Investigation of charge variants of rViscumin by two-dimensional gel electrophoresis and mass spectrometry.

A method for the analysis of the rViscumin heterodimer (recombinant mistletoe lectin) based on two-dimensional (2-D) polyacrylamide gel electrophoresis and mass spectrometry was developed and used for quality control concerning purity and homogeneity of the recombinant protein processed under Good Manufacturing Practice (GMP) conditions. A series of spots with different pI-values in the pH-gradient of both rViscumin A- and B-chain were observed independently from the experimental conditions like urea concentration, heat treatment or the use of cysteine alkylating agents. Comparative studies of the major spots using matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS), liquid chromatography-electrospray ionization (LC-ESI)-MS and LC-ESI-tandem MS (MS/MS) after tryptic in-gel digestion resulted in a sequence coverage of 92% for the A-chain and 95% for the B-chain. No molecular differences like common chemical or post-translational modifications or nonenzymatic deamidation were found to cause the different charge values of the separated spots. Therefore, these protein spots were extracted from the 2-D gel and separated again by 2-D gel electrophoresis (termed Re-2-DE). Each of the single spots tested in the Re-2-DE experiment split up in the same heterogeneous pattern concerning the pI-values. We suggest that the observed charge variants of rViscumin are the result of conformational protein variants, existing in an equilibrium during sample preparation and/or isoelectric focusing and are not caused from microheterogeneity in the primary structure of rViscumin.

Identification of proteins from human cerebrospinal fluid, separated by two-dimensional polyacrylamide gel electrophoresis.

The aim of this work is to display the protein composition of the cerebrospinal fluid by two-dimensional (2-D) gel electrophoresis and identify it using different mass spectrometric techniques. This will enable us to present an overview of the proteins in human cerebrospinal fluid. The comparison of 2-D gels will help us to analyze the normal protein variability in healthy persons and specific protein variations in patients with different neurological diseases (e.g., morbus Alzheimer, chorea Huntington). However, it is not possible to carry out 2-D gel electrophoresis directly with human cerebrospinal fluid due to the high amount of salts, sugars and lipids present. In addition, the total amount of protein is only as high as 0.3-0.7 microg/microL. Therefore, concentration and desalting steps using precipitation and ultrafiltration are necessary. To date we have been able to identify more than 65 spots from 2-D gels using matrix assisted laser desorption/ionization-mass spectrometry and electrospray ionization-mass spectrometry.