Action of rennet and other proteolytic enzymes on casein in casein-agar gels

Structure of intact chitinase with hevein domain from the plant Simarouba glauca, known for its traditional anti-inflammatory efficacy

Chitinase from the leaves of Simarouba glauca, a plant used in traditional anti-inflammatory therapy is purified and characterized. Peptide mass finger print analysis revealed the protein as an endo-chitinase which was further confirmed using chitin-agar assay. The enzyme exhibited significant anti-fungal efficacy against phyto-pathogens such as Macrophomina phaseolina, Fusarium oxysporum and Sclerotium rolfsii. Chitinolysis was also examined against insoluble chitin using SEM. Using X-ray diffraction data up to 1.66 Å, the structure was determined by Molecular Replacement using crystal structure of GH19 Chitinase-like protein from Hevea brasiliensis. During structure refinement, an extra domain could be traced and identified as hevein domain. To our knowledge, this is the first report of any chitinase with intact hevein domain. The GH19 chitinase and hevein domains though connected by a lengthy loop, are restricted to be close by disulfide bridges. These bridges connecting each domain with the loop may be important for proper chitin feeding into the active site. By considering reports on hevein and chitinase domains as well as the traditional use of the plant, this report of an intact hevein-chitinase protein and their relative orientation may add further insights for the usefulness of this protein.

Structural insights into a multifunctional inhibitor, 'AMTIN' from tubers of Alocasia macrorrhizos and its possible role in dengue protease (NS2B-NS3) inhibition

Protease inhibitors from plants play major role in defensive mechanism against various pathogenic organisms. AMTIN from the tubers of Alocasia macrorrhiza has been purified and characterized as multi-functional Kunitz type protease inhibitor. AMTIN is varied from other KTIs by having three different loops specific for binding to trypsin/amylase and subtilisin that are located approximately 30Ǻ away from one another as evidenced from crystallographic efforts. Biochemical studies on AMTIN reveal simultaneous binding of protease/amylase and have been cross validated using in-silico tools to model Amylase - AMTIN - Trypsin complex without any steric clashes. Apart from multi functionality, the remarkable structural and functional stability of AMTIN at high temperature, presence of many phosphorylation, myristoylation and glycosylation sites and molecular docking studies with dengue viral protease (NS2B-NS3) makes this protein interesting. Hence AMTIN can be considered as a template to design effective antivirals against dengue virus.

A structural biology approach to understand human lymphatic filarial infection

The presence of aspartic protease inhibitor in filarial parasite Brugia malayi (Bm-Aspin) makes it interesting to study because of the fact that the filarial parasite never encounters the host digestive system. Here, the aspartic protease inhibition kinetics of Bm-Aspin and its NMR structural characteristics have been investigated. The overall aim of this study is to explain the inhibition and binding properties of Bm-Aspin from its structural point of view. UV-spectroscopy and multi-dimensional NMR are the experiments that have been performed to understand the kinetic and structural properties of Bm-Aspin respectively. The human aspartic proteases that are considered for this study are pepsin, renin, cathepsin-E and cathepsin-D. The results of this analysis performed with the specific substrate [Phe-Ala-Ala-Phe (4-NO2)-Phe-Val-Leu (4-pyridylmethyl) ester] against aspartic proteases suggest that Bm-Aspin inhibits the activities of all four human aspartic proteases. The kinetics studies indicate that Bm-Aspin follows a competitive mode of inhibition for pepsin and cathepsin-E, non-competitive for renin and mixed mode for cathepsin-D. The triple resonance NMR experiments on Bm-Aspin suggested the feasibility of carrying out NMR studies to obtain its solution structure. The NMR titration studies on the interactions of Bm-Aspin with the proteases indicate that it undergoes fast-exchange phenomena among themselves. In addition to this, the chemical shift perturbations for some of the residues of Bm-Aspin observed from (15)N-HSQC spectra upon the addition of saturated amounts of aspartic proteases suggest the binding between Bm-Aspin and human aspartic proteases. They also provide information on the variations in the intensities and mode of binding between the proteases duly corroborating with the results from the protease inhibition assay method.

Identification of thermophilic bacterial strains producing thermotolerant hydrolytic enzymes from manure compost

Ten thermophilic bacterial strains were isolated from manure compost. Phylogenetic analysis based on 16S rRNA genes and biochemical characterization allowed identification of four different species belonging to four genera: Geobacillus thermodenitrificans, Bacillus smithii, Ureibacillus suwonensis and Aneurinibacillus thermoaerophilus. PCR-RFLP profiles of the 16S-ITS-23S rRNA region allowed us to distinguish two subgroups among the G. thermodenitrificans isolates. Isolates were screened for thermotolerant hydrolytic activities (60-65°C). Thermotolerant lipolytic activities were detected for G. thermodenitrificans, A. thermoaerophilus and B. smithii. Thermotolerant protease, α-amylase and xylanase activities were also observed in the G. thermodenitrificans group. These species represent a source of potential novel thermostable enzymes for industrial applications.

Accelerated cheese ripening with heat treated cells of Lactobacillus helveticus and a commercial proteolytic enzyme

Synergic effects of proteolytic enzymes from two different microbial sources on the ripening of Swedish hard cheese were studied. When extracellular proteolytic enzymes from Bacillus subtilis (Neutrase) and/or heat treated cells of Lactobacillus helveticus (now L. delbrueckii subsp. helveticus) were added to the cheese milk, cheese ripening was accelerated; Neutrase effectively hydrolysed casein to give a softer body. Addition of heat treated lactobacilli did not accelerate hydrolysis of casein, but accelerated the breakdown of peptides which increased the amount of amino acid N in the cheese and also enhanced the intensity of cheese flavour. A bitter taste which developed in cheeses with added Neutrase could be eliminated by the simultaneous addition of heat treated lactobacilli.

A micro-method for the quantitative estimation of rennets and other proteolytic enzymes

An agar diffusion slide assay using a thin layer of calcium caseinate has been developed as a micro-method for the quantitative study of calf rennet and other proteolytic enzymes. The number and width of the precipitation zones formed as a result of proteolytic activity depended upon the enzyme used, the concentration of calcium ion, pH and temperature. The assay was highly reproducible and particularly suitable for the measurement of large numbers of samples. It was considerably more sensitive than the milk clotting technique and, in general, more sensitive than other standard methods for measuring proteolytic activity.

Factors affecting the retention of rennet in cheese curd

The coagulant retained in cheese curd is a major contributor to proteolysis during ripening. The objective of this study was to quantify the effects of several milk-related factors and parameters during cheese manufacture on the retention of coagulant in cheese curd. The amount of coagulant retained in curd was determined by its activity on a synthetic heptapeptide (Pro-Thr-Glu-Phe-[NO2-Phe]-Arg-Leu) using reversed-phase HPLC. The retention of chymosin in cheese curd increased significantly when the pH of milk was reduced at rennet addition below pH 6.1, the pH at whey drainage below pH 5.7, or the average casein micelle size in milk and when the ionic strength of milk was increased. The casein content of milk and the quantity of chymosin added to milk had no significant effect on the retention of chymosin in curd; the quantity of coagulant bound per gram of casein remained unchanged.

A modification for increasing the sensitivity of the casein-agar plate assay: a simple semiquantitative assay for thermophilic and mesophilic proteases

A casein-agar plate assay was used for the quantitative determination of both mesophilic and thermophilic proteases. Because many proteases are thermostable, assay at higher temperatures is possible. The sensitivity of the plate assay increased with temperature, the optimum assay temperature depending on the thermostability of the enzyme (e.g. Thermus protease, 75 degrees C; thermolysin, 65 degrees C; trypsin, 65 degrees C; alpha-chymotrypsin, 45 degrees C). A positive correlation was observed between incubation temperature and the density of the para-casein precipitate, increasing the accuracy of diameter measurement. Using this modified method, thermostable proteases could be assayed at levels well below the limits of detection of other methods (e.g. 40 pg of thermolysin and 300 pg of trypsin detectable at 65 degrees C, a 16-fold increase in the sensitivity for trypsin compared with a conventional plate assay (Fossum, K. (1970) Acta Pathol. Microbiol. Scand. Sect. B 78, 350-361)). The sensitivity of the plate assay could be further increased by the inclusion of some detergents and chaotropic agents in the gel.

The water agar test: a new test to measure the bacteriological quality of cream

A new test, the water agar test, is described that gives a qualitative index of the presence of bacteria that indicate contamination of the cream, poor storage conditions or both of these factors. The method is simple and requires little equipment. The bacteria grow in a film of diluted cream adsorbed on the surface of a non-nutrient base. After incubation at 30 +/- 0-5 degrees C. for 18-20 hr., a proteolytic and mucoid colony count is obtained which has the same percentage coefficient of variance as a standard plate count. An examination of the effect of storage at different temperatures on the types of bacteria present in cream showed that of all the tests done initially, only the water agar test could predict subsequent bacterial growth with any consistency. The multiplication of presumptive coliform organisms occurred even at 3-5 degrees C. Irrespective of the colony count, the methylene blue reduction time was not shorter than 7 1/2 hr. unless the bacteria were in the logarithmic phase of growth when sampled. A survey was made of the bacterial flora of 188 retail samples of double cream of 15 different brands. The age of the samples varied from freshly separated cream to cream that had been kept in the shop for a day longer than that recommended for sale. The water agar test was compared with the colony count, the presumptive coliform test, a confirmatory coliform count in violet red-bile agar, a lipolytic colony count, a staphylococcal count and the methylene blue reduction test.