Potential Use of Human Hair Shaft Keratin Peptide Signatures to Distinguish Gender and Ethnicity

The study investigated the molecular structure of human hair using high-resolution X-ray diffraction, focusing on differences between individuals, including genetic similarities. Despite a small sample size of 12 individuals, the research found that the general molecular features of hair, such as the coiled-coil phase of α-helical keratin proteins and lipid layers, were consistent across all samples. However, variations in lipid types were noted, suggesting genetic influence, as identical patterns appeared in hair from genetically similar individuals like identical twins and a father-daughter pair, but not in fraternal twins. These findings highlighted the potential of using hair's molecular structure as a diagnostic tool for diseases.

The study examined the content and distribution of lipids in African, Asian, and Caucasian hair, focusing on how these lipids interact with keratin, the main structural protein in hair. It was found that African hair contained a higher percentage of internal lipids compared to other ethnic hair types. This higher lipid content influenced the structure of keratin, as evidenced by the absence of axial diffraction in X-ray analysis, which returned to normal after lipid removal. Molecular dynamics simulations showed that lipids intercalated with keratin dimers, altering their structure. The study concluded that the keratin structure in African hair might be influenced by its higher lipid concentration.

The study characterized the human hair keratin-associated protein 2 (KRTAP2) gene family, revealing size polymorphisms in the KRTAP2-2 and KRTAP2-4 genes with distinct allele frequencies in Japanese and Caucasian populations. KRTAP2 proteins were predominantly expressed in the keratinizing zone of the hair shaft cortex and interacted with each other, binding preferentially to hair keratins. The research highlighted the essential role of KRTAP2 in hair shaft keratinization, providing insights into the evolution of KRTAP genes and their potential roles in hair disorders and cosmetic treatments. Various molecular biology techniques were used to analyze gene expression and protein interactions, contributing to the understanding of hair structure at the molecular level.