Identification of unusual amino acids in peptides using automated sequential Edman degradation coupled to direct detection by electrospray-ionizationmass spectrometry

The determination of the primary structure of peptides and proteins is rout ine in many laboratories; however; many of the obtained sequences are incom plete or can be misinterpreted, then the samples contain unusual amino acid s. Here we report the development of an automated peptide sequenator couple d to nit electrospray-ionization (ESI) mass spectrometer (MS) that, in conj unction with minor modifications to the sequencing conditions and in some c ases, prior derivatization of amino acids, allows the detection of the phen ylthiohydantoin (PTH) derivatives of a number of unusual amino acids. Using the coupled sequenator-ESI-MS system we It ere able to determine the compl ete sequence of the lantibiotic gallidermin, a partial sequence of the calc ium-dependent peptide antibiotic CDA2 as well as the pool sequence of a mix ture of synthetic synthetic peptides containing nonproteinogenic amino acid s. In addition to the 20 proteinogenic amino acids, the procedure was able to detect PTH derivatives of hydroxyphenylglycine, 2,3-didehydroasparagine, 3-methylglutamic acid, oxytryptophan, ornithine, N-methylglycine, dihydrox yphenylalanine, and alpha-aminoisobutyric acid. Similarly, after a simple d erivatization procedure, we were also able to correctly identify educts of 2,3-didehydronlanine, 2,3-didehydrobutyrine, lanthionine, and 3-methyllanth ionine. (C) 1999 John Wiley & Sons, Inc.