Cynomolgus monkey (Macaca fascicularis) cathepsin K: cloning, expression, purification, and activation.

Methodology for the production of recombinant active cynomolgus monkey (Macaca fascicularis) cathepsin K (EC 3.4.22.38) was elucidated. The cDNA encoding the cathepsin K was cloned from female M. cynomolgus monkey mRNA. The deduced amino acid sequence of M. cynomolgus preprocathepsin K from the cDNA sequence showed 94.2% identity to human preprocathepsin K. Sequence differences occurred only in the prepro- domains; the mature domains were identical. The recombinant M. cynomolgus cathepsin K was expressed as a secreted proenzyme using baculovirus-infected SF21 insect cells having the predicted N-terminus (LYPEEILDTH ellipsis ), indicating proper cleavage of the secretion sequence. Purified monkey procathepsin K was activated under autocatalytic conditions at pH 4.0. The mature enzyme was composed of mixture of enzymes having N-termini of Gly113 and Arg114. The molecular weight was determined to be 23,668.3 Da by MALDI-TOF-MS which is consistent with the absence of carbohydrate on the mature enzyme. These results indicate that monkey procathepsin K is able to autoactivate and produces a mature enzyme which is identical to that of human cathepsin K. Since the sequence of monkey and human mature cathepsin K are identical and the in vitro activation mechanisms appear to be indistinguishable, monkeys are predicted to be a good animal model for evaluating cathepsin K inhibitors in vivo as therapeutic agents for diseases characterized by excessive bone loss, such as osteoporosis.

Autocatalytic activation of human cathepsin K.

The in vitro activation of the recombinant purified human cathepsin K (EC 3.4.22.38) was examined by mutagenesis. Cathepsin K was expressed as a secreted proenzyme using baculovirus-infected Sf21 insect cells. Spontaneous in vitro activation of procathepsin K occurred at pH 4 and was catalyzed by exogenous mature cathepsin K. Three intermediates were identified as resulting from cleavages after Glu19, Ser98, and Glu110. The mature enzyme was composed of mixture of enzymes with N termini of Gly113, Arg114, and Ala115 with varying ratios depending on the preparation. Molecular weight determinations were consistent with the absence of carbohydrate in the mature protein, while electrospray mass spectroscopy indicated that six of the eight cysteine residues were in disulfide linkage, and that the protein had Met329 as the C-terminal residue. A mutant was constructed in which the active site Cys139 was changed to Ser. [Ser139,Ala163]Procathepsin K (containing mutation C139S,S163A) failed to spontaneously process and was only partially processed in the presence of 1% exogenous wild-type mature cathepsin K forming intermediates, which were identical to those observed in the activation of wild-type. [Ser139,Ala163]Procathepsin K could be fully processed to mature enzyme by including one equivalent of wild-type procathepsin K in the activation mixture. These results indicated that in vitro activation of the procathepsin K was an autocatalytic process.

Design of potent and selective human cathepsin K inhibitors that span the active site.

Potent and selective active-site-spanning inhibitors have been designed for cathepsin K, a cysteine protease unique to osteoclasts. They act by mechanisms that involve tight binding intermediates, potentially on a hydrolytic pathway. X-ray crystallographic, MS, NMR spectroscopic, and kinetic studies of the mechanisms of inhibition indicate that different intermediates or transition states are being represented that are dependent on the conditions of measurement and the specific groups flanking the carbonyl in the inhibitor. The species observed crystallographically are most consistent with tetrahedral intermediates that may be close approximations of those that occur during substrate hydrolysis. Initial kinetic studies suggest the possibility of irreversible and reversible active-site modification. Representative inhibitors have demonstrated antiresorptive activity both in vitro and in vivo and therefore are promising leads for therapeutic agents for the treatment of osteoporosis. Expansion of these inhibitor concepts can be envisioned for the many other cysteine proteases implicated for therapeutic intervention.

Production of biologically active human RelA (p65) in baculovirus-infected insect cells.

A recombinant baculovirus was constructed to express a cDNA encoding RelA (p65), a member of the NF-kappa B/Rel family of proteins. Infection of Spodoptera frugiderda insect cells with the recombinant baculovirus resulted in the production of the biologically active protein as measured by immunoblotting using RelA-specific antisera and by electrophoretic mobility shift assays. The recombinant protein bound specifically to an oligonucleotide containing the NF-kappa B consensus motif but not to that containing the unrelated Oct-1 consensus motif. Thus insect cell-derived RelA possess properties similar to the native protein and may be used in physical, biochemical, and pharmacological studies.

Proteolytic activity of human osteoclast cathepsin K. Expression, purification, activation, and substrate identification.

Human cathepsin K is a recently identified protein with high primary sequence homology to members of the papain cysteine protease superfamily including cathepsins S, L, and B and is selectively expressed in osteoclasts (Drake, F.H., Dodds, R., James I., Connor J., Debouck, C., Richardson, S., Lee, E., Rieman, D., Barthlow, R., Hastings, G., and Gowen, M. (1996) J. Biol., Chem. 271, 12511-12516). To characterize its catalytic properties, cathepsin K has been expressed in baculovirus-infected SF21 cells and the soluble recombinant protein isolated from growth media was purified. Purified protein includes an inhibitory pro-leader sequence common to this family of protease. Conditions for enzyme activation upon removal of the pro-sequence have been identified. Fluorogenic peptides have been identified as substrates for mature cathepsin K. In addition, two protein components of bone matrix, collagen and osteonectin, have been shown to be substrates of the activated protease. Cathepsin K is inhibited by E-64 and leupeptin, but not for by pepstatin, EDTA, phenylmethylsulfonyl fluoride, or phenanthroline, consistent with its classification within the cysteine protease class. Leupeptin has been characterized as a slow binding inhibitor of cathepsin K (kobs/[I] = 273,000 m(-1).s(-1)). Cathepsin K may represent the elusive protease implicated in degradation of protein matrix during bone resorption and represents a novel molecular target in treatment of disease states associated with excessive bone loss such as osteoporosis.

Characterization of two human cAMP-specific phosphodiesterase subtypes expressed in baculovirus-infected insect cells.

Recombinant baculoviruses were constructed to express cDNAs encoding two distinct subtypes of human cAMP-specific phosphodiesterase (hPDE4A and hPDE4B). Infection of Spodoptera frugiperda insect cells with the appropriate recombinant baculoviruses resulted in high level production of biologically-active protein as measured by enzymatic activity and immunoblotting using subtype-specific anti-hPDE4 antisera. Both recombinant proteins showed catalytic activity with a low Km (approximately 3 microM) for cAMP (with no cGMP hydrolyzing activity) and were inhibited by R-rolipram with apparent Kis of 0.38 and 0.25 microM, respectively. The recombinant enzymes also contained saturable, stereoselective and high-affinity rolipram-binding sites (Kd approximately 2 nM). Thus, insect cell-derived hPDE4s possess kinetic properties analogous to native enzymes as well as to recombinant enzymes produced in yeast.