The D8D9 fragment of SPINK5 (Serine protease inhibitor Kazal-type 5, also known as LEKTI, Lympho-epithelial Kazal-type-related inhibitor), consisting of residues 490 - 624 of the full-length protein, binds to KLK5 (Kallikrein-5), inactivating the latter. At neutral pH, complex formation is effectively irreversible. In normal skin, this event occurs extracellularly in the stratum corneum of the skin. As the complex is carried into layers nearer the surface of the skin, falling pH triggers its dissociation and release of active KLK5. Mutations that inactivate SPINK5 are associated with a severe skin disorder, Netherton syndrome (NS, MIM 256500), whose symptoms include premature desquamation (Deraison et al, 2007; Fortugno et al. 2011). Consistent with the hypothesis that SPINK5-mediated inhibition of KLK5 activity is a key feature of regulating normal desquamation, the NS-like phenotype of mice whose SPINK5-homologous gene has been knocked out is reversed in mice missing both SPINK5 and KLK5 activitiies (Furio et al. 2015).