Kallikrein 5/KLK5 Protein, Human, Recombinant (His) is expressed in HEK293 mammalian cells with C-6xHis tag. The predicted molecular weight is 40 KDa and the accession number is Q9Y337.

Kallikrein-4, also known as Enamel matrix serine proteinase 1, Kallikrein-like protein 1, KLK-L1, Serine protease 17, KLK4, PRSS17, and EMSP1, is a secreted protein that belongs to the peptidase S1 family and Kallikrein subfamily. Kallikrein-4 / KLK4 is a serine protease expressed during enamel maturation, and proteolytic processing of the enamel matrix by KLK4 is critical for proper enamel formation. Kallikrein-4 / KLK4 contains one peptidase S1 domain. Kallikrein-4 / KLK4 is secreted by transition- and maturation-stage ameloblasts. KLK4 aggressively degrades the retained organic matrix following the termination of enamel protein secretion. Two proteases are secreted into the enamel matrix of developing teeth. The early protease is enamelysin (MMP-2). The late protease is kallikrein 4 (KLK4). The principal functions of MMP-2 and KLK4 in dental enamel formation are to facilitate the orderly replacement of organic matrix with mineral, generating an enamel layer that is harder, less porous, and unstained by retained enamel proteins. Defects in Kallikrein-4 / KLK4 are the cause of Amelogenesis Imperfecta Hypomaturation type 2A1 (AI2A1) which is an autosomal recessive defect of enamel formation. The disorder involves both primary and secondary dentitions.

Kallikrein-2 (KLK2) is a secreted serine protease that belongs to the peptidase S1 family of Kallikrein subfamily. KLK2 contains 1 peptidase S1 domain. It is highly expressed in the human prostate gland. KLK2 can cleave Met-Lys and Arg-Ser bonds in kininogen to release Lys-bradykinin, but Preferential cleavages of Arg-|-Xaa bonds in small molecule substrates. It also highly selective action to release kallidin (lysyl-bradykinin) from kininogen involves hydrolysis of Met-|-Xaa or Leu-|-Xaa. KLK2 is inhibited by serpins such as protein C inhibitor, antichymotrypsin, and plasminogen. KLK2 is considered to be a biomarker for prostate cancer.

The inhibition of kallikrein 5 (KLK5) has been identified as a potential strategy for treatment of the genetic skin disorder Netherton syndrome, in which loss-of-function mutations in the SPINK5 gene lead to down-regulation of the endogenous inhibitor LEKTI-1 and profound skin-barrier defects with severe allergic manifestations. To aid in the development of a medicine for this target, an X-ray crystallographic system was developed to facilitate fragment-guided chemistry and knowledge-based drug-discovery approaches.