Electroelution of nonfluorescent stacked proteins detected by fluorescence optics from gel electrophoretic bands for transfer into mass spectrometry

Sequential electroelution and mass spectroscopic identification of intact sodium dodecyl sulfate-proteins labeled with 5(6)-carboxyfluorescein-N-hydroxysuccinimide ester

A gel electrophoresis apparatus capable of scanning the migration path fluorometrically and of computer-directed electroelution of bands was applied to the mass spectrometric identification of sequentially electroeluted 5(6)-carboxyfluorescein-N-hydrosuccinimide ester (FLUOS)-labeled sodium dodedyl sulfate (SDS)-proteins. The masses of four electroeluted SDS-proteins under study determined by matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) spectrometry are changed by 1% due to their reaction with FLUOS in a 1:5 molar ratio of protein:label, allowing for the identification of the labeled intact proteins on the basis of mass. More importantly, the partial (10 or 50%) derivatization of proteins with FLUOS does not preclude their tryptic hydrolysis, and identification of the protein on the basis of the mass spectrometric analysis of its tryptic peptides. Potentially, the procedure allows for the automated mass spectrometric identification of SDS-proteins globally labeled with FLUOS and electrophoretically separated, without need for any gel sectioning.

Stacking of unlabeled sodium dodecyl sulfate-proteins within a fluorimetrically detected moving boundary, electroelution and mass spectrometric identification

The previously reported fluorimetric detection of sodium dodecyl sulfate (SDS)-protein in the presence of cascade blue in agarose gel electrophoresis using barbital buffer was found to be equally feasible in the absence of the fluorescent marker and using Tris-Tricinate buffer, provided that SDS was loaded with the sample but not contained in the catholyte. That fluorescent detection is thought to be due to the formation of a moving boundary between leading SDS and trailing barbital, or Tricinate buffer. This hypothesis is supported by the following evidence: (i) The fluorometrically detected band disappears with addition of SDS to the catholyte; (ii) band area is proportional to protein and/or SDS load; (iii) mobility of SDS-proteins differing in mass is the same at agarose concentrations up to 3%; (iv) lowering of protein mobility by increase in gel concentration and/or increase in the size of the SDS-protein leads to band disappearance. Fluorescent detection of the band is like to be nonspecific and due to the light scattering properties of a stack comprising moving boundaries of any analytes with net mobilities intermediate between SDS (or micellar SDS) and the trailing buffer constituent at their regulated very high concentrations. The steady-state stack of SDS-proteins in the size range of 14.4-45.0 kDa, and the transient stack of an SDS-protein of 66.2 kDa have lent themselves to electroelution and characterization by mass of the proteins after removal of SDS and buffer exchange using matrix assisted laser desorption/ionization-time of flight (MALDI-TOF)-mass spectrometry. The possibility to form a stack of protein between leading SDS and trailing buffer anions under conditions of weak molecular sieving (open-pore gel and small-sized protein) contributes to the understanding of moving boundaries in gel electrophoresis, but in view of the narrowly defined conditions, under which this stack forms, is of limited practical significance for the gel electrophoresis of SDS-proteins.

Recovery of sodium dodecyl sulfate-proteins from gel electrophoretic bands in a single electroelution step for mass spectrometric analysis

Mass spectrometric analysis of proteins derived from bands in gel electrophoresis is incompatible with the covalent fluorescent labeling of the protein. Thus, if one wishes to take advantage of the capacity for computer-directed electroelution of electrophoresis apparatus with intermittent fluorescent scanning of the migration path, the protein must be labeled fluorescently in a noncovalent, reversible fashion. This was recently achieved by staining of SDS-proteins with Cascade blue and electrophoresis in barbital buffer. However, the method was not a practical one for the purpose of isolating proteins from gel electrophoretic bands and their transfer into the mass spectrometer for three reasons: (i) Ten consecutive electroelution steps were required to obviate pH changes in the electroelution chamber; (ii) electroeluates from six gel electrophoretic lanes needed to be pooled; (iii) excessive protein loads ranging from 7 to 33 microg/pool were required. The present study reports the solution to those three problems. Mass spectrometric (MALDI-TOF) characterization of five proteins was demonstrated (i) after a single electroelution step; (ii) using electroelution from a single gel of 0.3-cm(2) cross-sectional area; and (iii) using a protein load of 2 (in one case 4) microg. However, the migration rates of the Cascade blue-SDS-protein-barbital complexes derived from proteins with widely varying molecular weights proved to be the same. Thus, despite the three advances made, the method to date remains restricted to samples of single proteins.

Current awareness

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Books, Reviews & Symposia; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (6 Weeks journals - Search completed at 7th. June 2000)