chains in the membrane protein bacteriorhodopsin. We use a combined approach of time-resolved Fourier transform infrared spectroscopy, molecular dynamics simulations, and X-ray structure analysis to elucidate the functional role of a hydrogen bond between Ser193 and Glu204. These two residues seal the internal protonated water cluster from the bulk water and the protein surface. During the photocycle of bacteriorhodopsin, a transient protonation of Glu204 leads to a breaking of this hydrogen bond. This breaking opens the gate to the extracellular bulk water, leading to a subsequent proton release from the protonated water cluster. We show in detail how the protein achieves vectorial proton transfer via protonated water clusters in contrast to random proton transfer in liquid water.

Long-term glucose control in patients with pancreatic transplants

OBJECTIVE

To evaluate the long-term effect on blood glucose levels of successful transplantation of part or all of an intact human pancreas in patients with insulin-dependent diabetes mellitus (IDDM).

DESIGN

Cohort study.

SETTING

Referral medical center.

PATIENTS

Thirty-seven patients with adequate data, representative of a group of 62 patients with functioning grafts (that is, insulin-independent) at 2 years after transplantation. The 62 patients came from a total of 178 patients in the University of Minnesota series as of July 1987, for a 2-year success rate of 35% (95% Cl, 27.8% to 41.8%). These patients were compared to two diabetic control groups (18 patients with IDDM under standard insulin treatment in a university diabetes clinic and 11 patients with IDDM whose pancreas grafts had failed) and to two nondiabetic groups (14 nondiabetic patients who received immunosuppressive drugs after kidney transplantation and 196 healthy control subjects).

MEASUREMENTS

Glycosylated hemoglobin was measured by the high-pressure liquid chromatography method, as total A1 (Hb A1) and the A1C subfraction (Hb A1C); results were expressed as a percentage of total hemoglobin.

MAIN RESULTS

Before pancreas transplantation, the 37 patients in the study group had a mean Hb A1 of 10.8%, consistent with moderate to marked hyperglycemia and not statistically different from the levels in the diabetic control groups. All 37 patients had values above the therapeutic target range of 5.4% to 7.4%. However, at 1 and 2 years after transplantation, the mean Hb A1 value had fallen sharply to 6.7% and 6.5%, respectively, well within target range (Cl of the difference, 3.4% to 4.8%; P less than 0.001). These levels did not differ from the mean Hb A1 in the nondiabetic kidney transplant recipients but were slightly above the 6.2% value for the 196 healthy controls (Cl of the difference at 1 year, 0.2% to 0.8%). Serial values were available on 6 subjects for 5 years; these values were all well within target range. As expected, Hb A1C values were parallel to those of Hb A1.

CONCLUSIONS

Pancreas transplantation, in our successful cases, lowered glycosylated hemoglobin to normal or near-normal levels that were sustained for as long as 5 years. These results compare favorably with those in our patients on standard treatment, and also with those in similar patients on intensive control reported by others. Further effort to improve transplant methods appears to be warranted.

Contribution of monocyte-macrophage system to serum alpha 1-antitrypsin

The major serum antiprotease is alpha 1-antitrypsin (A1AT). Deficiency of A1AT can result in infantile cirrhosis and premature emphysema, both of which have a high degree of morbidity and significant mortality. Although synthesized primarily by the liver, A1AT has been histochemically localized in monocytes and macrophages in vitro and has been shown to be produced in tissue culture of monocyte-macrophage origin. This study was planned to quantitatively and qualitatively assess the in vivo monocyte-macrophage system contribution to serum A1AT. We used bone marrow transplantation (BMT) as an experimental method because there is commanding evidence that after engraftment, the monocyte-macrophage system of the recipient is replaced by that of donor origin. Protease inhibitor (Pi) typing was done on 150 potential BMT recipients and on their potential donors before transplantation. From these initial recipients, 92 eventually underwent transplantation, and 11 recipient-donor pairs, in which each donor's Pi type contained a band not in the recipient's Pi type, were chosen for the study. Six recipients survived beyond 100 days after BMT, and in these cases the donor contained either an S or an M2 band in his or her Pi type not present in the recipient. Using a silver stain method on diluted serum of known M1M2 and MS types, we were able to detect a 2% dilution of the S band and a 25% dilution of the M2 band. When the same method was applied to gels used in typing recipient Pi after BMT, we were unable to detect any contribution to serum A1AT by the donor monocyte-macrophage system.

Fatal liver disease associated with alpha 1-antitrypsin deficiency PiM1/PiMduarte

A 53-yr-old man with a rare form of partial alpha 1-antitrypsin deficiency, PiM1/PiMduarte, died of endstage cirrhosis. Typical cytoplasmic alpha 1-antitrypsin globules were present in the hepatocyte cytoplasm. Initial protease inhibitor phenotyping on the patient was reported as normal PiM1 in more than one laboratory. This case emphasizes the diagnostic importance of alpha 1-antitrypsin and illustrates the point that protease inhibitor phenotyping without family genotyping may be misleading in heterozygous patients with liver disease.

Lactose absorption and mucosal disaccharidases in convalescent pellagra and kwashiorkor children

Oral lactose and glucose/galactose loading tests were done in Bantu children convalescing from kwashiorkor and pellagra. Small bowel biopsies and disaccharidase estimations were performed in all except 2 patients. Lactose absorption was more impaired and intestinal lactase levels were lower in the pellagra than in the kwashiorkor group. The fact that diarrhoea after admission to hospital was less common in pellagra than kwashiorkor was ascribed to a lesser lactose load due to the early introduction of a mixed diet in the former group, in comparison with milk feeds only in the latter group. The absence of troublesome diarrhoea while on moderate quantities of lactose in the diet, in the presence of low intestinal lactase levels, but evidence of lactose malabsorption after loading, has a bearing on preventive and therapeutic nutrition programmes in non-Caucasian children. Lactase deficiency is not necessarily synonymous with symptomatic lactose intolerance if the threshold is not exceeded. Concern is expressed that excessive caution against the use of milk may lead to a worsening of infantile malnutrition in developing countries.