NISCAIR Online Periodicals Repository Collection: IJC-A Vol.50A(03-04) [March-April 2011]

Structural basis for preferential Ca²⁺-displacement by a paramagnetic ion (Ce³⁺) in non-myristoylated neuronal calcium sensor-1

Title: Structural basis for preferential Ca²⁺-displacement by a paramagnetic ion (Ce³⁺) in non-myristoylated neuronal calcium sensor-1

Authors: Chandra, Kousik; Susmitha, A L; Sharma, Y; Chary, K V R

Abstract: We have investigated the Ca²⁺-displacement by a trivalent lanthanide ion (Ce³⁺) in a Ca²⁺-sensor protein called neuronal calcium sensor-1 in its non-myristoylated form by NMR. We observe that all the Ca²⁺ bound to the three active Ca²⁺-binding loops are displaced by Ce³⁺. Microscopically, NMR paramagnetic titration data on [Ca²⁺]-non-myr-NCS-1 shows that the Ce³⁺ displaces Ca²⁺ first from both sites, EF2 and EF3, almost in parallel, followed by the displacement from EF4. Between EF2 and EF3, the NMR data conclusively shows that the Ca²⁺-displacement is more prominent in EF2 as compared to that in EF3. These findings have been attributed to: (i) the presence of a higher number of negatively charged residues in EF2 compared to EF3 and EF4, and, (ii) the presence of a Lys instead of a highly conserved Phe at –4 position in the first Ca²⁺-binding loop, which results in a relatively more open conformation of the N-terminal domain compared to the C-terminal counterpart.

Page(s): 539-547

Chromium(III) mediated conformational changes associated with alterations in the enzymatic activity of BSA: Influence of the coordinated ligand

Title: Chromium(III) mediated conformational changes associated with alterations in the enzymatic activity of BSA: Influence of the coordinated ligand

Authors: Raja, Natesasn Sella; Shrivastava, H Yamini; Nair, Balachandran Unni

Abstract: Interaction of three chromium(III) complexes, [Cr(salen)(H₂O)₂]ClO₄(1), Na[Cr(EDTA)(H₂O)] (2) and [Cr(en)₃]Cl₃ (3) with bovine serum albumin (BSA) has been investigated in order to understand the role of coordinated ligand in mediating the interaction between the protein and chromium(III) ion. Binding of (1) and (2) to BSA has been found to result in increase in the esterase activity of BSA from 2.41 to 2.72 and 2.62 U/L respectively. On the other hand, binding of (3) results in decrease of the activity from 2.41 to 1.91 U/L. These changes in the esterase activity are also reflected in the conformation of BSA in the presence of (1), (2) and (3). CD spectrum of BSA clearly indicates that binding of (1) and (2) leads to increase in the helicity of BSA, whereas binding of (3) leads to decrease in the helicity of the protein. Such a change in the helicity of BSA leads to change in the orientation of active amino acids (Tyr ₄₁₁ and Arg ₄₁₀) in the protein, thus affecting the esterase activity of protein. The nature of the coordinated ligand has also been found to influence the stability of BSA against trypsin digestion.

Page(s): 531-538

Photocytotoxicity and DNA photocleavage activity of La(III) and Gd(III) complexes of phenanthroline bases

Title: Photocytotoxicity and DNA photocleavage activity of La(III) and Gd(III) complexes of phenanthroline bases

Authors: Hussain, Akhtar; Saha, Sounik; Majumdar, Ritankar; Dighe, Rajan R; Chakravarty, Akhil R

Abstract: Lanthanide(III) complexes [La(B)(acac)₃] (1–3) and [Gd(B)(acac)₃] (4–6), whereB is a N,N-donor phenanthroline base, viz., 1,10-phenanthroline (phen in 1, 4), dipyrido[3,2-d:2ʹ,3ʹ-f]quinoxaline (dpq in 2, 5) and dipyrido[3,2-a:2ʹ,3ʹ-c]phenazine (dppz in 3, 6), have been prepared and characterized. The Gd(III) complexes 4 – 6 are structurally characterized by single crystal X-ray crystallography. The complexes display GdO₆N₂ coordination with the ligands showing bidentate chelating mode of bonding. The complexes are non-electrolytic in aqueous DMF and exhibit ligand-centered absorption bands in the UV region. The dppz complexes show a band at 380 nm in DMF. The La(III) complexes are diamagnetic. The Gd(III) complexes are paramagnetic with magnetic moment that corresponds to seven unpaired electrons. The complexes are avid binders to calf thymus DNA giving K_b values in the range of 4.7 x 10⁴- 6.1 x 10⁵ M^-1 with a relative binding order: 3, 6 (dppz) > 2, 5 (dpq) > 1, 4 (phen). The binding data suggest DNA surface and/or groove binding nature of the complexes. The dpq and dppz complexes efficiently cleave SC DNA to its nicked circular form in UV-A light of 365 nm via formation of both singlet oxygen (¹O₂) and hydroxyl radical (HO^●) species. The dppz complexes 3 and 6 exhibit significant PDT effect in HeLa cervical cancer cells giving respective IC₅₀ value of 460(±50) and 530(±30) nM in UV-A light of 365 nm, and are essentially non-toxic in dark with an IC₅₀ value of >100 M. The dppz ligand alone is cytotoxic in dark and UV-A light. A significant decrease in the dark toxicity of the dppz base is observed on binding to the Ln(III) ion while retaining its photocytotoxicity.

Page(s): 519-530

A comparative study of third-order optical nonlinearity of symmetrical dipolar chromogenic probes and their enhancement by different metal ions

Title: A comparative study of third-order optical nonlinearity of symmetrical dipolar chromogenic probes and their enhancement by different metal ions

Authors: Jana, Atanu; Lim, Jong Min; Park, Sun Woo; Kim, Dongho; Bharadwaj, Parimal K

Abstract: We have investigated the two-photon absorption properties of three symmetrical NLO-phores, L₁, L₂ and L₃, having different conjugation lengths as well as different binding sites like cryptand, crown ether and bipyridyl moiety. The TPA properties have been measured by a femtosecond laser at 800 nm, which is in the window of ‘in vivo’ imaging. Upon metal ion binding, the TPA cross-section values are enhanced to different extents depending on the nature of metal ion and the overall architecture of the molecular system as well. The unique CT transition process after metal ion incorporation, along with various conjugation lengths of the NLO-phores, fully elucidates the structure-property relationship of the photophysical properties.

Page(s): 511-518

NISCAIR Online Periodicals Repository Collection: IJC-A Vol.50A(03-04) [March-April 2011]

Structural basis for preferential Ca2+-displacement by a paramagnetic ion (Ce3+) in non-myristoylated neuronal calcium sensor-1

Chromium(III) mediated conformational changes associated with alterations in the enzymatic activity of BSA: Influence of the coordinated ligand

Photocytotoxicity and DNA photocleavage activity of La(III) and Gd(III) complexes of phenanthroline bases

A comparative study of third-order optical nonlinearity of symmetrical dipolar chromogenic probes and their enhancement by different metal ions

Structural basis for preferential Ca²⁺-displacement by a paramagnetic ion (Ce³⁺) in non-myristoylated neuronal calcium sensor-1