PubMed Health⌕ Search

Biomedical subjects

Boris Turk

Publications and source records attributed to Boris Turk.

29 records · Page 2Linked to original sources
PubMed2004

Comprehensive search for cysteine cathepsins in the human genome.

Our study was aimed at examinating whether or not the human genome encodes for previously unreported cysteine cathepsins. To this end, we used analyses of the genome sequence and mRNA expression levels. The program TBLASTN was employed to scan the draft sequence of the human genome for the 11 known cysteine cathepsins. The cathepsin-like segments in the genome were inspected, filtered, and annotated. In addition to the known cysteine cathepsins, the scan identified three pseudogenes, closely related to cathepsin L, on chromosome 10, as well as two remote homologs, tubulointerstitial protein antigen and tubulointerstitial protein antigen-related protein. No new members of the family were identified. mRNA expression profiles for 10 known human cysteine cathepsins showed varying expression levels in 46 different human tissues and cell lines. No expression of any of the three cathepsin L-like pseudogenes was found. Based on these results, it is likely that to date all human cysteine cathepsins are known.

Cathepsins↗
PubMed2004

Human cathepsin F: expression in baculovirus system, characterization and inhibition by protein inhibitors.

Recombinant full-length human procathepsin F, produced in the baculovirus expression system, was partially processed during the purification procedure to a form lacking the N-terminal cystatin-like domain and activated with pepsin. Active cathepsin F efficiently hydrolyzed Z-FR-MCA (kcat/Km=106 mM(-1) s(-1)) and Bz-FVR-MCA (kcat/Km=8 mM(-1) s(-1)), whereas hydrolysis of Z-RR-MCA was very slow (kcat/Km<0.2 mM(-1) s(-1)). Cathepsin F was rapidly and tightly inhibited by cystatin C, chicken cystatin and equistatin with Ki values in the subnanomolar range (0.03-0.47 nM), whereas L-kininogen was a less strong inhibitor of the enzyme (Ki=4.7 nM). Stefin A inhibited cathepsin F slowly (kass=1.6 x 10(5) M(-1) s(-1)) and with a lower affinity (Ki=25 nM). These data suggest that cathepsin F differs from other related endopeptidases by considerably weaker inhibition by stefins.

Animals↗
PubMed2003

Recombinant human cathepsin H lacking the mini chain is an endopeptidase.

Human procathepsin H was expressed in the form of inclusion bodies in Escherichia coli. Following refolding and autocatalytic activation, a recombinant cathepsin H form lacking the mini chain was produced. Removal of the mini chain completely abolished aminopeptidase activity of the enzyme and largely increased its endopeptidase activity (approximately 40-fold). Similarly to cathepsin S, Bz-FVR-AMC (k(cat)/K(m) value of 1070 mM(-1) s(-1)) was found to be the preferred substrate of recombinant cathepsin H. However, substrate inhibition was observed at a higher substrate (Z-FR-AMC, Bz-FVR-AMC) concentration. Endopeptidase activity of recombinant cathepsin H was seen also with the protein substrate insulin beta-chain with the major cleavage site between Glu13-Ala14. Recombinant human cathepsin H was inhibited by chicken cystatin, stefin A, and stefin B with the K(i) values in the range of 0.05-0.1 nM, which is slightly tighter than the inhibition of purified cathepsin H by the same inhibitors. These results thus indicate that the cathepsin H mini chain is essential for the aminopeptidase activity of the enzyme but has only a minor effect on the inhibition by cystatins.

Amino Acid Sequence↗
PubMed2003

Selective disruption of lysosomes in HeLa cells triggers apoptosis mediated by cleavage of Bid by multiple papain-like lysosomal cathepsins.

Increasing evidence suggests that lysosomal proteases are actively involved in apoptosis. Using HeLa cells as the model system, we show that selective lysosome disruption with L-leucyl-L-leucine methyl ester results in apoptosis, characterized by translocation of lysosomal proteases into the cytosol and by the cleavage of a proapoptotic Bcl-2-family member Bid. Apoptosis and Bid cleavage, but not translocation of lysosomal proteases to the cytosol, could be prevented by 15 microM L-trans-epoxysuccinyl(OEt)-Leu-3-methylbutylamide, an inhibitor of papain-like cysteine proteases. Incubation of cells with 15 microM N-benzoyloxycarbonyl-VAD-fluoromethyl ketone prevented apoptosis but not Bid cleavage, suggesting that cathepsin-mediated apoptosis in this system is caspase-dependent. In vitro experiments performed at neutral pH showed that papain-like cathepsins B, H, L, S, and K cleave Bid predominantly at Arg(65) or Arg(71). No Bid cleavage was observed with cathepsins C and X or the aspartic protease cathepsin D. Incubation of full-length Bid treated with cathepsins B, H, L, and S resulted in rapid cytochrome c release from isolated mitochondria. Thus, Bid may be an important mediator of apoptosis induced by lysosomal disruption.

Animals↗
PubMed2003

B cell receptor-mediated nuclear fragmentation proceeds in WEHI 231 cells in the absence of detectable DEVDase and FRase activity.

Crosslinking of the WEHI 231 lymphoma B cell receptor (BCR) leads to growth arrest followed by apoptosis. In a study of the role of lysosomal cysteine proteinases in BCR-mediated apoptosis we provide evidence that commitment to apoptosis correlates with a time-dependent increase in caspase and cathepsin activities. We also show that activation of cathepsins is a caspase-independent process, and caspase cascade activation is independent of lysosomal endopeptidases. BCR-induced nuclear fragmentation was not prevented, but rather delayed in the absence of detectable caspase and cathepsin activities, suggesting that BCR-driven apoptosis of these cells may use an alternative proteolytic mechanism independent of caspases and cathepsins.

Antibodies↗
PubMed2003

Papain-like lysosomal cysteine proteases and their inhibitors: drug discovery targets?

Papain-like lysosomal cysteine proteases are processive and digestive enzymes that are expressed in organisms from bacteria to humans. Increasing knowledge about the physiological and pathological roles of cysteine proteases is bringing them into the focus of drug discovery research. These proteases have rather short active-site clefts, comprising three well defined substrate-binding subsites (S2, S1 and S1') and additional broad binding areas (S4, S3, S2' and S3'). The geometry of the active site distinguishes cysteine proteases from other protease classes, such as serine and aspartic proteases, which have six and eight substrate-binding sites respectively. Exopeptidases (cathepsins B, C, H and X), in contrast with endopeptidases (such as cathepsins L, S, V and F), possess structural features that facilitate the binding of N- and C-terminal groups of substrates into the active-site cleft. Other than a clear preference for free chain termini in the case of exopeptidases, the substrate-binding sites exhibit no strict specificities. Instead, their subsite preferences arise more from the specific exclusion of substrate types. This presents a challenge for the design of inhibitors to target a specific cathepsin: only the cumulative effect of an assembly of inhibitor fragments will bring the desired result.

Amino Acid Sequence↗
PubMed2002

Regulating cysteine protease activity: essential role of protease inhibitors as guardians and regulators.

Cysteine proteases are widespread in nature. Their implication in numerous vital processes and pathologies make them highly attractive targets for drug design. The proper functioning and regulation of activity of cysteine proteases is a delicate balance of many factors, one of the most crucial being the protease inhibitors. In this review the basic principles of physiological protease inhibition by protein inhibitors are discussed with the focus on papain-like lysosomal cysteine proteases and the caspases, and their inhibitors.

Animals↗
PubMedDate not supplied

Lysosomal cysteine proteases: structural features and their role in apoptosis.

Among the variety of proteolytic enzymes enormous progress has been seen recently in our understanding of lysosomal cysteine proteases, also known as cysteine cathepsins. These enzymes play a crucial role in diverse biological processes in physiological and pathological states, including genetic diseases. In the present review, their properties and structural features that are important to an understanding of their biological function are presented. Special emphasis is given to the newly discovered role of lysosomal cathepsins in apoptotic pathways.

Animals↗
PubMedDate not supplied

Apoptotic pathways: involvement of lysosomal proteases.

Apoptosis or programmed cell death is the major mechanism used by multicellular organisms to remove infected, excessive and potentially dangerous cells. Cysteine proteases from the caspase family play a crucial role in the process. However, there is increasing evidence that lysosomal proteases are also involved in apoptosis. In this review various lysosomal proteases and their potential contribution to propagation of apoptosis are discussed.

Animals↗