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H Zakaria

Publications and source records attributed to H Zakaria.

4 recordsLinked to original sources
PubMed2005

Quantification and characterisation of Trichoderma spp. from different ecosystems.

Basal stem rot of oil palm caused by Ganoderma boninense is of major economic importance. Observations of the low incidence of disease due to Ganoderma species in natural stands, suggest that the disease is kept under control by some biological means. Trichoderma spp. are saprophytic fungi with high antagonistic activities against soil-borne pathogens. However, their abundance and distribution are soil and crop specific. Trichoderma species have been found to be concentrated in the A1 (0-30 cm) and Be soil horizons (30-60 cm), although the abundance of Trichoderma was not significantly different between the oil palm and non-oil palm ecosystems. Characterisation of Trichoderma isolates based on cultural, morphological and DNA polymorphism showed that T. harzianum, T. virens, T. koningii and T. longibrachiatum made up 72, 14, 10 and 4% of the total Trichoderma isolates isolated. As Trichoderma species are present in the oil palm ecosystem, but at lower numbers and in locations different from those desired, soil augmentation with antagonistic Trichoderma spp. can be developed as a strategy towards integrated management of basal stem rot of oil palm.

Arecaceae↗
PubMed1996

Computer-aided modeling of structure stabilizing disulfide bonds in recombinant human interferon-gamma.

We present a general search algorithm for possible insertion sites of disulfide bonds in proteins based on the coordinates of the solved X-ray or NMR structure, allowing the insertion of disulfide bonds with a minimum of conformational tension and backbone rearrangements. The FORTRAN 77 program "Ssuitable' was written for this purpose. This methodological approach was applied to recombinant human interferon-gamma (rhu-IFN-gamma), a cytokine of great pharmaceutical interest with a wide variety of biological activities including antiviral, antiproliferative and immunomodulatory effects. A model based on the C alpha-coordinates obtained from the Brookhaven data base was built. Four different insertion sites were selected in the model, connecting the two subunits of the homodimer. The thermodynamic stability of rhu-IFN-gamma is low, limiting its clinical application. We expect that the insertion of additional new disulfide bonds will enhance the thermodynamic stability as well as protect the protein against proteolytic degradation.

Amino Acid Sequence↗
PubMed1996

Engineered disulfide bonds in recombinant human interferon-gamma: the impact of the N-terminal helix A and the AB-loop on protein stability.

Insertion sites for cysteines with optimal stereochemistry for the formation of unstrained disulfide bridges were identified in recombinant human interferon-gamma (rhu-IFN-gamma) by computer modelling. We have engineered two different disulfide cross-linked mutants, containing a pair of symmetry-related disulfide bonds, which stabilize the N-termini of both monomers of the homodimeric protein. Mutations E7C and S69C allow the formation of an intramonomer disulfide bond between helices A and D. In contrast, the A17C and H111C mutations lead to a covalent cross-link between both monomers. The AB-loop is linked to helix F. The fluorescence properties of native and disulfide cross-linked proteins were studied as a function of guanidine hydrochloride concentration. Melting temperatures (Tm) were calculated from the decrease in CD ellipticity at 220 nm. The induction of the antiviral effect was measured using A549 fibroblast cells infected with encephalomyocarditis virus. The ability to induce the expression of the HLA-DR antigen in Colo 205 cells was determined by fluorescence-activated cell scanning analysis. The stability of both mutants was strongly enhanced against temperature- and cosolvent-induced unfolding. The delta Tm of mutant IFN-gamma E7C/S69C was 15 degrees C. All measured biological activities of this mutant were equal to wild type. In the case of the other mutant IFN-gamma A17C/H111C, the delta Tm value was 25 degrees C. This mutation abolishes nearly the entire biological activity (< 1%) with no detectable changes of secondary structure in the CD spectrum. Our results illustrate the importance of the N-terminal helix A and the AB-loop for the unfolding pathway and thermodynamic stability of rhu-IFN-gamma.

Circular Dichroism↗