A five-level classification system for proteoform identifications

To the editor The term proteoform, introduced in Nature Methods in 2013 (ref. 1), has rapidly gained acceptance in the proteomics community. The challenge and importance of comprehensively identifying proteoforms in complex samples has been recognized, and reports have begun to appear of new platforms towards that end2,3,4,5. However, one interesting central ambiguity has emerged, namely determining precisely what is meant by a ‘proteoform...