Identification and affinity-quantification of ß-amyloid and α-synuclein polypeptides using on-line SAW-biosensor-mass spectrometry

Epitope characterization of proteins and aptamers with mass spectrometry

The way in which professor Michael Przybylski has combined the spirit of research with entrepreneurship has set an example for any and all scientists. He has made significant achievements in the fields of mass spectrometry, biochemistry and medicine, and has initiated important technological developments in the area of protein analysis. Between 2016 and 2023 professor Przybylski's scientific focus shifted on protein interactions with emphasis on aptamer-protein and antibody-protein analysis. This review focuses on professor Przybylski's achievements in the last few years highlighting his impact on the scientific community, on his students and colleagues.

Michael Przybylski (1948-2023) Devoted Half a Century to Mass Spectrometry

Michael Przybylski (1948-2023) was a Polymer Chemist by training and devoted nearly his entire scientific life, almost 50 years, to mass spectrometry and its biomedical applications. After earning his PhD in Chemistry, there followed a Postdoc stay at the National Cancer Institute, Bethesda, MD, USA, and his habilitation at the University of Mainz, Germany. Soon thereafter, Michael Przybylski took the Chair for Analytical Chemistry at the University of Konstanz, Germany, where he served as Director of the Analytical Chemistry and Biopolymer Structure Analysis Laboratory. As Emeritus Michael Przybylski moved the Steinbeis Centre for Biopolymer Analytics and Biomedical Mass Spectrometry to Rüsselsheim, Germany. Michael Przybylski's research was from the beginning interdisciplinary-oriented and in many ways groundbreaking: leading to over 400 scientific papers published in internationally renowned journals and to about 25 patents. Michael Przybylski gave approximately 150 invited lectures and was awarded several scientific prizes. In recognition of his outstanding achievements and fruitful collaboration, he received the Doctorate of honor from the "Alexandru Ioan Cuza" University of Iaşi, Romania. Michael Przybylski was the Director of the by him founded "Biopolymer Analytics and Biomedical Mass Spectrometry" research center until his sudden and unexpected death.

An Electrochemical Immunosensor Based on a Self-Assembled Monolayer Modified Electrode for Label-Free Detection of α-Synuclein

This research demonstrated the development of a simple, cost-effective, and label-free immunosensor for the detection of α-synuclein (α-Syn) based on a cystamine (CYS) self-assembled monolayer (SAM) decorated fluorine-doped tin oxide (FTO) electrode. CYS-SAM was formed onto the FTO electrode by the adsorption of CYS molecules through the head sulfur groups. The free amine (–NH₂) groups at the tail of the CYS-SAM enabled the immobilization of anti-α-Syn-antibody, which concurrently allowed the formation of immunocomplex by covalent bonding with α-Syn-antigen. The variation of the concentrations of the attached α-Syn at the immunosensor probe induced the alternation of the current and the charge transfer resistance (R_ct) for the redox response of [Fe(CN)₆]^3−/4−, which displayed a linear dynamic range from 10 to 1000 ng/mL with a low detection limit (S/N = 3) of ca. 3.62 and 1.13 ng/mL in differential pulse voltammetry (DPV) and electrochemical impedance spectra (EIS) measurements, respectively. The immunosensor displayed good reproducibility, anti-interference ability, and good recoveries of α-Syn detection in diluted human serum samples. The proposed immunosensor is a promising platform to detect α-Syn for the early diagnose of Parkinson’s disease, which can be extended for the determination of other biologically important biomarkers.

Large-Scale Identification and Fragmentation Pathways Analysis of N-Glycans from Mouse Brain

N-linked glycosylation is one of the most common protein PTMs, and the topological structure (monosaccharide composition and sequence as well as glycosidic linkages) of N-glycans is vital information to understand their biological functions and roles. Tandem mass spectrometry has been widely used for topological structure characterization of N-glycans, where comprehensive understanding of fragmentation pathways and characteristics of product ions are essential to achieve best interpretation of MS/MS data and highest confidence of identification. Here, we report our glycomic study of N-glycome of mouse brain as well as fragmentation pathway analysis of the identified N-glycans. With LC-MS/MS analysis at both the positive and negative ESI modes together with our recently developed N-glycan database search engine GlySeeker, 221 unique N-glycans with putative topological structures were identified with target-decoy searches and number of best hits of 1. Analysis of fragmentation pathways and characteristics of product ions of permethylated N-glycans in the positive mode and native N-glycans in the negative mode were further carried out. The reported N-glycans serve as a basic reference for future glycosylation study of mouse brain; and in general database search of tandem mass spectra of N-glycans, B/Y/Z ions should be preferentially considered for the permethylated form in the positive mode and B/C/Z ions for the native form in the negative mode.

Specific expression pattern of tissue cytokines analyzed through the Surface Acoustic Wave technique is associated with age-related spontaneous benign prostatic hyperplasia in rats

The aim of the study reported herein was to evaluate the suitability of the Surface Acoustic Wave (SAW) technique as a possible diagnostic tool in benign prostatic hyperplasia (BPH). Moreover, for the first time, the BPH model was a totally physiological using naturally aged rats with spontaneous, age-related BPH instead of the pharmacologically induced models usually used. Eighteen male Wistar rats were distributed according to their age: 6 weeks (young), 12 weeks (adult) and 12 months (old) old. Prostate gland was removed and analyzed by mini-arrays, Western blotting (WB) and SAW techniques. Mini-arrays indicated that there were significant differences in the expression of 29/34 inflammation-related cytokines. WB was carried out to confirm the results after selection of 4 cytokines from which one showed no changes, namely PDGF-AA, and the other three, which significantly increase in older animals, were CD86, β-NGF and VEGF. Notwithstanding, WB of old rats yielded confusing results due to an anomalous migration of proteins, dismissing this technique as an useful tool in these animals. Accurate results in old rats were uniquely obtained by using the SAW technique. Thus, SAW analysis showed that there were not differences among groups in the amount of PDGF-AA. On the contrary, SAW analysis showed that amounts of CD86, β-NGF and VEGF in old rats were 2.0, 1.9 and 5.7-fold higher than that from young ones, respectively. These results indicate that SAW is a highly accurate technique for determining changes in the cytokines expression in BPH.

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Diagnosis of prostate alterations can be improved by using the SAW technique.

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Study of prostate alterations can be optimized by using an age-related animal model.

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VEGF is a sensitive marker of bening prostatic hyperplasia.

Validation of electrochemiluminescence assays for highly sensitive and reproducible quantification of α-synuclein in cerebrospinal fluid

AIM

α-Synuclein (aSyn), a putative cerebrospinal fluid biomarker, may support the diagnosis of neurodegenerative diseases. Previous studies led to conflicting results due to different preanalytical and analytical procedures. Standardized assays are required to allow for comparison of results from different laboratories.

MATERIALS & METHODS

We performed a side-by-side validation of a commercially available (MSD, MD, USA) and a 'homebrew' assay for quantification of aSyn according to published guidelines.

RESULTS

The data showed high sensitivity and reproducibility for both assays. Preanalytical and analytical parameters did not affect the outcome of measurements.

CONCLUSION

We conclude that both assays are very close in performance and suitable for research application of cerebrospinal fluid aSyn.

Mass-Sensitive Biosensor Systems to Determine the Membrane Interaction of Analytes

Biosensors are devices that transform a biological interaction into a readout signal, which is evaluable for analytical purposes. The general strength of biosensor approaches is the avoidance of time-consuming and cost-intensive labeling procedures of the analytes. In this chapter, we give insight into a mass-sensitive surface-acoustic wave (SAW) biosensor, which represents an elegant and highly sensitive method to investigate binding events at a molecular level. The principle of SAW technology is based on the piezoelectric properties of the sensors, so as to binding events and their accompanied mass increase at the sensor surface are detectable by a change in the oscillation of the surface acoustic wave. In combination with model membranes, transferred to the sensor surface, the analytical value of SAW biosensors has strongly been increased and extended to different topics of biomedical investigations, including antibiotic research. The interaction with the bacterial membrane or certain target structures therein is the essential mode of action for various antibacterial compounds. Beside targeted interaction, an unspecific membrane binding or membrane insertion of drugs can contribute to the antibacterial activity by changing the lateral order of membrane constituents or by interfering with the membrane barrier function. Those pleiotropic effects are hardly to illustrate in the bacterial systems and need a detailed view at the in vitro level. Here, we illustrate the usefulness of a SAW biosensor in combination with model membranes to investigate the mode of membrane interaction of antibiotic active peptides. Using two different peptides we exemplary describe the interaction analysis in a two-step gain of information: (1) a binding intensity or affinity by analyzing the phase changes of oscillation, and (2) mode of membrane interaction, i.e., surface binding or internalization of the peptide by following the amplitude of oscillation.

Chemical Functionalization of Germanium with Dextran Brushes for Immobilization of Proteins Revealed by Attenuated Total Reflection Fourier Transform Infrared Difference Spectroscopy

Protein immobilization studied by attenuated total reflection Fourier transform infrared (ATR-FT-IR) difference spectroscopy is an emerging field enabling the study of proteins at atomic detail. Gold or glass surfaces are frequently used for protein immobilization. Here, we present an alternative method for protein immobilization on germanium. Because of its high refractive index and broad spectral window germanium is the best material for ATR-FT-IR spectroscopy of thin layers. So far, this technique was mainly used for protein monolayers, which lead to a limited signal-to-noise ratio. Further, undesired protein-protein interactions can occur in a dense layer. Here, the germanium surface was functionalized with thiols and stepwise a dextran brush was generated. Each step was monitored by ATR-FT-IR spectroscopy. We compared a 70 kDa dextran with a 500 kDa dextran regarding the binding properties. All surfaces were characterized by atomic force microscopy, revealing thicknesses between 40 and 110 nm. To analyze the capability of our system we utilized N-Ras on mono-NTA (nitrilotriacetic acid) functionalized dextran, and the amount of immobilized Ras corresponded to several monolayers. The protein stability and loading capacity was further improved by means of tris-NTA for immobilization. Small-molecule-induced changes were revealed with an over 3 times higher signal-to-noise ratio compared to monolayers. This improvement may allow the observation of very small and so far hidden changes in proteins upon stimulus. Furthermore, we immobilized green fluorescent protein (GFP) and mCherry simultaneously enabling an analysis of the surface by fluorescence microscopy. The absence of a Förster resonance energy transfer (FRET) signal demonstrated a large protein-protein distance, indicating an even distribution of the protein within the dextran.