The gene encompasses 4.38 kb of gDNA.

Three alternative transcription start sites (TSSs) have been predicted or identified experimentally for the KLK4 gene. TSS1 was identified using 5 RACE and is located 639 bp upstream of TSS2, which was predicted using in silico analysis. TSS3 was also identified using 5 RACE and is located 1396 bp downstream of TSS1.
Nine KLK4 variant transcripts have been identified. These variants include the TSS variants, variants with 5 UTR deletion for TSS1 and TSS2 transcripts, exon 4 deletion and partial intron II (12bp) insertion variants, intron 3 insertion variants, and variants with combinations thereof.

Not identified.

Two KLK4 protein isoforms, full-length KLK4 (254 amino acids) and an N-terminal truncated KLK4 (205 amino acids) have been described. Full-length KLK4 has a secretion signal (pre-) peptide (26 amino acids), followed by an activation (pro-) peptide (4 amino acids) and the mature chain (224 amino acids) with 1 potential N-linked glycosylation site. The catalytic triad of His71, Asp116, Ser207 (relative to Met = 1 and encoded by ATG1 in exon 1) is conserved and is essential for proteolytic activity. After synthesis as a KLK4 full-length protein, the signal peptide is then cleaved and pro-KLK4 (zymogen) is subsequently secreted from the cell. Upon activation, the propeptide is removed to generate the mature active enzyme. KLK4 complexes with alpha(1)-antitrypsin and alpha(2)-antiplasmin and alpha(2)-macroglobulin.
The N-terminal truncated KLK4 isoform initiated from the ATG2 in exon 2, has the pre-pro-region and 9 amino acids from the mature KLK4 omitted, although the catalytic triad remains. Further, the truncated KLK4 isoform is not glycosylated despite retaining the potential N-linked glycosylation site.

The KLK4 gene was originally designated the PRSS17 gene and was cloned from the cells of the enamel organ epithelia of developing teeth in pig using degenerate primers encoding the EMPS1 protein. Subsequent studies in human tissues using Northern blot analysis have shown that KLK4 mRNA expression is predominantly localised to the prostate, although more sensitive RT-PCR experiments have shown that the breast, ovary, endometrium, salivary gland, lung, adrenal gland, colon, trachea, brain, testis, spinal cord, thyroid, skin and kidney also express KLK4 mRNA at low to modest levels. KLK4 mRNA has also been detected in sebaceous glands, sweat glands, hair follicles, stratum basale, stratum spinosum and stratum granulosum by in situ hybridisation experiments. In pig, KLK4 mRNA is expressed in the endometrium in the early stages of the oestrous cycle.
KLK4 protein has been detected in a wide range of tissues at low (adrenal, aorta, brain, breast, cervix, heart, kidney, liver, muscle, pancreas, pituitary, salivary gland, small intestine, spinal cord, spleen, testis, skin, thyroid, and uterus) to high (prostate) levels. Modest levels of KLK4 protein have also been detected in body fluid, such as seminal plasma and urine. High KLK4 levels have also been detected in the prostate, breast and ovarian cancer tissues from patients.

Full-length KLK4 encodes a secreted protein and is localised intracellularly to the cytoplasm, although GFP labelled N-terminal truncated isoforms have been found to be predominantly localised to the nucleus.

To date, the major biological function of KLK4 has been derived from porcine studies which have shown that KLK4 is important in dental enamel mineralisation by degrading amelogenin, the major protein in the enamel matrix of developing teeth. More recently, KLK4 was also reported to degrade porcine enamelin which is another protein found in developing teeth. Further, in mice, KLK4 was only expressed by transition and maturation stage ameloblasts, which is consistent with KLK4 functioning primarily to degrade the enamel matrix in developing teeth.
The role of KLK4 in the prostate, a tissue that highly expresses KLK4, is less clearly defined although it is thought to be important in prostate cancer progression given its role in degrading extracellular matrix (ECM) proteins in teeth, and potentially increasing IGF levels by degrading IGFBP3, IGFBP4, IGFBP5, IGFBP6. KLK4 is also reported to activate pro- HGFA and thereby potentially leading to tumour progression through activation of the MET receptor. A substrate specificity screening study has shown that full-length KLK4 has trypsin-like specificity and potentially activates proteins, such as, prostate specific antigen (PSA) / KLK3, bone morphogenetic protein (BMP) family and parathyroid hormone-related protein ( PTHrP ) that are involved in normal and neoplastic prostate (patho)-physiology. Recombinant KLK4 was also reported to be a better activator of PSA and single chain urokinase-type plasminogen activator than KLK2. More recently, KLK4 was shown to activate other members of the kallikrein-related peptidase family including KLK1, KLK2, KLK3, KLK5, KLK6, KLK9, KLK11, KLK12, KLK13, KLK14, KLK15. However, the precise physiological role for KLK4 in the prostate and other tissues remains to be identified. The function of the N-terminal truncated KLK4 remains to be established.

At the protein level, KLK4 shares 25%, (KLK12), 29% (KLK10), 31% (KLK9), 34% (KLK1, 2, 3), 35% (KLK8, 13), 36% (KLK6), 37% (KLK15), 40% (KLK14), 43% (KLK7), 45% (KLK5) sequence homology with other members of the kallikrein-related peptidase family. Unlike KLK1, KLK2 and KLK3, KLK4 lacks the "kallikrein loop", a region of 11 amino acids encoded in exon 3 and thought to be important in the substrate specificity of these enzymes. KLK4 shares 72% sequence homology to the porcine EMPS1 protein. Bayesian phylogenetic analyses suggests that KLK4, KLK5 and KLK14 may form a sub-family within the kallikrein-related peptidase gene family.

A mutation in the KLK4 gene (G.2142>A) that encodes for a truncated KLK4 protein that lacks S207, which is necessary for catalytic activity, has been shown to associate with autosomal recessive hypomaturation amelogenesis imperfecta, which is a disorder affecting tooth enamel formation. Comparison of tooth enamel in patients with the G- and A-alleles suggest that wild-type KLK4 (G allele) is important for the final removal of the extracellar enamel matrix proteins for normal enamel maturation.