Updated project metadata. Proteins and protein N termini were isolated and enriched from human erythrocytes following the TAILS procedure with heavy dimethyl labeling of free N-termini (Kleifeld et al. Nat Biothech 2010). Following LC-MS/MS analysis on a Thermo Orbitrap XL spectra were matched using Mascot, X!Tandem and MSGF+ databases search engines and trans proteomic pipeline (TPP) modules for statistical evaluation. Maximum peptide level FDR was set to 1% (iProphet probability 0.88) and protein level FDR to 0.7% (proteinProphet probability 0.9).