Novel azapeptide inhibitors of cathepsins B and K. Structural background to increased specificity for cathepsin B

Abstract: We have designed and synthesized a new series of azapeptides which act as potential inhibitors of cathepsin B and/or cathepsin K. Their structures are based upon the inhibitory sites of natural cysteine protease inhibitors, cystatins. For the synthesized azapeptides, the equilibrium constants for dissociation of inhibitor–enzyme complex, K_i, were determined. Comparison of these values indicated that all of the azainhibitors act much stronger toward cathepsin B. Z‐Arg‐Leu‐His‐Agly‐Ile‐Val‐OMe ( 7 ) proved to be approximately 500 times more potent for cathepsin B than for cathepsin K. To be able to explain the obtained experimental values we used the molecular dynamics procedures to analyze the interactions between cathepsin B and compound 7 . We also determined the structure of the most potent and selective cathepsin B azainhibitor by means of NMR studies and theoretical calculations. In this report, we describe SAR studies of azapeptide inhibitors indicating the influence of the conformational flexibility of the examined compounds on inhibition of cathepsins B and K.     

Intracellular accumulation of the amyloidogenic L68Q variant of human cystatin C in NIH/3T3 cells.

AIM: To study the cellular transport of L68Q cystatin C, the cystatin variant causing amyloidosis and brain haemorrhage in patients suffering from hereditary cystatin C amyloid angiopathy (HCCAA). METHODS: Expression vectors for wild-type and L68Q cystatin C were constructed and used to transfect mouse NIH/3T3 cells. Stable cell clones were isolated after cotransfection with pSV2neo. Clones expressing human wild-type and L68Q cystatin C were compared with respect to secreted cystatin C by enzyme linked immunosorbent assay (ELISA), and for intracellular cystatin C by western blotting and immunofluorescence cytochemistry. Colocalisation studies in cells were performed by double staining with antibodies against human cystatin C and marker proteins for lysosomes, the Golgi apparatus, or the endoplasmic reticulum, and evaluated by confocal microscopy. RESULTS: Concentrations of human cystatin C secreted from transfected NIH/3T3 cells were similar to those secreted from human cells in culture. In general, clones expressing the gene encoding L68Q cystatin C secreted slightly lower amounts of the protein than clones expressing wild-type human cystatin C. Both immunofluorescence cytochemistry and western blotting experiments showed an increased accumulation of cystatin C in cells expressing the gene encoding L68Q cystatin C compared with cells expressing the gene for the wild-type protein. The intracellularly accumulating L68Q cystatin C was insoluble and located mainly in the endoplasmic reticulum. CONCLUSIONS: The cellular transport of human cystatin C is impeded by the pathogenic amino acid substitution Leu68-->Gln. The resulting intracellular accumulation and increased localised concentration of L68Q cystatin C might be an important event in the molecular pathophysiology of amyloid formation and brain haemorrhage in patients with HCCAA.     

Assessment of Resolution and Intercenter Reproducibility of Results of Genotyping Staphylococcus aureus by Pulsed-Field Gel Electrophoresis of SmaI Macrorestriction Fragments: a Multicenter Study

Twenty well-characterized isolates of methicillin-resistant Staphylococcus aureus were used to study the optimal resolution and interlaboratory reproducibility of pulsed-field gel electrophoresis (PFGE) of DNA macrorestriction fragments. Five identical isolates (one PFGE type), 5 isolates that produced related PFGE subtypes, and 10 isolates with unique PFGE patterns were analyzed blindly in 12 different laboratories by in-house protocols. In several laboratories a standardized PFGE protocol with a commercial kit was applied successfully as well. Eight of the centers correctly identified the genetic homogeneity of the identical isolates by both the in-house and standard protocols. Four of 12 laboratories failed to produce interpretable data by the standardized protocol, due to technical problems (primarily plug preparation). With the five related isolates, five of eight participants identified the same subtype interrelationships with both in-house and standard protocols. However, two participants identified multiple strain types in this group or classified some of the isolates as unrelated isolates rather than as subtypes. The remaining laboratory failed to distinguish differences between some of the related isolates by utilizing both the in-house and standardized protocols. There were large differences in the relative genome lengths of the isolates as calculated on the basis of the gel pictures. By visual inspection, the numbers of restriction fragments and overall banding pattern similarity in the three groups of isolates showed interlaboratory concordance, but centralized computer analysis of data from four laboratories yielded percent similarity values of only 85% for the group of identical isolates. The differences between the data sets obtained with in-house and standardized protocols could be the experimental parameters which differed with respect to the brand of equipment used, imaging software, running time (20 to 48 h), and pulsing conditions. In conclusion, it appears that the standardization of PFGE depends on controlling a variety of experimental intricacies, as is the case with other bacterial typing procedures.The use of electric field pulsing techniques in conjunction with agarose gel electrophoresis for discrimination of large DNA molecules was introduced by Schwarz and Cantor in 1984 (9). During the past decade the methodology has been adapted and improved by various research groups to the point that pulsed-field gel electrophoresis (PFGE) for bacterial strain typing is now utilized with relative ease in a variety of laboratories (1). The combination of contour-clamped homogeneous field electrophoresis and PFGE for the molecular analysis of Staphylococcus aureus has been reported since the late 1980s (7, 19). At present, PFGE is considered to have both the reproducibility and resolving power of a standard technique for the epidemiological typing of bacterial isolates (10, 15).Molecular typing systems can identify different strains within a species, generating data useful for taxonomic or epidemiologic purposes (10, 14). A frequently observed shortcoming of typing systems in general is their lack of reproducibility: most typing systems do not provide a definitive strain identification, which is usually due to the variability of the technique and the lack of large databases containing fragment patterns from a wide variety of organisms to which unknowns can be compared. These problems were recently described in detail for two molecular typing systems. A multicenter study on random amplification of polymorphic DNA for discrimination of S. aureus strains revealed a lack of interlaboratory reproducibility among the banding patterns generated by the participating centers, although the epidemiological interpretation of the data was similar for all the centers involved (16). For PFGE, a similar lack of interlaboratory reproducibility of patterns was observed, although the interpretation of the experimental data also differed per participating center (2). The latter study analyzed 12 different methicillin-resistant S. aureus (MRSA) strains with different techniques optimized in each center and different sources and types of equipment. Since interlaboratory discrepancies with respect to classification of the strains were observed, the study concluded that there is a clear need for standardization of the technique, including the construction of a panel of reference strains to assist the individual researcher in the optimization of the PFGE protocol.The aim of the present study was to compare the fragment patterns of a well-defined collection of MRSA isolates in 12 laboratories using in-house and a standard set of PFGE parameters to determine whether standardization of experimental parameters (DNA preparation and switching protocols) would improve intercenter reproducibility of PFGE analysis.     

Intra- and inter-species mobilisation of non-conjugative plasmids in staphylococci.

The ability of Staphylococcus aureus conjugative plasmids to mobilise non-conjugative resistance plasmids from clinical isolates of S. aureus and S. epidermidis was studied. Plasmids which could not be transferred by transduction or mixed-culture transfer were transferred from phage-typable and non-typable S. aureus and from S. epidermidis. Plasmids encoding single resistance determinants were transferred by mobilisation whereas multiple-resistance plasmids were transferred as co-integrates between the conjugative and non-conjugative plasmids. This study demonstrates that mobilisation is a useful tool for the transfer and study of staphylococcal plasmids and illustrates how antibiotic resistance could be transferred between staphylococci in vivo.     

Gm allotypes in IgA deficiency

Gm phenotypes were examined in 90 Swedish IgA-deficient (less than 0.05 g/litre of serum IgA) donors and 40 normal first and second degree relatives of six of these donors. The G1m1,2, G3m5 and Km1 frequency in the group of IgA-deficient donors did not differ from that found in the normal population. Among the relatives, HLA and/or Gm identical normal sibs were observed. Anti-IgA antibodies were present in 29 of the IgA-deficient donors and anti-IgG in seven. No association between the two was found. A statistically significant association between the G1m-2 phenotype and the presence of anti-IgA antibodies was observed. When subdivided according to HLA type, a non-random distribution of Gm phenotypes was seen in HLA-B8/DR3 positive individuals with anti-IgA antibodies (HLA-B8/DR3 being the haplotype associated with IgA deficiency). These data suggest an association between IgA deficiency, anti-IgA and the studied Gm allotypes.     

Cerebral blood flow in birds: effect of hypoxia.

The effect of hypoxia on cerebral blood flow in ducks was investigated by the rate at which arterially injected xenon-133 was cleared from the duck's brain. A two-component clearance curve resulted, which we have attributed to flow through the grey and white matter. Decreasing the arterial oxygen tension (PaO2) to 75 mmHg had no effect on cerebral blood flow. However, decreasing the PaO2 below 75 mmHg significantly increased blood flow to the fast-clearing compartment. The greatest increase in blood flow was seen when the arterial PO2 was below 50 mmHg. At an arterial PO2 of 30 mmHg, the cerebral blood flow to the fast-clearing compartment was increased more than 600% above the normoxic level. The magnitude of this increase is much greater in the duck than has been reported for mammals at roughly equivalent arterial oxygen tensions. The ability of avian cerebral blood flow to increase at moderate levels of hypoxia, plus the magnitude of the increase, may play a role in the exceptional tolerance of birds to hypoxia.