Proteome analysis of human hair shaft: from protein identification to posttranslational modification

The human hair proteome was investigated using two-dimensional LC-MS/MS. Among the 343 identified proteins, 70 were detected in high relative abundance, including keratin intermediate filament proteins, largely extractable with denaturants. Over 300 proteins were found to constitute the insoluble complex formed by transglutaminase cross-linking. The intracellular distribution of identified proteins is wide from cytoplasm to nucleus, mitochondria, ribosome, and plasma membrane. These results help rationalize ultrastructural features visible in the mature hair. Keratins and several substrates for transglutaminase were found to be posttranslationally modified by methylation and dimethylation. Evidence for ubiquitination of hair proteins was also obtained.