Hair keratin–associated proteins (K

Hair keratin–associated proteins (KRTAPs) are one of the major structural components of the hair shaft.Approximately 100 KRTAP genes have been identified in humans to date, with each of the genes classified into anumber of families based on their sequence homology and the nature of the repeat structures. The biophysicalfeatures of KRTAPs, however, have remained largely unknown. In this study, we investigated the characteristicsof the human KRTAP2 family members at the DNA, RNA, and protein levels. We initially found that these geneshad various size polymorphisms that were mainly due to differences in the length of the 30-noncodingsequences. Reverse transcriptase–PCR experiments further detected the presence of KRTAP2 transcripts inplucked human hairs. Using indirect immunofluorescence with an anti-KRTAP2 antibody, we found that therewas a predominant expression of the KRTAP2 proteins in the keratinizing zone of the human hair shaft cortex. Inaddition, we showed that the KRTAP2 proteins interacted with each other and preferentially bound to hairkeratins, but not to epithelial keratins. Finally, we determined that the head domain of the hair keratins wasessential for the affinity to KRTAP2 proteins. Our results further enhance the crucial roles of KRTAPs in hair shaftkeratinization in humans.