A 33-kD glycoprotein, known as the "prostate-specific antigen," was purified to homogeneity from human seminal plasma. The prostatic protein was identified as a serine protease, and its NH2-terminal sequence strongly suggests that it belongs to the family of glandular kallikreins. The structural protein of human seminal coagulum, the predominant protein in seminal vesicle secretion, was rapidly cleaved by the prostatic enzyme, which suggests that this seminal vesicle protein may serve as the physiological substrate for the protease. The prostatic enzyme hydrolyzed arginine- and lysine-containing substrates with a distinct preference for the former. All synthetic substrates tested were poor substrates for the enzyme. Synthetic Factor XIa substrate (pyro-glutamyl-prolyl-arginine-p-nitroanilide), and the synthetic kallikrein substrate (H-D-prolyl-phenylalanyl-arginine-p-nitroanilide) were hydrolyzed with maximum specific activities at 23 degrees C of 79 and 34 nmol/min per mg and Km values of 1.0 and 0.45 mM, respectively. Synthetic substrates for plasmin, chymotrypsin, and elastase were either not hydrolyzed by the enzyme at all, or only hydrolyzed very slowly.

/pdf/a-kallikrein-like-serine-protease-in-prostatic-fluid-cleaves-4xkuhbhwun.pdf

A kallikrein-like serine protease in prostatic fluid cleaves the predominant seminal vesicle protein.

Snake venom proteases affecting hemostasis and thrombosis.

The glandular kallikrein gene family comprises 25–30 highly homologous genes that encode specific proteases involved in the processing of biologically active peptides. In the mouse all the members of this family are closely linked on chromosome 7. The 9.5-kilobase nucleotide sequence of a mouse genomic clone contains one complete kallikrein gene (mGK-1), which is expressed in the male mouse submaxillary gland, and the 3′ end of another (mGK-2). Differences in the coding potential of these genes and the amino acid sequences of other known kallikreins seem to be functionally related to the substrate specificity of the different enzymes.

Structure of mouse kallikrein gene family suggests a role in specific processing of biologically active peptides.

The 15 members of the kallikrein-related serine peptidase (KLK) family have diverse tissue-specific expression profiles and putative proteolytic functions. The kallikrein family is also emerging as a rich source of disease biomarkers with KLK3, commonly known as prostate-specific antigen, being the current serum biomarker for prostate cancer. The kallikrein locus is also notable because it is extraordinarily responsive to steroids and other hormones. Indeed, at least 14 functional hormone response elements have been identified in the kallikrein locus. A more comprehensive understanding of the transcriptional regulation of kallikreins may help the field make more informed hypotheses about the physiological functions of kallikreins and their effectiveness as biomarkers. In this review, we describe the organization of the kallikrein locus and the structure of kallikrein genes and proteins. We also focus on the transcriptional regulation of kallikreins by androgens, progestins, glucocorticoids, mineralocorticoids, estrogens, and other hormones in animal models and human prostate, breast, and reproductive tract tissues. The interaction of the androgen receptor with androgen response elements in the promoter and enhancer of KLK2 and KLK3 is also summarized in detail. There is evidence that all kallikreins are regulated by multiple nuclear receptors. Yet, apart from KLK2 and KLK3, it is not clear whether all kallikreins are direct transcriptional targets. Therefore, we argue that gaining more detailed information about the mechanisms that regulate kallikrein expression should be a priority of future studies and that the kallikreinlocuswillcontinuetobeanimportantmodelintheeraofgenome-wideanalyses.(EndocrineReviews 31: 407–446, 2010)

/pdf/kallikreins-on-steroids-structure-function-and-hormonal-1njud0ijm4.pdf

Kallikreins on steroids: structure, function, and hormonal regulation of prostate-specific antigen and the extended kallikrein locus.

We have determined the nucleotide sequence of four submaxillary gland mRNAs, designated PS, S1, S2, and S3, that encode kallikrein and kallikrein-like serine proteases. The four enzymes share between 74% and 86% amino acid sequence identity and are identical in length with the exception of single two amino acid deletions in the S2 and S3 enzymes. The PS enzyme appears to be a true tissue kallikrein. The S1 enzyme shares 86% amino acid sequence homology with the PS enzyme and retains key amino acid residues thought to be primary determinants of kallikrein cleavage specificity. The S2 enzyme is rat submaxillary tonin. The amino acid sequence of the S3 enzyme is identical with tonin at 84% of its amino acid positions and retains the same amino acid substitutions at positions likely to determine substrate cleavage preferences.

Kallikrein-related mRNAs of the rat submaxillary gland: nucleotide sequences of four distinct types including tonin.

The amino acid sequence of the A- and B-chains of porcine pancreatic kallikrein B is presented and compared to that of porcine trypsin. The overall homology between both enzymes is 37% identical residues in corresponding position and 51% chemically similar residues. Comparison of the sequences with the crystal structure of bovine trypsin reveals that the trypsin “autolysis loop” is enlarged in kallikrein by two residues but lacks the basic residue at the cleavage site. Substitutions at the calcium-binding site of trypsin which include Arg 70 for Glu 70 possibly interfere with ion binding. Insertions between trypsin residues 95 and 96 obviously form a new kallikrein “autolysis loop” containing the site of cleavage between the A- and B-chains. One carbohydrate moiety is attached to this surface loop at Asn 95, the second to Asn 239 at the same edge of the globular molecule. The residues at the surface of the substrate binding site are substituted to an extent of 85% while the residues forming contacts to the trypsin inhibitor (Kunitz) are highly preserved. Immunodiffusion studies as well as identity of the N-terminal sequences of pancreatic, submandibular and urinary kallikrein reveal the same genetic origin of the three glandular kallikreins.

The Primary Structure of Porcine Glandular Kallikreins

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The Primary Structure of Porcine Glandular Kallikreins