Emerging methods in proteomics: top-down protein characterization by multistage tandem mass spectrometry.

"Top-down" mass spectrometry methods have emerged as an attractive alternative to conventional "bottom-up" approaches for the comprehensive characterization of co- and post-translational protein modifications. Here we present a brief overview of current strategies employed for top-down protein characterization and discuss the key technical challenges and solutions associated with their implementation on a range of mass spectrometry instrument platforms. For more specific details regarding the individual strategies described herein, interested readers are referred to the references cited at the end of this article.