The Effect of Cations on the Amidase Activity of Human Tissue Kallikrein: 1-Linear Competitive Inhibition by Sodium, Potassium, Calcium and Magnesium. 2-Linear Mixed Inhibition by Aluminium

Specificity studies on Kallikrein-related peptidase 7 (KLK7) and effects of osmolytes and glycosaminoglycans on its peptidase activity

KLK7 substrate specificity was evaluated by families of fluorescence resonance energy transfer (FRET) peptides derived from Abz-KLFSSK-Q-EDDnp (Abz=ortho-aminobenzoic acid and Q-EDDnp=glutaminyl-N-[2,4-dinitrophenyl] ethylenediamine), by one bead-one peptide FRET peptide library in PEGA resin, and by the FRET peptide libraries Abz-GXX-Z-XX-Q-EDDnp (Z and X are fixed and random natural amino acids, respectively). KLK7 hydrolyzed preferentially F, Y or M, and its S1' and S2' subsites showed selectivity for hydrophilic amino acids, particularly R and K. This set of specificities was confirmed by the efficient kininogenase activity of KLK7 on Abz-MISLM(↓)KRPPGFSPF(↓)RSSRI-NH2 ((↓)indicates cleavage), hydrolysis of somatostatin and substance P and inhibition by kallistatin. The peptide Abz-NLY(↓)RVE-Q-EDDnp is the best synthetic substrate so far described for KLK7 [kcat/Km=455 (mMs)(-1)] that was designed from the KLK7 substrate specificity analysis. It is noteworthy that the NLYRVE sequence is present in human semaphorin 6B. KLK7 is activated by GAGs, inhibited by neutral salts, and activated by high concentration of kosmotropic salt. Pyroglutamic acid inhibited KLK7 (Ki=33mM) and is present in skin moisturizing factor (124mM). The KLK7 specificity described here and elsewhere reflects its participation in patho-physiological events in skin, the gastrointestinal tract and central nervous system, where KLK7 is significantly expressed.

Expression and preliminary characterization of recombinant human tissue kallikrein in egg white of laying hens

Human tissue kallikrein (hK1) plays an important role in regulation of blood pressure, electrolyte and glucose transport, and renal function. To evaluate the feasibility of expression of recombinant human tissue kallikrein (rhK1) in the egg whites of laying hens, human tissue kallikrein gene (hKLK1) cDNA was subcloned into the chicken oviduct-specific expression vector (pOV3), and the resultant recombinant vector pOV3K was injected into laying hens via wing vein after mixing with polyethyleneimine. Following injection twice with the recombinant vector, the enzymatic activity at a maximal level of 59 U/mL was detected in the egg whites, which lasted for more than 7 d. The expression level of rhK1 in the egg whites in the 3-mg group was relatively higher than that in the 2-mg group, but the significant differences were identified on d 7 and 8 (P < 0.05). Ten days after the primary injection, the hens were reinjected with the same dose of the vector, and even higher enzymatic activity was detected in their egg whites. Two different breeds of hen were tested with no difference in expression level found (P > 0.05). Western blot analysis of the egg whites from vector-injected hens showed the rhK1 was recognized by a polyclonal antibody specific for hK1 with molecular weights of 37 and 43 kDa, which probably corresponded to the mature and preenzyme, respectively. Biochemical studies showed that the recombinant enzyme had a similar thermostability, optimal pH, hypotensive effect, and sensitivity to different ions to the natural enzymes in human and porcine tissues. These data indicate that the chicken oviduct-specific transient expression system can produce relatively high level and authentic recombinant enzyme with a potential for further development for therapeutic use.