Characterization of human KAP24.1, a cuticular hair keratin-associated protein with unusual amino-acid composition and repeat structure

In a search for genes overexpressed in human sexual hairs, several partial complementary DNA (cDNA) sequences were isolated. Screening of a human scalp cDNA library with one fragment led to the isolation of a full-length cDNA clone, which showed identity to another known sequence, termed KAP24-1 (AB09693). Bioinformatic analysis revealed that the gene for this cDNA consisted of one exon and was located ca. 86 kb away from the chromosome 21q22.1 keratin-associated protein (KAP) gene domain. RT-PCR analysis of a variety of organs showed that KAP24.1 was only present in human scalp. The KAP24.1 protein consisted of 254 amino acids, exhibited a high content of serine, proline, and tyrosine, but low cysteine content and possessed several carboxyterminal tyrosine-containing tandem decameric repeat structures. Evolutionary tree analysis showed no association to other KAP family members. In situ hybridization and indirect immunofluorescence microscopy studies using an antibody derived from KAP24.1 demonstrated specific expression in the middle/upper hair cuticle. The structure of the KRTAP24, its proximity to the chromosome 21q22.1 KAP gene domain, the presence of repeat motifs in the protein and its localization in the hair cuticle points to KAP24.1 being a novel human KAP family member.