-
[show abstract]
[hide abstract]
ABSTRACT: Recent research has shown that, like porphyrins, phycocyanin (PC) too can produce singlet oxygen upon excitation with the appropriate radiation and hence could be useful in photodynamic therapy (PDT) for cancer. Unlike porphyrins, PC has the advantage of being a non-toxic, non-carcinogenic, soluble protein. However, the challenge would be to target the fluorescent phycobiliprotein to malignant cells. We report here that the tumor-specific lectin, jacalin, binds PC specifically in a carbohydrate-independent manner and with affinities better than that for porphyrins. Hence the lectin could prove to be a useful carrier for targeted delivery of PC. The interaction involves both ionic and hydrophobic interactions and more than one contact site.
Journal of photochemistry and photobiology. B, Biology 09/2009; 97(2):87-93. · 1.87 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The neurokinin-2 receptor is a member of the rhodopsin family of G-protein coupled receptors, which represents one of the most relevant target families in small-molecule drug design. NK-2 receptors have been implicated in playing a pathophysiological role in asthma. Activation of the NK-2 receptor by its endogenous peptide agonist, tachykinins, is associated with diverse biological responses like bronchoconstriction, vasodepression, and regulation of endocrine functions. Agonist binding to the receptor is a crucial event in initiating signaling, and therefore characterization of the structural features of the agonists can reveal the molecular basis of receptor activation and help in rational design of novel therapeutics. In this study a molecular model for the interaction of the primary ligand NKA with its G-protein coupled receptor neurokinin-2 receptor has been developed. A three-dimensional model for the NK-2 receptor has been generated by homology modeling using rhodopsin as a template. A knowledge based docking of the NMR derived bioactive conformation of NKA to the receptor has been performed utilizing the ligand binding data obtained from the photoaffinity labeling and site-directed mutagenesis studies. The molecular model for the NKA/NK-2 receptor complex thus obtained sheds light on the topographical features of the binding pocket of the receptor and provides atomic insight into the biochemical data currently available for the receptor. The results of the receptor modeling studies have been used to discuss the molecular determinants for NK-2 receptor selectivity.
Journal of Chemical Information and Modeling 07/2009; 49(7):1734-40. · 4.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Phyllomedusin, an amphibian tachykinin decapeptide, has been shown to be selective for Neurokinin 1 receptor. Because the micelle-associated structure may be relevant to the Phyllomedusin-receptor interaction, the three-dimensional structure of the Phyllomedusin in aqueous and micellar environments has been studied by two-dimensional proton nuclear magnetic resonance (2D (1)H NMR spectroscopy) and distance geometry calculations. Sequence specific resonance assignments of protons have been made from correlation spectroscopy (TOCSY, DQF-COSY) and NOESY spectroscopy. The interproton distance constraints and dihedral angle constraints have been utilized to generate a family of structures using DYANA. The CD and NMR results show that, while in water Phyllomedusin prefers to be in an extended chain conformation, whereas in the presence of dodecylphosphocholine micelles, a membrane model system, a partial helical conformation is induced. Analysis of NMR data indicates that the global fold of Phyllomedusin can be explained in terms of equilibrium between 3(10)-helix and alpha-helix from residue 4 to 10. An extended highly flexible N-terminus displays some degree of order and a possible turn structure. A comparison between the conformational features of Phyllomedusin and different Neurokinin 1 receptor agonist indicates several common features in the distribution of hydrophobic and hydrophilic residues. The conformational similarities suggest that the molecules interact with receptor in an analogous manner.
Journal of Structural Biology 06/2009; 167(2):176-84. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Scyliorhinin II, a cyclic Tachykinin peptide, is a potent NK3 receptor agonist. The pharmacology of NK3 receptor is least characterized out of the three tachykinin receptor subtypes cloned and characterized for Tachykinins. To understand the structural basis of peptide-receptor interaction, the three-dimensional structure of the Scyliorhinin II in aqueous and micellar environments has been studied by two-dimensional proton nuclear magnetic resonance (2D 1H-NMR spectroscopy) and distance geometry calculations. Proton NMR assignments have been carried out with the aid of correlation spectroscopy (gradient-COSY and TOCSY) and nuclear Overhauser effect spectroscopy (NOESY and ROESY) experiments. The inter proton distances and dihedral angle constraints obtained from the NMR data have been used in torsion angle dynamics algorithm for NMR applications (DYANA) to generate a family of structures, which have been refined using restrained energy minimization and dynamics. The results show that in an aqueous environment, Scyliorhinin II lacks a definite secondary structure. The structure is well-defined in presence of dodecyl phosphocholine micelles. The global fold of Scyliorhinin II bound to DPC micelles consists of a well-defined helix in the C-terminal region from residue 12-18 and a series of turns towards N-terminus. The structure is further stabilized by disulfide bond between Cys7 and Cys13. The conformational range of the peptide revealed by NMR and CD studies has been analyzed in terms of characteristic secondary features. Observed conformational features have been compared with those of Substance P, Neurokinin A and Neurokinin B, potent NK1, NK2, and NK3 agonists, respectively.
Journal of biomolecular structure & dynamics 03/2008; 25(4):395-405. · 4.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The proximal portion of the C-terminus of the CB(1) cannabinoid receptor is a primary determinant for G-protein activation. A 17 residue proximal C-terminal peptide (rodent CB1 401-417), the intracellular loop 4 (IL4) peptide, mimicked the receptor's G-protein activation domain. Because of the importance of the cationic amino acids to G-protein activation, the three-dimensional structure of the IL4 peptide in a negatively charged sodium dodecyl sulfate (SDS) micellar environment has been studied by two-dimensional proton nuclear magnetic resonance (2D (1)H NMR) spectroscopy and distance geometry calculations. Unambiguous proton NMR assignments were carried out with the aid of correlation spectroscopy (DQF-COSY and TOCSY) and nuclear Overhauser effect spectroscopy (NOESY and ROESY) experiments. The distance constraints were used in torsion angle dynamics algorithm for NMR applications (DYANA) to generate a family of structures which were refined using restrained energy minimization and dynamics. In water, the IL4 peptide prefers an extended conformation, whereas in SDS micelles, 3(10)-helical conformation is induced. The predominance of 3(10)-helical domain structure in SDS represents a unique difference compared with structure in alternative environments, which can significantly impact global electrostatic surface potential on the cytoplasmic surface of the CB(1) receptor and might influence the signal to the G-proteins.
Journal of Structural Biology 10/2007; 159(3):359-68. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Uperolein, a physalaemin-like endecapeptide, has been shown to be selective for Neurokinin 1 receptor. As a first step towards understanding the structure-activity relationship, we report the membrane-induced structure of Uperolein with the aid of circular dichroism and 2D (1)H NMR spectroscopy. Sequence-specific resonance assignments of protons have been made using correlation spectroscopy (TOCSY, DQF-COSY) and NOESY spectroscopy. The interproton distance constraints and dihedral angle constraints have been utilized to generate a family of structures using torsion angle molecular dynamics within program DYANA. The conformational range of the peptide revealed by NMR and CD studies has been analysed in terms of characteristic secondary features. Analysis of NMR data indicates that the global fold of Uperolein can be explained in terms of equilibrium between 3(10)-helix and alpha-helix from residues 5 to 11. An extended highly flexible N-terminus displays some degree of order and a possible turn structure. A comparison between the structures of Uperolein and Substance P, a prototype and endogenous Neurokinin 1 receptor agonist, indicates several common features in the distribution of hydrophobic and hydrophilic residues. Both the peptides show an amphiphilic character towards the middle region. The similarities suggest that the molecules interact with the receptor in an analogous manner.
Journal of Structural Biology 01/2007; 156(3):442-52. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The mammalian tachykinin (TK) peptides and their three Neurokinin (NK1, NK2 and NK3) receptors represent an effector system with wide-ranging actions on neuronal, airway smooth muscle, mucosal, endothelial, immune, inflammatory and remodeling cell function. Recent clinical and preclinical data suggests the pathophysiological role of TKs in various diseases including asthma, emesis and depression. The TK-NK receptor interactions and overlapping functions mediated by each NK receptor indicate added therapeutic benefit of using multiple NK receptor blockade. In the absence of structural data on neurokinin receptors, the membrane-induced structure of tachykinins play an important role as a first step towards understanding structure-activity relationship. A comparison of the conformational features of different NK1, NK2 and NK3 receptor agonists highlights several features which might be responsible for determining selectivity for the particular receptor subtype. An attempt has been made to correlate the observed conformational differences to the binding ability and biological activity of various NK1, NK2 and NK3 receptor agonists. The membrane bound conformations of tachykinins have been used as a starting point, leading to useful pharmacophore patterns that can be used for identifying lead structures with novel scaffolds.
American Journal of Biochemistry and Biotechnology. 01/2007;
-
[show abstract]
[hide abstract]
ABSTRACT: Neuropeptide K (NPK), an N-terminally extended form of neurokinin A (NKA), represents the most potent and longest lasting vasodepressor and cardiomodulatory tachykinin reported thus far. NPK has been shown to have high selectivity for the NK2 receptor. Because the micelle-associated structure may be relevant to the NPK-receptor interaction, the three-dimensional structure of the NPK in aqueous and micellar environments has been studied by two-dimensional proton nuclear magnetic resonance (2D (1)H NMR spectroscopy) and distance geometry calculations. Proton NMR assignments have been carried out with the aid of correlation spectroscopy (DQF-COSY and TOCSY) and nuclear Overhauser effect spectroscopy (NOESY and ROESY) experiments. The interproton distances and dihedral angle constraints obtained from the NMR data have been used in torsion angle dynamics algorithm for NMR applications (DYANA) to generate a family of structures, which have been refined using restrained energy minimization and dynamics. The results show that in an aqueous environment NPK lacks a definite secondary structure, although some turn-like elements are present in the N terminus. The structure is well-defined in the presence of dodecylphosphocholine micelles. The global fold of NPK bound to DPC micelles consists of two well-defined helices from residues 9 to 18 and residues 27 to 33 connected by a noncanonical beta turn. The N terminus of the peptide is characterized by a 3(10) helix or a series of dynamic beta turns. The conformational range of the peptide revealed by NMR and circular dichroism (CD) studies has been analyzed in terms of characteristic secondary features. The observed conformational features have been further compared to a NKA and neuropeptide gamma (NPgamma) potent endogenous agonist for the NK2 receptor.
Biochemistry 04/2006; 45(9):2994-3004. · 3.42 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The effect of different concentrations (0.1-5 microM) of neurokinin B (NKB) and Abeta (25-35) on acetylcholine esterase (AChE), Na(+)-K(+) ATPase and membrane fluidity (DPH anisotropy) were investigated in rat brain synaptosomes of 3, 9, 18 and 30 months old. An age dependent decrease was observed for all the three parameters studied. An in vitro incubation of isolated brain synaptosomes with Abeta (25-35) showed toxic effects on all the parameters studied and the peptide had concentration and age dependent effects, while NKB showed stimulating effect on the parameters and the combined NKB+Abeta (25-35) incubations showed a partial reversal effect as compared to the Abeta (25-35) alone. Thus, the results suggest a membrane mediated function for NKB and its role in neuromodulation, neuroprotection and antioxidant property against Abeta (25-35) induced toxicity in aging brain functions.
Biogerontology 03/2006; 7(1):19-33. · 3.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The brain tissue has a large oxidative capacity, but its ability to combat oxidative stress is limited. In aging brain tissue the oxidative stress increases due to decreased activity of antioxidant enzymes and increased oxidative stress leading to neurodegeneration associated with excitotoxicity. The aim of the present study was to determine the effect of neuropeptides, neurokinin B (NKB) and amyloid beta protein fragment Abeta (25-35) and neurotransmitters N-methyl D-aspartate (NMDA) and Glutamate on rat brain synaptosomes of different age groups. Aging brain functions were assessed by measuring the activities of superoxide dismutase (Mn-SOD) and monoamine oxidase (MAO) and intrasynaptosomal [Ca(2+)](i )levels in presence of neuropeptides and neurotransmitters. Increase in age decreased the SOD and MAO enzyme activities; Abeta (25-35) addition further had damaging/toxic effects on the enzymes, whereas NKB alone and in combination with amyloid lowered the toxic effects caused by Abeta (25-35) addition, which was concentration (peptide) and age dependent. Oxidative stress and excitotoxicity are major consequences associated with the age, [Ca(2+)](i )was increased with the age and the neuropeptides and neurotransmitters elicited significant modulatory effects on it. Our study elucidates an increased activity of SOD, decreased activity of MAO and restoration of [Ca(2+)](i) levels in the presence of NKB and suggests an antioxidant, neuromodulatory and neuroprotective role of tachykinin peptide NKB against the beta amyloid induced toxicity.
Biogerontology 03/2006; 7(1):1-17. · 3.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The effect of different concentrations (0.1–5 μM) of neurokinin B (NKB) and Aβ (25–35) on acetylcholine esterase (AChE), Na+–K+ ATPase and membrane fluidity (DPH anisotropy) were investigated in rat brain synaptosomes of 3, 9, 18 and 30 months old.
An age dependent decrease was observed for all the three parameters studied. An in vitro incubation of isolated brain synaptosomes with Aβ (25–35) showed toxic effects on all the parameters studied and the peptide had concentration and age dependent effects, while
NKB showed stimulating effect on the parameters and the combined NKB+Aβ (25–35) incubations showed a partial reversal effect as compared to the Aβ (25–35) alone. Thus, the results suggest a membrane mediated function for NKB and its role in neuromodulation, neuroprotection
and antioxidant property against Aβ (25–35) induced toxicity in aging brain functions.
Biogerontology 01/2006; 7(1):19-33. · 3.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Scyliorhinin I, a linear decapeptide, is the only known tachykinin that shows high affinity for both NK-1 and NK-2 binding sites and low affinity for NK-3 binding sites. As a first step to understand the structure-activity relationship, we report the membrane-induced structure of scyliorhinin I with the aid of circular dichroism and 2D-(1)H NMR spectroscopy. Sequence specific resonance assignments of protons have been made from correlation spectroscopy (TOCSY, DQF-COSY) and NOESY spectroscopy. The interproton distance constraints and dihedral angle constraints have been utilized to generate a family of structures using DYANA. The superimposition of 20 final structures has been reported with backbone pairwise root mean-square deviation of 0.38 +/- 0.19 A. The results show that scyliorhinin I exists in a random coil state in aqueous environments, whereas helical conformation is induced toward the C-terminal region of the peptide (D4-M10) in the presence of dodecyl phosphocholine micelles. Analysis of NMR data is suggestive of the presence of a 3(10)-helix that is in equilibrium with an alpha-helix in this region from residue 4 to 10. An extended highly flexible N-terminus of scyliorhinin I displays some degree of order and a possible turn structure. Observed conformational features have been compared with respect to that of substance P and neurokinin A, which are endogenous agonists of NK-1 and NK-2 receptors, respectively.
Biophysical Journal 06/2005; 88(5):3592-600. · 3.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Aging of the normal brain is accompanied by changes in its structure, function, and metabolism. There are significant gender differences in aging brain. Most of these changes increase during menopausal condition in females when the level of estradiol and progesterone are decreased. The objective of this study was to determine the effect of estradiol and progesterone (separate as well as combined) hormones in neuronal tissues from naturally menopausal rats of different age groups. Results show decreased activity of Acetylcholine esterase (AChE) whereas the level of lipid peroxidation increased with age, and after the hormone treatments both AChE activity and level of lipid peroxidation returned to control values. The deposition of lipofuscin, a pigment that accumulated intraneuronally in brain and other tissues and is considered a marker of aging, was increased with aging and the hormone treatment decreased this deposition. The present study clearly shows reduction in risk factors associated with aging in the murine model system by hormone treatments, namely estrogen and progesterone by increasing the activity of acetylcholine esterase and decreasing the levels of lipid peroxidation and lipofuscin deposition in different parts of aging brain. This study suggests that hormone replacement therapy may either reduce or delay the onset of age related diseases like Alzheimer's, Parkinson's and other neurological disorders.
Biogerontology 02/2005; 6(5):345-56. · 3.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Neuropeptide gamma (NPgamma) is a neurokinin-2 (NK-2) receptor selective agonist, which plays an important role in mediation of asthma and elicits a wide range of biological responses like bronchoconstriction, vasodepression and regulation of endocrine functions. The structure determination of this peptide agonist is important in understanding the molecular basis of peptide ligand recognition by the receptor and for rational drug design. In the present study we report the solution structure of NPgamma characterized by circular dichroism (CD) spectropolarimetry and 2D (1)H NMR spectroscopy in both aqueous and membrane mimetic solvents. Effect of calcium ions on the conformation of NPgamma was also studied using CD spectropolarimetry. Sequence-specific resonance assignments of protons have been made with the aid of correlation spectroscopy experiments and nuclear Overhauser effect spectroscopy experiments. The distance constraints obtained from the NMR data have been utilized to generate a family of structures, which have been refined using restrained energy minimization and dynamics. These data show that in water NPgamma prefers to be in an extended chain conformation whereas a helical conformation is induced in the central core and the C-terminal region of the peptide (K13-M21) in the presence of perdeuterated dodecylphosphocholine micelles, a membrane model system. A type II' beta turn from H9 to R11 precedes the helical core in the C-terminus of NPgamma. N-terminus of NPgamma also displays some degree of order and a possible turn structure. Conformation adopted by NPgamma in presence of lipid micelles represents a structural motif typical of NK-2 selective agonists and is similar to that observed for Neurokinin A in hydrophobic environment. The observed conformational features have been correlated to the binding ability and biological activity of NPgamma.
Journal of Structural Biology 01/2005; 148(3):315-25. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Neurokinin B (NKB), a decapeptide of mammalian origin exhibits a variety of biological activities such as regulatory functions in reproduction, pre-eclampsia and neuroprotection in Alzheimer's disease. In order to gain insight into structure-function relationship, three-dimensional structure of NKB has been investigated using CD spectropolarimetry and two-dimensional proton nuclear magnetic resonance (2D 1H-NMR) spectroscopy in aqueous and membrane mimetic solvents. Unambiguous NMR assignments of resonances have been made with the aid of correlation spectroscopy (DQF-COSY and TOCSY) experiments and Nuclear Overhauser Effect Spectroscopy (NOESY) experiments. Distance constraints obtained from the NMR data have been used to generate a family of structures, which have been refined using restrained energy minimization and dynamics. Our data show that a helical structure is induced in NKB, in presence of perdeuterated dodecyl phosphocholine (DPC) micelles, a membrane model system. Further, the conformation adopted by NKB in presence of DPC micelles represents a structural motif typical of neurokinin-3 selective agonists.
Journal of biomolecular structure & dynamics 11/2004; 22(2):137-48. · 4.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The effect of estradiol and progesterone therapy in serum and liver on the lipid profile of naturally menopausal albino rats of the Wistar strain of different age groups (12,18 and 24 months) have been measured and compared with the age matched groups. Three months old rats were used as young controls. The aged rats were administered subcutaneous injection of 17-beta-estradiol (0.1 microg/g body weight), progesterone (2.5 microg/g body weight) and similar concentrations of both in combined treatment for 1 month and the level of triglycerides (TG), total lipids (TL), total cholesterol (TC), high density lipoprotein (HDL), low density lipoprotein (LDL) and very low density lipoprotein (VLDL) were measured in serum and liver of 3, 12, 18 and 24 months old control as well as treated groups. The results show that TG, HDL, VLDL levels were increased significantly by 71%, 155%, 54%, respectively in liver of 24 months old rats by combination treatment when compared with age matched control animals. The levels of TL, TC and LDL were decreased by 20%, 31%, and 30%, respectively in serum of 12 months old rats in combination treatment group. The effect was more significant in 12 and 24 months old female rats with administration of estrogen and combined (EP) treatments. The results indirectly suggest that hormone replacement therapy (HRT) can reduce the risk of cardiovascular disease (CVD) thereby playing a cardio-protective role by restoring lipid and hormone levels to the similar levels as found in young female animals.
Biogerontology 02/2004; 5(6):411-9. · 3.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The solution structure of NKA, a decapeptide of mammalian origin, has been characterized by CD spectropolarimetry and 2D proton nuclear magnetic resonance (2D 1H-NMR) spectroscopy in both aqueous and membrane mimetic solvents. Unambiguous NMR assignments of protons have been made with the aid of correlation spectroscopy (DQF-COSY and TOCSY) experiments and nuclear Overhauser effect spectroscopy (NOESY and ROESY) experiments. The distance constraints obtained from the NMR data have been utilized to generate a family of structures, which have been refined using restrained energy minimization and dynamics. These data show that in water NKA prefers to be in an extended chain conformation whereas a helical conformation is induced in the central core and the C-terminal region (D4-M10) of the peptide in the presence of perdeuterated dodecylphosphocholine (DPC) micelles, a membrane model system. Though less defined the N-terminus also displays some degree of order and a possible turn structure. The conformation adopted by NKA in the presence of DPC micelles represents a structural motif typical of neurokinin-2 selective agonists and is similar to that reported for eledoisin in hydrophobic environment.
Biophysical Journal 01/2004; 85(6):4002-11. · 3.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Both the aqueous and the lipid-induced structure of eledoisin, an undecapeptide of mollusk origin, have been studied by two-dimensional proton nuclear magnetic resonance spectroscopy and distance geometry calculations. Unambiguous nuclear magnetic resonance assignments of protons have been made with the aid of correlation spectroscopy experiments and nuclear Overhauser effect spectroscopy experiments. The distance constraints obtained from the nuclear magnetic resonance data have been utilized in a distance geometry algorithm to generate a family of structures, which have been refined using restrained energy minimization and dynamics. These data show that, while in water and dimethyl sulfoxide, eledoisin prefers to be in an extended chain conformation, whereas in the presence of perdeuterated dodecylphosphocholine micelles, a membrane model system, helical conformation is induced in the central core and C-terminal region (K4-M11) of the peptide. N terminus, though less defined, also displays some degree of order and a possible turn structure. The conformation adopted by eledoisin in the presence of dodecylphosphocholine micelles is similar to the structural motif typical of neurokinin-2 selective agonists and with that reported for kassinin in hydrophobic environment.
Biophysical Journal 02/2003; 84(1):655-64. · 3.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The proximal portion of the C-terminus of the CB1 cannabinoid receptor is a primary determinant for G-protein activation. A 17 residue proximal C-terminal peptide (rodent CB1 401–417), the intracellular loop 4 (IL4) peptide, mimicked the receptor’s G-protein activation domain. Because of the importance of the cationic amino acids to G-protein activation, the three-dimensional structure of the IL4 peptide in a negatively charged sodium dodecyl sulfate (SDS) micellar environment has been studied by two-dimensional proton nuclear magnetic resonance (2D 1H NMR) spectroscopy and distance geometry calculations. Unambiguous proton NMR assignments were carried out with the aid of correlation spectroscopy (DQF-COSY and TOCSY) and nuclear Overhauser effect spectroscopy (NOESY and ROESY) experiments. The distance constraints were used in torsion angle dynamics algorithm for NMR applications (DYANA) to generate a family of structures which were refined using restrained energy minimization and dynamics. In water, the IL4 peptide prefers an extended conformation, whereas in SDS micelles, 310-helical conformation is induced. The predominance of 310-helical domain structure in SDS represents a unique difference compared with structure in alternative environments, which can significantly impact global electrostatic surface potential on the cytoplasmic surface of the CB1 receptor and might influence the signal to the G-proteins.
Journal of Structural Biology.
