H. Yamini Shrivastava

Copper(II) complex of a tridentate ligand: an artificial metalloprotease for bovine serum albumin

A copper(II) complex of 2, 6-bis(benzimidazo-2-yl) pyridine was synthesized and its binding properties with bovine serum albumin (BSA) has been evaluated. The binding plot obtained from the absorption titration data gives a binding constant of 2.4 (+/-0.3) x10(3) M(-1). It was found that the charge transfer band of the metal complex was perturbed in the presence of BSA. The gel electrophoresis pattern of BSA incubated with copper(II) complex shows the metalloproteolytic activity of the metal complex. In the presence of oxygen, protein undergoes site-specific cleavage by binding to the histidine residues of domain III, with the resultant formation of four fragments of molecular weight 49, 45, 22 and 17 kDa. This indicates the presence of two specific binding sites in the protein molecule. In the absence of molecular oxygen, the metal complex was found unable to cleave the protein. The circular dichroism (CD) spectrum of the isolated fragments shows nearly 38% and 32% of alpha helical content in 49 and 45 kDa fragments, respectively, which shows that the cleavage leads to no changes in the secondary structure of the protein fragments.

Structural modification and aggregation of mucin by chromium(III) complexes.

Abstract Metal ions binding to proteins regulate the functions of proteins and may also lead to structural changes. In this communication we demonstrate the interaction and subsequent conformational changes induced in pig gastric mucin (PGM) upon binding to certain chromium(III) complexes like, [Cr(salen)(H2O)2](ClO4) (1), [Cr(en)3]Cl3 (2) and [Cr(EDTA)(H2O)]Na (3) which vary in charge and ionic character. Complexes 1 and 3 have been shown to interact coordinately with PGM whereas complex 2 binds through electrostatic interaction and hydrogen bonding. Steady state fluorescence experiment reveals that at lower concentration of complex 2 there is partial quenching of the tyrosine emission, whereas at higher concentration of the complex the emission intensity is enhanced. On the other hand with complexes 1 and 3 a decrease in fluorescence intensity was observed. PGM viscosity was found to decrease in the presence of complex 1 and 3 due to the formation of flexible fibres through coordinate interaction. Complex 2 was found to facilitate metal induced intertangling of PGM fibres which tends to stabilize the interaction and leads to sol-gel transition with subsequent increase in viscosity. A significant change in CD spectrum of PGM was observed in the presence of complex 2 where random coil spectrum became typical of a α-helical structure with 80% alpha helix content. In the case of complexes 1 and 3 only minor changes in the amplitude of the spectrum were observed. Histochemical analysis supports the contention that complex 2 favors the oligomerisation of PGM and leads to the formation of aggregated mass of macromolecules.

Insight into structural transition, aggregation and folding of glycoprotein in the presence of chromium(III) complexes by spectroscopic, microscopic and kinetic studies

An octahedral complex of chromium, tris(ethylenediamine)chromium(III) chloride which is known to exhibit ionic interaction with the protein has been found to bring about structural transition in the protein conformation. The binding of tris(ethylenediamine)chromium(III) chloride to mucin was found to bring about transition of native random coil structure to α helix with the resultant formation of aggregates as evidenced by circular dichroic and infrared spectroscopy and atomic force microscopy. This conformational change was accompanied by protein folding as depicted by change in the fluorescence intensity of the protein fluorophore in the presence of tris(ethylenediamine)chromium(III) chloride.

Molecular organization and aggregation of mucin at air-water interface in the presence of chromium(III) complexes

Abstract The interfacial organization of mucin (glycoprotein) in the presence of chromium(III) complexes has been assessed from the surface pressure–molecular area ( π –A) isotherms in Langmuir films at air–water interface and the surface energy of their LB films through contact angle measurements. At pH 7.0, the electrostatic interaction of [Cr(en) 3 ]Cl 3 with mucin was found to bring about changes in the average surface area from 3.26 to 1.47 nm 2 ; suggesting the possible formation of large aggregates of mucin. Adsorption experiments using surface potential measurements reveal that [Cr(en) 3 ]Cl 3 binds at a much faster rate to the available binding sites in mucin when compared to [Cr(salen)(H 2 O) 2 ](ClO 4 ) which binds coordinatively to mucin.

Aggregation of mucin by chromium(III) complexes as revealed by electrokinetic and rheological studies: influence on the tryptic and O-glycanase digestion of mucin.

Abstract In the present study, the impact of chromium(III) complexes ([Cr(salen)(H2O)2]+ (1), [Cr(en) 3]3+ (2) and [Cr(EDTA)(H2O)]− (3)) on the biophysical properties of mucin like specific viscosity, zeta potential and particle size has been investigated. It is evident from the present investigation that the nature of the coordinated ligand has a major role to play in bringing about the changes in the physical characteristics of the glycoprotein. It was observed that (1) and (3) because of their coordinate mode of binding lead to decrease in the specific viscosity of mucin, whereas (2) on the other hand was found to bring about drastic increase in the mucin viscosity due to sol-gel transition in the mucin conformation. Complex (2) was found to gradually lower the zeta potential value of mucin (particle size = 51.5 nm) from −24.8 ±1.31 mV to −0.58 ± 0.30 mV, which reveals aggregation (particle size = 216 nm) and subsequent sedimentation of mucin with an increase in the average diameter of mucin particles. The binding of (2) to mucin was found to impart resistance to mucin against both tryptic and O-glycanase digestion, suggesting that, the aggregation of mucin causes conformational as well as configurational changes in the glycoprotein; thus perturbing the location of carbohydrate domains.