KRTAP1-5 (keratin-associated protein 1-5) is a hair structural protein that functions primarily in hair shaft formation and mechanical properties. In the hair cortex, KRTAP1-5 embeds within the interfilamentous matrix surrounding keratin intermediate filaments, where it cross-links with cysteine-rich hair keratins through extensive disulfide bonding to create a rigid and resistant hair structure 1. KRTAP1-5 belongs to the keratin-associated protein 1 family, characterized by cysteine-containing pentapeptide repeats in its repetitive domains that facilitate these cross-linking interactions 1. The gene is located within a 600-kb cluster of keratin and KAP genes on chromosome 17-21 2, and notably shows no polymorphic alleles in population studies, suggesting structural conservation 3. Beyond hair biology, KRTAP1-5 expression has been identified as a gene signature in therapeutically effective human nasal turbinate-derived stem cells (hNTSCs) used to treat rheumatoid arthritis in murine models 4. Additionally, KRTAP1-5 is upregulated during keratin intermediate filament formation in mesenchymal stem cells following actin cytoskeleton perturbation 5 and is differentially expressed in gingival stem/progenitor cells under inflammatory and nutrient supplementation conditions 6. These findings suggest KRTAP1-5 may have broader roles in stem cell biology and tissue regeneration beyond its canonical hair structural functions.