Human Kallikreins: Common Structural Features, Sequence Analysis and Evolution

Kallikreins are a subgroup of serine proteases with diverse physiological functions. The human kallikrein gene family has now been fully characterized and includes 15 members tandemly located on chromosome 19q13.4 In this review, we discuss the common structural features of kallikreins at the DNA, mRNA and protein levels and summarize their tissue expression and hormonal regulation. Kallikreins are expressed in a wide range of tissues including the salivary gland, endocrine tissues including testis, prostate, breast, endometrium, and the central nervous system. Most, if not all genes are under steroid hormone regulation. The classical kallikreins (KLK1-3) are thought to represent a distinct evolutionary subgroup of kallikreins. The occurrence of several splice variants is a very common phenomenon among kallikreins, and some of the splice variants appear to be tissue-specific and might be related to certain pathological conditions. We also provide a summary of predicted and experimentally confirmed promoter elements of kallikrein genes and describe repeat elements and polymorphisms within this genomic region.