M. Islam Khan

Extracellular biosynthesis of silver nanoparticles using the fungus Fusarium oxysporum

The development of reliable, eco-friendly processes for the synthesis of nanomaterials is an important aspect of nanotechnology today. One approach that shows immense potential is based on the biosynthesis of nanoparticles using biological micro-organisms such as bacteria. In this laboratory, we have concentrated on the use of fungi in the intracellular production of metal nanoparticles. As part of our investigation, we have observed that aqueous silver ions when exposed to the fungus Fusarium oxysporum are reduced in solution, thereby leading to the formation of an extremely stable silver hydrosol. The silver nanoparticles are in the range of 5-15 nm in dimensions and are stabilized in solution by proteins secreted by the fungus. It is believed that the reduction of the metal ions occurs by an enzymatic process, thus creating the possibility of developing a rational, fungal-based method for the synthesis of nanomaterials over a range of chemical compositions, which is currently not possible by other microbe-based methods.

Extracellular Synthesis of Gold Nanoparticles by the Fungus Fusarium oxysporum

A green chemistry approach to nanoparticle synthesis is the exciting possibility opened up by the fungus Fusarium oxysporum. The fungus, when exposed to aqueous AuCl 4 − ions, reduces the metal ions; this leads to the extracellular formation of gold nanoparticles.

Intracellular synthesis of gold nanoparticles by a novel alkalotolerant actinomycete, Rhodococcus species

The development of reliable, eco-friendly processes for the synthesis of nanoscale materials is an important aspect of nanotechnology. In this paper, we report on the use of an alkalotolerant actinomycete (Rhodococcus sp.) in the intracellular synthesis of gold nanoparticles of the dimension 5–15 nm. Electron microscopy analysis of thin sections of the gold actinomycete cells indicated that gold particles with good monodispersity were formed on the cell wall as well as on the cytospasmic membrane. The particles are more concentrated on the cytoplasmic membrane than on the cell wall, possibly due to reduction of the metal ions by enzymes present in the cell wall and on the cytoplasmic membrane. The metal ions were not toxic to the cells and the cells continued to multiply after biosynthesis of the gold nanoparticles.

Protein A: nature's universal anti-antibody

Staphylococcal protein A specifically interacts with immunogobulins. This fact is being used in various disciplines of biology and some of the unique properties of protein A and their applications are summarized in this review.

Sulfite reductase‐mediated synthesis of gold nanoparticles capped with phytochelatin

An enzymatic synthesis route to peptide‐capped gold nanoparticles has been developed. Gold nanoparticles were synthesized using α‐NADPH‐dependent sulfite reductase and phytochelatin in vitro. The gold ions were reduced in the presence of the enzyme sulfite reductase, leading to the formation of a stable gold hydrosol of dimensions 7–20 nm and were stabilized by the capping peptide. The nanoparticles were characterized by X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy and UV–visible optical absorption. These studies will help in designing a rational enzymatic strategy for the synthesis of nanomaterials of different chemical compositions, shapes and sizes as well as their separation.

Studies on recombinant single chain Jacalin lectin reveal reduced affinity for saccharides despite normal folding like native Jacalin

Sugar binding studies, inactivation, unfolding, and refolding of native Jacalin (nJacalin) from Artocarpus integrifolia and recombinant single‐chain Jacalin (rJacalin) expressed in Escherichia coli were studied by intrinsic fluorescence and thermal and chemical denaturation approaches. Interestingly, rJacalin does not undergo any proteolytic processing in an E. coli environment. It has 100fold less affinity for methyl‐α‐galactose (Ka: 2.48 × 102) in comparison to nJacalin (Ka: 1.58 × 104), and it also binds Thomsen‐Friedenreich (TF) disaccharide (Galβ1–3GalNAc) with less affinity. Overall sugar binding characteristics of rJacalin are qualitatively similar to that of nJacalin (Gal

Crystallization and preliminary X-ray studies of the anti-T lectin from peanut (Arachis hypogaea)

The anti-T lectin from peanut (Arachis hypogaea) crystallizes in the orthorhombic space group P21212 with one tetrameric molecule (Mr 110,000) in the asymmetric unit in a cell of dimensions a = 129.3 A, B = 126.9 A and C = 76.9 A. The crystals are suitable for high resolution work.

Interaction of Fusarium solani lectin with monosaccharides and oligosaccharides: a fluorometric study.

The intrinsic fluorescence intensity of Fusarium solani lectin was quenched upon binding to mono‐ and oligosaccharides without any change in the emission maximum and it was used to determine association constants for several sugars and glycans. The lectin interacted very poorly with monosaccharides but well with disaccharides (T‐antigen and LacNAc) with a distinction between β1→4 and β1→3 linkages. Among the monosaccharides, the interaction was observed only with Gal/GalNAc derivatives and not with Glc/Man derivatives. Thermodynamic studies revealed that the binding of the lectin with all the saccharides is enthalpically driven and exothermic in nature. Asialo‐triantennary N‐glycan and asialo‐biantennary N‐glycan showed higher affinity than monovalent LacNAc with significant increase in binding enthalpy, pointing towards the importance of multivalency in the lectin–ligand interactions. Time‐resolved fluorescence measurement indicated the lectin has two lifetimes for tryptophan and the shorter lifetime is affected on ligand binding.

Chemical, thermal and pH-induced equilibrium unfolding studies of Fusarium solani lectin.

The effect of urea, guanidine thiocyanate, temperature and pH was studied on the conformational stability of Fusarium solani lectin. Equilibrium unfolding with chemical denaturants showed that the lectin was least stable at pH 12 and maximally stable at pH 8.0 near its pI (8.7). Guanidine thiocyanate (the concentration of denaturant at which the protein is half folded, D1/2 = 0.49 M at pH 12) was found to be an eight times stronger denaturant than urea (D1/2 = 3.88 M at pH 12). The unfolding curves obtained with fluorescence and CD measurements showed good agreement indicating a monophasic nature of unfolding and excluded the possibility of formation of any stable intermediate. The effect of pH on the lectin was found to be unusual as at acidic pH, the lectin showed a flexible tertiary structure with pronounced secondary structure, and retained its hemagglutinating activity. On the other hand, the lectin did not show any loss of conformation or activity upto 70°C for 15 min. Moreover, thermal denaturation did not result in the aggregation or precipitation of the protein even at high temperatures. Thermal denaturation was also carried out in the presence of a low concentration of guanidine thiocyanate. Change in the enthalpy of transition (ΔHm) varied linearly with transition temperature (Tm), which indicated that the heat capacity (ΔCp = 3.95 kJ · mol‐1 · K‐1) of the lectin remained constant during the unfolding. IUBMB Life, 59: 34‐43, 2007

Taxol and 10-deacetylbaccatinIII induce distinct changes in the dynamics of caveolae

Taxol treatment of HeLa cells resulted in a transient recruitment of Caveolin‐1 to the cell surface followed by internalization. Interestingly, 20 min after 10‐deacetylbaccatinIII (10‐DAB) treatment, the caveolae displayed faster ‘kiss and run’ dynamics while BaccatinIII (BacIII) did not induce any change. Sustained phosphorylation of Caveolin‐1 is observed upon treatment and between Taxol and 10‐DAB, the former shows phosphorylated Raf‐1, ERK1/2 and hyperphosphorylated Bcl‐2 while the later showed much less magnitude of the same. BacIII treatment did not induce phosphorylation of Raf‐1 or Bcl‐2. It is possible that Taxol might act on multiple targets and the side chain may be crucial.