Comparison of human and porcine tissue kallikrein substrate specificities

Proteolytic profiles of two isoforms of human AMBN expressed in E. coli by MMP-20 and KLK-4 proteases

Ameloblastin is a protein in biomineralization of tooth enamel. However recent results indicate that this is probably not its only role in an organism. Enamel matrix formation represents a complex process enabled via specific crosslinking of two proteins - the most abundant amelogenin and the ameloblastin (AMBN). The human AMBN (hAMBN) gene possesses 13 protein coding exons with alternatively spliced transcripts and the longest isoform about 447 amino acid residues. It has been described that AMBN molecules in vitro assemble into oligomers via a sequence encoded by exon 5. Enamel is formed by the processing of enamel proteins by two specific proteases - enamelysin (MMP-20) and kallikrein 4 (KLK-4). The scaffold made of AMEL and non-amelogenin proteins is cleaved and removed from the developed tooth enamel. The hAMBN is expressed in two isoforms (ISO I and II), which could lead to their different utilization determined by distinct proteolytic profiles. In this study, we compared proteolytic profiles of both isoforms of hAMBN expressed in E. coli after proteolysis by MMP-20, KLK-4, and their 1:2 mixture. Proteolysis products were analysed and cleavage sites were identified by mass spectrometry. The proteolytic profiles of two AMBN isoforms showed different results, although we have to determine that the analysed AMBN was not post-translationally modified as expressed in prokaryotic cells. These results may lead to the suggestion of potentially divergent roles of AMBN isoforms cleavage products in various cell signalling pathways such as calcium buffering or signalling cascades.

The use of Fluorescence Resonance Energy Transfer (FRET) peptidesfor measurement of clinically important proteolytic enzymes

Proteolytic enzymes have a fundamental role in many biological processes and are associated with multiple pathological conditions. Therefore, targeting these enzymes may be important for a better understanding of their function and development of therapeutic inhibitors. Fluorescence Resonance Energy Transfer (FRET) peptides are convenient tools for the study of peptidases specificity as they allow monitoring of the reaction on a continuous basis, providing a rapid method for the determination of enzymatic activity. Hydrolysis of a peptide bond between the donor/acceptor pair generates fluorescence that permits the measurement of the activity of nanomolar concentrations of the enzyme. The assays can be performed directly in a cuvette of the fluorimeter or adapted for determinations in a 96-well fluorescence plate reader. The synthesis of FRET peptides containing ortho-aminobenzoic acid (Abz) as fluorescent group and 2, 4-dinitrophenyl (Dnp) or N-(2, 4-dinitrophenyl)ethylenediamine (EDDnp) as quencher was optimized by our group and became an important line of research at the Department of Biophysics of the Federal University of São Paulo. Recently, Abz/Dnp FRET peptide libraries were developed allowing high-throughput screening of peptidases substrate specificity. This review presents the consolidation of our research activities undertaken between 1993 and 2008 on the synthesis of peptides and study of peptidases specificities.

Structure-guided design of peptidic ligand for human prostate specific antigen

Prostate specific antigen (PSA) is a member of kallikrein family having serine protease-like activity and acts as a prognostic marker of prostate carcinoma. Various studies have been performed on inhibition of PSA and such targeting requires the identification of highly selective peptide inhibitors. PSA was purified from human seminal plasma by rapid and efficient methods, and binding studies for various peptides were carried out by fluorescence spectroscopy and SPR. The 'S' of PSA is predominated by hydrophobic residues, and hence many hydrophobic peptides were used to determine their binding affinity to PSA by fluorescence spectroscopy. We observed that LLFW, FFKW, and KFW binds strongly to PSA, among them LLFW showed strong binding. SPR also showed strong binding affinity of PSA toward peptides with hydrophobic and basic residues. Among the peptides used, FWYS showed dramatic increase in binding affinity (10(-10) M). The peptides analyzed for binding studies, suggests that peptide with Trp residue along with basic or hydrophobic amino acids may be useful for designing specific inhibitors for PSA. The strong affinities of designed peptides for PSA can be a valuable tool for designing therapeutic agents for prostate carcinomas.

Enzymatic profiling of human kallikrein 14 using phage-display substrate technology

The humanKLK14gene is one of the newly identified serine protease genes belonging to the human kallikrein family, which contains 15 members.KLK14, like all other members of the human kallikrein family, is predicted to encode for a secreted serine protease already found in various biological fluids. This new kallikrein is mainly expressed in prostate and endocrine tissues, but its function is still unknown. Recent studies have demonstrated thatKLK14gene expression is up-regulated in prostate and breast cancer tissues, and that higher expression levels correlate with more aggressive tumors. In this work, we used phage-display substrate technology to study the substrate specificity of hK14. A phage-displayed random pentapeptide library with exhaustive diversity was screened with purified recombinant hK14. Highly specific and sensitive substrates were selected from the library. We show that hK14 has dual activity, trypsin- and chymotrypsin-like, with a preference for cleavage after arginine residues. A SwissProt database search with selected sequences identified six potential human protein substrates for hK14. Two of them, laminin α-5 and collagen IV, which are major components of the extracellular matrix, have been demonstrated to be hydrolyzed efficiently by hK14.

Differences in substrate and inhibitor sequence specificity of human, mouse and rat tissue kallikreins

The kininogenase activities of mouse (mK1), rat (rK1) and human (hK1) tissue kallikreins were assayed with the bradykinin-containing synthetic peptides Abz-MTEMARRPPGFSPFRSVTVQNH2 (where Abz stands for o-aminobenzoyl) and Abz-MTSVIRRPPGFSPFRAPRV-NH2, which correspond to fragments Met374-Gln393 and Met375-Val393 of mouse and rat LMWKs (low-molecular-mass kininogens) with the addition of Abz. Bradykinin was released from these peptides by the mK1- and rK1-mediated hydrolysis of Arg-Arg and Arg-Ser (or Arg-Ala) peptide bonds. However, owing to preferential hydrolysis of Phe-Arg compared with the Arg-Ala bond in the peptide derived from rat LMWK, hK1 released bradykinin only from the mouse LMWK fragment and preferentially released des-[Arg9]bradykinin from the rat LMWK fragment (Abz-MTSVIRRPPGFSPFRAPRV-NH2). The formation of these hydrolysis products was examined in more detail by determining the kinetic parameters for the hydrolysis of synthetic, internally quenched fluorescent peptides containing six N- or C-terminal amino acids of bradykinin added to the five downstream or upstream residues of mouse and rat kininogens respectively. One of these peptides, Abz-GFSPFRAPRVQ-EDDnp (where EDDnp stands for ethylenediamine 2,4-dinitrophenyl), was preferentially hydrolysed at the Phe-Arg bond, confirming the potential des-[Arg9]bradykinin-releasing activity of hK1 on rat kininogen. The proline residue that is two residues upstream of bradykinin in rat kininogen is, in part, responsible for this pattern of hydrolysis, since the peptide Abz-GFSPFRASRVQ-EDDnp was preferentially cleaved at the Arg-Ala bond by hK1. Since this peptidase accepts the arginine or phenylalanine residue at its S1 subsite, this preference seems to be determined by the prime site of the substrates. These findings also suggested that the effects observed in rats overexpressing hK1 should consider the activation of B1 receptors by des-[Arg9]bradykinin. For further comparison, two short internally quenched fluorescent peptides that bind to hK1 with affinity in the nM range and some inhibitors described previously for hK1 were also assayed with mK1 and rK1.

Identification of a novel apolipoprotein, ApoN, in ovarian follicular fluid

A novel apolipoprotein, designated ApoN, has been identified in bovine ovarian follicular fluid using chromatographic purification methods, amino acid sequence analysis, molecular biology, and bioinformatics. The apolipoprotein is a hydrophobic 12-kDa protein processed from the C terminus of a 29-kDa precursor expressed in a number of tissues, including the ovary, testis, the anterior chamber of the eye, skeletal muscle, uterus, and liver. Bovine, porcine, and murine ApoN display significant homology at the amino acid level across the entire precursor sequence. Surprisingly, there appears to be no orthologous protein in the human, although an APON-like pseudogene is found on chromosome 12. The N-terminal fragment of the ApoN precursor shows significant homology with the N-terminal sequence of the precursor of the cholesterol transport regulatory protein ApoF, but the corresponding C-terminal sequences of ApoN and ApoF possess no homology. ApoN is present in the high-density lipoprotein fraction of bovine serum and both the high-density lipoprotein and low-density lipoprotein fractions of bovine follicular fluid and is found in several tissues that are associated with local immunological privilege. These data suggest that ApoN may play a role in steroidogenesis and/or immunoregulation in the gonads of nonhuman species, as well as similar roles in other tissues.