Biophysical studies on the interaction of natural alkaloids and analogs with heme proteins
IR@IICB: CSIR-Indian Institute of Chemical Biology, Kolkata
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| Title |
Biophysical studies on the interaction of natural alkaloids and analogs with heme proteins
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| Creator |
Hazra, Soumitra
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| Subject |
Chemistry
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| Description |
Alkaloids represent an extensive group of secondary metabolites of plants with wide distribution in nature, diverse structures and with remarkable biological activities. Alkaloids and similar compounds with fused aromatic rings have the potential to form molecular
complexes with nucleic acids and proteins, and these are thought to be the cause of their therapeutic activity. Isoquinoline alkaloids such as berberine, palmatine, coralyne and sanguinarine (iminium and alkanolamine forms) have been established to have diverse biological and pharmacological activities and prospects to be developed as potential drugs for various therapies. Studies on the binding of drugs to proteins are of great importance in biological, biomedical and pharmaceutical sciences. Binding to proteins, particularly the transport proteins, is an
important element in determining the absorption, transport, distribution, cellular uptake, and activity of drugs in the circulatory systems. Binding parameters are indeed fundamental factors in determining the overall pharmacological activity of a drug. The concentration of
hemoglobin (Hb) in the blood stream (330 mg/mL) is much higher than those of the serum albumins (40 mg/mL). Even though Hb is not in the plasma, but will be available under
certain diseased conditions, it is important to study the interaction of potential drug candidates with Hb. An analysis of the complexation to Hb will provide informationon the pharmacological action and bioavailability of the drugs in the body. Furthermore, an
understanding of the details of the pharmaceutical interactions with heme proteins, hemoglobin ad myoglobin can also suggest new information on drug therapy and design as the second step in rational drug design.This thesis attempts to reveal the biophysical aspects of interaction of these protoberberine and benzophenanthridine alkaloids (isoquinolines) with heme proteins, using spectrophotometric, spectrofluorimetric and spectropolarimetric studies, and the thermodynamics of the interaction using isothermal titration calorimetry and differential scanning calorimetry tools. This thesis also aims to advance the knowledge by determining
the mode of binding to the proteins, correlating structural and energetic aspects on the interaction of these molecules with heme proteins for designing new natural product based
therapeutic molecules. Spectrophotometric studies showed that the interaction of these isoquinoline alkaloids with
heme proteins resulted in a hypochromic effect in the protein spectra and spectrofluorimetric studies revealed a significant quenching of the fluorescence of both proteins and the alkaloids. Föster resonance energy transfer (FRET) study showed that energy transfer from protein tryptophan residues (β-Trp36 of Hb) to the all alkaloids occurred with great possibility with the distances between the alkaloids and Trp of 2-8 nm in all cases. Circular dichroism, three dimensional fluorescence and synchronous fluorescence data suggested that binding of these alkaloids changed the conformation of the proteins, causing a reduction in
its -helical content. All the alkaloids were found to bind both heme proteins with moderate to high affinity with a binding constants ranging from 104-106 M-1. Overall the study suggested a higher binding affinity of sanguinarine iminium form to hemoglobin and coralyne to myoglobin.
Calorimetric studies were used to characterize the thermodynamics of the complexation.Enthalpy and entropy contributions at different temperatures were determined for all complexation. A unique phenomenon of enthalpy-entropy compensation was seen in some systems. The heat capacity changes derived from the temperature dependence of enthalpy
gave negative values in each system suggesting that the binding is specific and accompanied by the burial of non-polar surface area of proteins and also confirming the involvement of different interacting forces in the complexation. The results of structural and thermodynamic studies on the binding of these alkaloids to heme proteins provide important data in assessing the toxicity and risk factors in using these alkaloids as drugs and their distribution at the physiological sites. Furthermore, these results may help in the screening and design of appropriate isoquinoline based scaffolds that could be useful for developing as therapeutic agents.
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| Date |
2016
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| Type |
Thesis
NonPeerReviewed |
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| Format |
application/pdf
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| Identifier |
http://www.eprints.iicb.res.in/2504/1/SOUMITRA_HAZRA_THESIS.pdf
Hazra, Soumitra (2016) Biophysical studies on the interaction of natural alkaloids and analogs with heme proteins. PhD thesis, J U. |
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| Relation |
http://www.eprints.iicb.res.in/2504/
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