Automated chip-based nanoelectrospray-mass spectrometry for rapid identification of proteins separated by two-dimensional gel electrophoresis

We report a method using a fully automated chip-based nanoelectrospray system for two-dimensional (2-D) gel sample analyses with mass spectrometric detection. The automated nanoelectrospray system, consisting of the NanoMate and electrospray ionization (ESI) chip, serves as both an autosampler and nanoESI source. This infusion system aspirates samples from a 96-well plate using disposable pipette tips and then delivers these samples sequentially to an ESI chip. This chip is a fully integrated monolithic device consisting of a 10 x 10 array of nozzles. The automated nanoelectrospray system is easily controlled through software, permitting the user to select the number of samples to be analyzed, the volume of sample to aspirate, the spray voltage, and analysis time. The system offers all the advantages of conventional nanoelectrospray plus automated, high-throughput analyses without analyte carryover. The system was used for a protein identification study of 2-D gel spots of both Escherichia coli and yeast crude cell extracts. The identification of 50 spots from E coli crude cell extract and 27 spots from yeast extract is presented, demonstrating the powerful combination of the automated nanoESI system, the Thermo Finnigan LCQ Deca ion-trap mass spectrometer, and SEQUEST search software. In addition, the effects of silver staining and colloidal Coomassie blue staining of 2-D gel spots on the detection sensitivity and protein sequence coverage are compared and discussed. Furthermore, the comparison results using the multiwell microscale preparation kit versus manual extraction for in-gel samples are presented.