| Description | This approach leads to protein identification by combining mass measurement and short amino acid sequence information obtained by tandem mass spectrometry. This information is then used to automatically find the best match in a sequence database. A mixture of peptides derived from a protease digestion is analysed by nanoelectrospray LC-MS/MS (Liquid Chromatography Tandem Mass Spectrometer or nanoESI MS/MS) mass spectrometry. Electrospray mass spectrometry cannot be applied to dilute samples and is affected by high salt. As a consequence peptides, normally extracted from acrylamide gels by in situ proteolysis, are desalted and concentrated on a microcolumn followed by elution into a capillary used for nanoelectrospray tandem mass spectrometry. A first mass spectrum (Normal mass spectrum or Q1 mass spectrum) gives information about the masses of all the peptides. Peptides observed in the normal mass spectrum are isolated in turn and dissociated into fragments by collision with gas molecules within the mass spectrometer. Some of the fragments obtained from a peptide constitute a nested set, differing by one amino acid, and the mass difference between them allows assignment of a partial sequence. The masses of the fragments define the position of the partial sequence in the peptide. Together with the cleavage specificity of the protease used to cleave the protein, and mass information such sequence tag provides much higher search specificity to match the a database entry. The procedure is repeated with several peptides from the digest, resulting in multiple identifications of the same protein or identification of several proteins from the peptide mixture. Unknown proteins can easily be identified by using the high specificity of the peptide sequence tag for searches in most sequence databases including EST or genome databases. | Namespace | PSI-MI |
| Obsolete | false |
Ontology Term --> All ancestors
Ontology Term --> All descendants
Ontology Term --> Direct children
Ontology Term --> Direct parents
