Substrate Specificity of Human Kallikrein 6

Abstract

Human kallikrein 6 (hK6) is abundantly expressed in the central nervous system and is implicated in demyelinating disease. This study provided biochemical data about the substrate specificity and activation of hK6 by glycosaminoglycans and by kosmotropic salts, which followed the Hofmeister series. The screening of fluorescence resonance energy transfer (FRET) peptide families derived from Abz-KLRSSKQ-EDDnp resulted in the finding that Abz-AFRFSQ-EDDnp (where Abz is ortho-aminobenzoic acid and EDDnp is N-[2,4-dinitrophenyl]ethylenediamine)) is the best synthetic substrate described so far for hK6 (k cat /K m ‫؍‬ 38,667 s ؊1 mM ؊1 ). It is noteworthy that the AFRFS sequence was found as a motif in the amino-terminal domain of seven human ionotropic glutamate receptor subunits. We also examined the hK6 hydrolytic activity on FRET peptides derived from human myelin basic protein, precursor of the A␤ amyloid peptide, reactive center loop of ␣ 1 -antichymotrypsin, plasminogen, and maturation and inactivation cleavage sites of hK6, which were described earlier as natural substrates for hK6. The best substrates were derived from myelin basic protein. The hK6 maturation cleavage site was poorly hydrolyzed, and no evidence was found to support a two-step self-activation process reported previously. Finally, we assayed FRET peptides derived from sequences that span the cleavage sites for activation of protease-activated receptors (PAR) 1-4, and only the substrate with the PAR 2 sequence was hydrolyzed. These results further supported the hypothesis that hK6 expressed in the central nervous system is involved in normal myelin turnover/demyelination processes, but it is unlikely to self-activate. This report also suggested the possible modulation of ionotropic glutamate receptors and activation of PAR 2 by hK6.Human kallikreins (hK) 4 are a multigene family of 15 secreted serinetype proteases aligned in tandem on chromosome 19q13.4 (1-4) (the kallikrein genes are abbreviated as hKLK, mKLK, and rKLK, and the proteins as hK, mK, and rK depending on whether they are from human, mouse, or rat, respectively). Similarly, the mKLK and rKLK kallikrein gene families are composed of a large number of closely related members (5-9) that possibly arose from gene duplication events. The members of mouse, rat, and human kallikreins have a high degree of amino acid identity but present different substrate specificity, particularly toward oligopeptides (10 -17). The natural substrates and the substrate specificities of the kallikreins are known only for a few of them. hK1 is the best characterized kallikrein, it is a glycoprotein expressed most abundantly in pancreas, salivary gland, kidney, and urine (18), releases Lys-bradykinin by limited proteolysis from high and low molecular weight kininogens by cleavage at the Met 379 -Lys 380 and Arg 389 -Ser 390 bonds (19), and has both trypsin-and chymotrypsin-like activities (20 -23). hK2 is present in the seminal plasma, hydrolyzes certain components of the semen coagulum (24), and cleaves subst...

Proteinase-activated Receptors, Targets for Kallikrein Signaling

“…However, the actions of hK5 and -6 were distinct from those of hK14 in terms of their inability to activate PAR 4 . The lack of activation of PAR 4 by these two kallikreins is in keeping with the very minor cleavage by hK5 and -6 we observed by HPLC analysis for the PAR 4 -derived peptides and the lack of hydrolysis by hK6 of a model PAR 4 peptide described in work that appeared after completion of our study (56). We therefore anticipate that the other human kallikreins apart from hK5, -6, and -14 as well as kallikreins from other species will have both common and distinct actions via the different PARs.…”

Activation Profiles and Regulatory Cascades of the Human Kallikrein-related Peptidases

“…The hydrolysis of pro-KLK5 and -10 exhibits the greatest increase in response to acidic conditions (Tables 2 and 3), and because these KLKs are co-expressed with KLK6 in the CNS, we postulate that this response is of physiological relevance. The buffer conditions utilized in this study are unlikely to be optimal in each case, as studies have shown that salts and pH can have a substantial influence upon individual KLK activity and indeed may serve to regulate their activity (15,62).…”

Characterization of Trypanosoma cruzi Sirtuins as Possible Drug Targets for Chagas Disease

“…Deacetylase assays were performed at 37°C in 50 l of 25 mM Tris-HCl (pH 8.0), 137 mM NaCl, 2.7 mM KCl, 1 mM MgCl 2 containing 0.6 mM NAD ϩ (Sigma-Aldrich), and 20 M synthetic peptide Abz-Gly-Proacetyl-Lys-Ser-Gln-EDDnp, where Abz is ortho-aminobenzoic acid and EDDnp is N- [2,4-dinitrophenyl]ethylenediamine. The peptide was synthesized as described previously (31), further purified by chromatography on a C 18 column, dried, and resuspended in DMSO. A recombinant protein corresponding to the T. brucei RNA triphosphatase cloned in pET28a (32) was prepared similarly and used as a negative control, and a total HeLa cell extract was used as a positive control in the activity assays.…”