Development of a non-radioactive, 384-well format assay to detect inhibitors of the mitogen-activated protein kinase kinase 4.

Mitogen-activated protein kinase (MAPK) kinases (MKKs, also called MAPK/extracellular signal-regulated kinase [ERK] kinase [MEK]) are constituents of numerous signal transduction pathways involved in growth, differentiation, and stress response. One of its members, MKK4, directly phosphorylates and activates the c-Jun terminal kinases (also called stress-activated protein kinase [SAPK]) in response to stress and pro-inflammatory cytokines. Recent evidence suggest that control of MKK4 activity may provide a novel approach for the treatment of cancer or as anti-inflammatory therapy. To screen for novel low-molecular-weight inhibitors of MKK4, we established a quantitative, non-radioactive in vitro kinase assay. Human MKK4 was expressed as fusion protein with glutathione S-transferase (GST) in Escherichia coli. Co-expression of a constitutive active fragment of the MAPK/ERK kinase kinase-1 yielded active GST-MKK4 using GST-SAPK alpha-kinase-negative (KN) mutant as substrate. We determined the kinetic constants for ATP and GST-SAPK alpha-KN. The apparent Km value for GST-SAPKalpha-KN was 3.7 microM, while the apparent Km value for ATP was 0.17 microM. Staurosporine inhibited GST-MKK4 with an IC50 of 70 nM. The kinase assay was adapted to a 384-well non-radioactive format. After the kinase reaction the phosphorylated product was captured onto a streptavidin-coated microtiter plate, and phosphorylation was detected with a europium-labeled anti-phosphotyrosine antibody, which allowed time-resolved fluorescence measurement.

Directed evolution to improve the thermostability of prolyl endopeptidase.

Prolyl endopeptidase is the only endopeptidase that specifically cleaves peptides at proline residues. Although this unique specificity is advantageous for application in protein chemistry, the stability of the enzyme is lower than those of commonly used peptidases such as subtilisin and trypsin. Therefore, we attempted to apply a directed evolution system to improve the thermostability of the enzyme. First, an efficient expression system for the enzyme in Escherichia coli was established using the prolyl endopeptidase gene from Flavobacterium meningosepticum. Then, a method for screening thermostable variants was developed by combining heat treatment with active staining on membrane filters. Random mutagenesis by error-prone PCR and screening was repeated three times, and as a result the thermostability of the enzyme was increased step by step as the amino acid substitutions accumulated. The most thermostable mutant obtained after the third cycle, PEP-407, showed a half-life of 42 min at 60 degrees C, which was 60 times longer than that of the wild-type enzyme. The thermostable mutant was also more stable with a high concentration of glycerol, which is a necessary condition for in vitro amidation.

Conformational studies on the specific cleavage site of Type I collagen (alpha-1) fragment (157-192) by cathepsins K and L by proton NMR spectroscopy.

Cathepsins K and L are cysteine proteinases which are considered to play an important role in bone resorption. Type I collagen is the most abundant component of the extracellular matrix of bone and regarded as an endogenous substrate for the cysteine proteinases in osteoclastic bone resorption. We have synthesized a fragment of Type I collagen (alpha-1) (157-192) as a substrate for the cathepsins and found that cathepsins K and L cleave the fragment at different specific sites. The major cleavage sites for cathepsin K were Met159-Gly160, Ser162-Gly163 and Arg165-Gly166, while those for cathepsin L were Gly166-Leu167 and Gln180-Gly181. The structure of the fragment was analyzed in aqueous solution by circular dichroism and proton NMR spectroscopy and the difference in the molecular recognition of collagen by cathepsins K and L was discussed from the structural aspect.

Some pharmacological properties of a newly synthesized morphine derivative, (-)-6 beta-acetylthiomorphine.

Some pharmacological properties of a newly synthesized morphine derivative, (-)-6 beta-acetylthiomorphine (AcS-morphine) were studied. AcS-morphine was about twice as potent as morphine in the inhibitory action of the twitch response of the guinea-pig ileal preparation to electrical stimulation. AcS-morphine, however, was 5 times as potent as morphine in the analgesic action in the rats. Both the effects of AcS-morphine were inhibited by naloxone, suggesting that the site of action of AcS-morphine is mu-receptors. It is interesting that 6 beta-isomer of AcS-morphine is 5 times as potent as 6 alpha-OH isomer of morphine in the analgesic action, because 6 alpha-OH isomer of morphine is much more potent than that of 6 beta-OH isomer. The effects of AcS-morphine on the specific binding of [3H]-naloxone, [3H]-ethylketocyclazocine and [3H]-D-Ala2-D-Leu5-enkephalin to the membrane fractions from the rat brain were tested. AcS-morphine was about 5 times as potent as morphine in its interactions with opioid receptors, as determined by the binding assay. AcS-morphine, as well as morphine, had a selectively high affinity to mu-receptors. The "sodium effect" and the "GTP effect" of AcS-morphine were almost the same as those of morphine. The dependence liability of AcS-morphine was preliminary tested in the guinea-pig ileal preparations treated with a high concentration of AcS-morphine for 24 hr. Results suggested that AcS-morphine is weaker than morphine in its dependence liability, though it seems almost certain that AcS-morphine does have this liability.