Biomedical subjects
Publications and source records attributed to M N Gupta.
Lysozyme, a well-characterized protein which is known to be devoid of any carbohydrate residues, was found to interact with Con A. This interaction could be inhibited by high salt concentration or ethylene glycol or specific sugars. These results indicate that the protein part of glycoproteins may play an important role in lectin-glycoprotein interactions.
Reaction of proteins with bisimidoesters is one of the popular crosslinking techniques. The extent of the reaction cannot be followed directly using the commonly used free amino group-determining reagents ninhydrin and 2,4,6-trinitrobenzene sulfonic acid since they react with bisimidoesters. However, we found that the extent of amidination of protein could be followed colorimetrically by using 1-fluoro-2,4-dinitrobenzene.
When concanavalin A (Con A) is reacted with a low concentration of glutaraldehyde, the product formed strongly binds to DEAE-cellulose. Thus, the resultant material can be used as an affinity medium for those glycoproteins which interact with Con A. This affinity medium is easy to prepare, has a capacity comparable to that of similar commercially available affinity media, and is stable for up to at least 6 months.
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The accessibility of methionines in RNAase A to reaction with OBQ has been studied at highly acidic pH. The differences between the rate constants of reactions of the methionine and methionines of RNAase A with OBQ is a reflection on the limited accessibility of methionines in the protein conformation. Nevertheless, at sufficiently high OBQ concentration, all the four methionines of the enzyme can be modified. At lower concentration of OBQ, a derivative may be prepared in which a specific methionine is modified. The introduced chromophore ionizes at around pH 3 in this derivative. The derivative has partial activity towards RNA which is enhanced on addition of S-protein.
OBQ reacts specifically with methionine residues of RNAase A at highly acidic pH. At pH 3, whereas RNAase A does not react, RNAase S, S-protein and S-peptide all react with OBQ. RNAase A derivatives in which some of the methionines have been initially modified at pH 1, further react with OBQ at pH 3. Thus, reaction with OBQ can be used to monitor structural transitions and conformational differences involving methionines in proteins.
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Affinity precipitation is being studied as a technique to be introduced at an early stage of downstream processing for the selective isolation of proteins. The technique utilizes a heterobifunctional ligand, which, in addition to having affinity for the target protein(s), possesses another function for controlling precipitation. The latter component is comprised of a polymer which can be made reversibly soluble and insoluble by altering a specific parameter such as pH or temperature. Different polymers of natural and synthetic origin have been used for this purpose. The soluble form of the ligand is used for the affinity binding step and precipitation is induced for obtaining separation of the affinity complex. Some of the polymers used in this laboratory include chitosan, alginate, Eudragit S-100 (copolymer of methacrylic acid and methyl methacrylate) and polyethyleneimine. Chitosan and alginate served as natural ligands for wheat germ agglutinin and pectinase, respectively. The aromatic dye Cibacron Blue 3GA coupled to Eudragit S 100 and polyethyleneimine way used for the affinity precipitation of some model enzymes such as lactate dehydrogenase and alcohol dehydrogenase. As prior removal of cell debris, etc., is essential for affinity precipitation, the possibility of integration of the technique with extraction in aqueous two-phase systems was also demonstrated.
It was found that alginate binds to glucoamylase, presumably through the recognition of starch binding domain of the latter. The present work exploits this for purification of glucoamylases from commercial preparation of Aspergillus niger and crude culture filtrate of Bacillus amyloliquefaciens by affinity precipitation technique in a single-step protocol. Glucoamylase is selectively precipitated using alginate as macroaffinity ligand and later eluted with 1.0 M maltose. In the case of A. niger, 81% activity is recovered with 28-fold purification. The purified glucoamylase gave a single band on SDS-PAGE corresponding to 78 kDa molecular weight. The developed affinity precipitation process also works efficiently for purification of Bacillus amyloliquefaciens glucoamylase from its crude culture filtrate, giving 78% recovery with 38-fold purification. The purified preparation showed a major band corresponding to 62 kDa and a faint band about 50 kDa on SDS-PAGE. The latter corresponds to the molecular weight for alpha-amylase of Bacillus amyloliquefaciens.
beta-D-Galactosidase from E. Coli was crosslinked using glutaraldehyde and two bisimidoesters. With glutaraldehyde and dimethyl adipimidate (DMA), it is possible to obtain preparations having higher activity than the native enzyme. Glutaraldehyde and DMA gave preparations showing enhanced thermal stability. The preparation crosslinked with DMA, when used for continuous hydrolysis of lactose in milk, was found to be significantly better than the native enzyme.
A heteroenzyme conjugate retaining activities of two component enzymes from trypsin and chymotrypsin was prepared using N-succinimidyl pyridyl dithiopropionate as crosslinking reagent. The conjugate bound to both trypsin and chymotrypsin affinity columns. Trypsin and chymotrypsin were linked in the ratio of 1:1 on mol basis. The conjugate, when treated with dimethyladipimidate, showed decreased autolysis of its trypsin component.
We have identified a chitinase with antifungal activity in the bulbs of the plant Urginea indica(Indian squill) and purified it about 26-fold. The purified preparation contained a Mr 29 kDa protein that was an active growth inhibitor of the fungal pathogens Fusarium oxysporum and Rhizoctonia solani in an in vitro assay. Amino acid sequence analysis of the Mr 29 kDa protein revealed it to be highly homologous to the family 19 glycoside hydrolases, which are known to possess chitinase activity. The U. indica chitinase lacked a cysteine-rich N-terminal domain (characteristic of class I chitinases) and contained a conserved motif indicative of the signature 1 of family 19 glycoside hydrolases. It shared a approximately 70% sequence identity with the 26 kDa endochitinase of Hordeum vulgare, a typical class II chitinase of family 19. The five cysteines in the partial sequence of the Mr 29 kDa chitinase were found to be identical in location to five of the seven cysteines present in the catalytic domain of the H. vulgare enzyme. The molecular weight, the lack of an N-terminal cysteine-rich sequence, and the striking identity to the H. vulgare endochitinase suggest that the Mr 29 kDa U. indica protein is a putative class II chitinase. The antifungal activity is presumably mediated through the chitinolytic activity of the Mr 29 kDa protein.
For the first time, it is demonstrated that exposure of an enzyme to anhydrous organic solvents at optimized high temperature enhances its catalytic power through local changes at the binding region. Six enzymes, namely, proteinase K, wheat germ acid phosphatase, alpha-amylase, beta-glucosidase, chymotrypsin and trypsin were exposed to acetonitrile at 70 degrees C for three hr. The activities of these enzymes were found to be considerably enhanced. In order to understand the basis of this change in the activity of these enzymes, proteinase K was analyzed in detail using X-ray diffraction method. The overall structure of the enzyme was found to be similar to the native structure in aqueous environment. The hydrogen bonding system of the catalytic triad remained intact after the treatment. However, the water structure in the substrate binding site underwent some rearrangement as some of the water molecules were either displaced or completely absent. The most striking observation concerning the water structure was the complete deletion of the water molecule which occupied the position at the so-called oxyanion hole in the active site of the native enzyme. Three acetonitrile molecules were found in the present structure. All the acetonitrile molecules were located in the recognition site. Interlinked through water molecules, the sites occupied by acetonitrile molecules were independent of water molecules. The acetonitrile molecules are involved in extensive interactions with the protein atoms. The methyl group of one of the acetonitrile molecules (CCN1) interacts simultaneously with the hydrophobic side chains of Leu 96, Ile 107 and Leu 133. The development of such a hydrophobic environment at the recognition site introduced a striking conformation change in Ile 107 by rotating its side chain about C alpha-C beta bond by 180 degrees to bring about the delta-methyl group within the range of attractive van der Waals interactions with the methyl group of CCN1. A similar change had earlier been observed in proteinase K when it was complexed to a substrate analogue, lactoferrin fragment.