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Vinita Gupta

Publications and source records attributed to Vinita Gupta.

4 recordsLinked to original sources
PubMed2006

Lipid-induced extension of apolipoprotein E helix 4 correlates with low density lipoprotein receptor binding ability.

Apolipoprotein E (apoE) serves as a ligand for the low density lipoprotein receptor (LDLR) only when bound to lipid. The N-terminal domain of lipid-free apoE exists as globular 4-helix bundle that is conferred with LDLR recognition ability after undergoing a lipid binding-induced conformational change. To investigate the structural basis for this phenomenon, site-directed spin label electron paramagnetic resonance spectroscopy experiments were conducted, focusing on the region near the C-terminal end of helix 4 (Ala-164). Using C112S apoE-N-terminal as template, a series of single cysteine substitution variants (at sequence positions 161, 165, 169, 173, 176, and 181) were produced, isolated, and labeled with the nitroxide probe, methane thiosulfonate. Electron paramagnetic resonance analysis revealed that lipid association induced fixed secondary structure in a region of the molecule known to exist as random coil in the lipid-free state. In a complementary approach, site-directed fluorescence analysis using an environmentally sensitive probe indicated that the lipid-induced transition of this region of the protein to alpha helix was accompanied by relocation to a more hydrophobic environment. In studies with full-length apoE single Cys variants, a similar random coil to stable backbone transition was observed, consistent with the concept that lipid interaction induced an extension of helix 4 beyond the boundary defining its lipid-free conformation. This structural transition likely represents a key conformational change necessary for manifestation of the LDLR recognition properties of apoE.

Amino Acid Motifs↗
PubMed2003

Sphingosine-phosphate lyase enhances stress-induced ceramide generation and apoptosis.

Sphingosine-1-phosphate lyase is a widely expressed enzyme that catalyzes the essentially irreversible cleavage of the signaling molecule sphingosine 1-phosphate. To investigate whether sphingosine-1-phosphate lyase influences mammalian cell fate decisions, a recombinant human sphingosine-1-phosphate lyase fused to green fluorescent protein was expressed in HEK293 cells. The recombinant enzyme was active, localized to the endoplasmic reticulum, and reduced baseline sphingosine and sphingosine 1-phosphate levels. Stable overexpression led to diminished viability under stress, which was attributed to an increase in apoptosis and was reversible in a dose-dependent manner by exogenous sphingosine 1-phosphate. In contrast to sphingosine 1-phosphate, the products of the lyase reaction had no effect on apoptosis. Lyase enzymatic activity was required to potentiate apoptosis, because cells expressing a catalytically inactive enzyme behaved like controls. Stress increased the amounts of long- and very long-chain ceramides in HEK293 cells, and this was enhanced in cells overexpressing wild type but not catalytically inactive lyase. The ceramide increases appeared to be required for apoptosis, because inhibition of ceramide synthase with fumonisin B1 decreased apoptosis in lyase-overexpressing cells. Thus, sphingosine-1-phosphate lyase overexpression in HEK293 cells decreases sphingosine and sphingosine 1-phosphate amounts but elevates stress-induced ceramide generation and apoptosis. This identifies sphingosine-1-phosphate lyase as a dual modulator of sphingosine 1-phosphate and ceramide metabolism as well as a regulator of cell fate decisions and, hence, a potential target for diseases with an imbalance in these biomodulators, such as cancer.

Aldehyde-Lyases↗
PubMedDate not supplied

Posterior continuous curvilinear capsulorhexis with and without optic capture of the posterior chamber intraocular lens in the absence of vitrectomy.

PURPOSE: To evaluate the efficacy of posterior continuous curvilinear capsulorhexis (PCCC) with optic capture of the posterior chamber intraocular lens (PC IOL) in the absence of vitrectomy in preventing secondary opacification of the visual axis following pediatric cataract surgery. PATIENTS AND METHODS: Thirty-four eyes of 28 children with congenital or developmental cataract, aged 1.5 to 12 years (mean, 6.39 years), were included in this prospective, randomized study. Anterior continuous curvilinear capsulorhexis (ACCC) with PCCC without optic capture of the PC IOL was performed in group A (18 eyes) and ACCC with PCCC with optic capture of the PC IOL was performed in group B (16 eyes). None of the eyes underwent anterior vitrectomy. Secondary opacification of the visual axis, visual acuity, and possible complications were observed and analyzed. RESULTS: The follow-up period ranged from 8 to 28 months (mean, 17.5 months). All 16 eyes (100%) in group B had a clear visual axis at the end of follow-up. Eight eyes (44.4%) in group A had significant opacification of the visual axis. The difference between the two groups was statistically significant (P = .0011). No eye in group B required secondary intervention, whereas all 8 eyes in group A with significant secondary opacification required secondary intervention. There was no statistically significant difference in other complications such as anterior chamber reaction, fibrin formation, lenticular precipitates, and posterior synechiae. The final best-corrected visual acuity at the end of follow-up was comparable in the two groups (P > .05). CONCLUSION: PCCC with optic capture of the PC IOL prevents secondary opacification of the visual axis even in the absence of vitrectomy.

Capsulorhexis↗