Solid-phase derivatization of tryptic peptides for rapid protein identification by matrix-assisted laser desorption/ionization mass spectrometry.

Solid-phase sulfonation of tryptic peptides adsorbed to C18 muZipTips has been carried out to facilitate de novo sequencing with mass spectrometry. Peptides are reacted with the sulfonation reagent while they are still adsorbed to the solid phase. Excess reagent passes through the ZipTip to waste. Washing the products before subsequent elution from the mini-column also affords sample cleanup prior to analysis. Near quantitative N-terminal sulfonation can be achieved reliably at room temperature in only a few seconds. The method has been applied successfully to model peptides and to solution or in-gel digests of proteins. Current sequencing limits are about 100 fmol of protein. Multiplexed sample sulfonation reactions have been carried out with a manual 8-position micropipettor or using centrifugal force to reliably pass reagents and wash solutions over sample-loaded ZipTips. With multiplexing, overall preparation times have been reduced to about 1 min per sample. The solid-phase format facilitates efficient use of precious digest samples by enabling them to be recovered from the matrix-assisted laser desorption/ionization (MALDI) sample stage after mass fingerprinting, derivatized and re-analyzed by MALDI postsource decay mass spectrometry.