Genome-wide identification and expression analysis of sucrose synthase genes in allotetraploid Brassica juncea.

Sucrose plays pivotal role in energy metabolism and regulating gene expression of several physiological processes in higher plants. Here, fourteen sucrose synthase (SUS) genes have been identified in the allotetraploid genome of Indian mustard, Brassica juncea. The identified SUS genes in B. juncea (BjSUS) were derived from the two-progenitor species, B. rapa and B. nigra. Intron-exon analysis indicated loss or gain of 1-3 introns in diversification of SUS gene family. Phylogenetic analysis revealed discrete evolutionary paths for the BjSUS genes, originating from three ancestor groups, SUS I, SUS II and SUS III. Gene expression study revealed significant variability in expression of the BjSUS paralogs across the different tissues. BjSUS genes showed transcriptional activation in response to defense hormones and a late response to wounding. Tissue and temporal specificity of expression revealed importance of specific SUS paralogs at different developmental stages and under different stress conditions. The study highlighted differential involvement of SUS paralogs in sucrose metabolism across the tissues and stress-responses, in a major oilseed crop B. juncea.

Strength, Stability, and cis-Motifs of In silico Identified Phloem-Specific Promoters in Brassica juncea (L.).

Aphids, a hemipteran group of insects pose a serious threat to many of the major crop species including Brassica oilseeds. Transgenic strategies for developing aphid-resistant plant types necessitate phloem-bound expression of the insecticidal genes. A few known phloem-specific promoters, in spite of tissue-specific activity fail to confer high level gene-expression. Here, we identified seven orthologues of phloem-specific promoters in B. juncea (Indian mustard), and experimentally validated their strength of expression in phloem exudates. Significant cis-motifs, globally occurring in phloem-specific promoters showed variable distribution frequencies in these putative phloem-specific promoters of B. juncea. In RT-qPCR based gene-expression study promoter of Glutamine synthetase 3A (GS3A) showed multifold higher activity compared to others, across the different growth stages of B. juncea plants. A statistical method employing four softwares was devised for rapidly analysing stability of the promoter-activities across the plant developmental stages. Different statistical softwares ranked these B. juncea promoters differently in terms of their stability in promoter-activity. Nevertheless, the consensus in output empirically suggested consistency in promoter-activity of the six B. juncea phloem- specific promoters including GS3A. The study identified suitable endogenous promoters for high level and consistent gene-expression in B. juncea phloem exudate. The study also demonstrated a rapid method of assessing species-specific strength and stability in expression of the endogenous promoters.

Efficacy and safety of autologous cultured melanocytes delivered on poly (DL-lactic acid) film: a prospective, open-label, randomized, multicenter study.

BACKGROUND: Small vitiliginous patches have been treated with epidermal grafts or their cell suspensions. In an attempt to overcome some of the shortcomings of cell suspension delivery, we have delivered melanocytes on a polymeric film. OBJECTIVES: To evaluate the clinical effectiveness of a cultured graft consisting of autologous cultured melanocytes on a poly (DL-lactic acid) (PLA) film in subjects with stable vitiligo. METHODS: A prospective open-label, randomized, multicenter clinical trial was conducted with 22 patients. Each subject was treated with cultured graft and polyurethane dressing (control arm) after epidermal ablation and followed for up to 9 months. The extent of repigmentation in the treated sites was compared with that control sites at days 90, 180, and 270. RESULTS: In the treatment arm, a minimum of 70% repigmentation was observed in five subjects at day 90; nine at day 180, and 10 at day 270. In the control arm, only one subject showed repigmentation until day 270. None of the test sites reported any recurrence of vitiliginous patches by the end of the study. CONCLUSIONS: Cultured melanocytes delivered on PLA film were efficacious and safe when applied on patients with stable vitiligo.

Speeding up proton transfer in a fast enzyme: kinetic and crystallographic studies on the effect of hydrophobic amino acid substitutions in the active site of human carbonic anhydrase II.

Catalysis of the hydration of CO2 by human carbonic anhydrase isozyme II (HCA II) is sustained at a maximal catalytic turnover of 1 mus-1 by proton transfer between a zinc-bound solvent and bulk solution. This mechanism of proton transfer is facilitated via the side chain of His64, which is located 7.5 A from the zinc, and mediated via intervening water molecules in the active-site cavity. Three hydrophilic residues that have previously been shown to contribute to the stabilization of these intervening waters were replaced with hydrophobic residues (Y7F, N62L, and N67L) to determine their effects on proton transfer. The structures of all three mutants were determined by X-ray crystallography, with crystals equilibrated from pH 6.0 to 10.0. A range of changes were observed in the ordered solvent and the conformation of the side chain of His64. Correlating these structural variants with kinetic studies suggests that the very efficient proton transfer (approximately 7 micros-1) observed for Y7F HCA II in the dehydration direction, compared with the wild type and other mutants of this study, is due to a combination of three features. First, in this mutant, the side chain of His64 showed an appreciable inward orientation pointing toward the active-site zinc. Second, in the structure of Y7F HCA II, there is an unbranched chain of hydrogen-bonded waters linking the proton donor His64 and acceptor zinc-bound hydroxide. Finally, the difference in pKa of the donor and acceptor appears favorable for proton transfer. The data suggest roles for residues 7, 62, and 67 in fine-tuning the properties of His64 for optimal proton transfer in catalysis.

Location of binding sites in small molecule rescue of human carbonic anhydrase II.

Small molecule rescue of mutant forms of human carbonic anhydrase II (HCA II) occurs by participation of exogenous donors/acceptors in the proton transfer pathway between the zinc-bound water and solution. To examine more thoroughly the energetics of this activation, we have constructed a mutant, H64W HCA II, which we have shown is activated by 4-methylimidazole (4-MI) by a mechanism involving the binding of 4-MI to the side chain of Trp-64 approximately 8 A from the zinc. A series of experiments are consistent with the activation of H64W HCA II by the interaction of imidazole and pyridine derivatives as exogenous proton donors with the indole ring of Trp-64; these experiments include pH profiles and H/D solvent isotope effects consistent with proton transfer, observation of approximately fourfold greater activation with the mutant containing Trp-64 compared with Gly-64, and the observation by x-ray crystallography of the binding of 4-MI associated with the indole side chain of Trp-64 in W5A-H64W HCA II. Proton donors bound at the less flexible side chain of Trp-64 in W5A-H64W HCA II do not show activation, but such donors bound at the more flexible Trp-64 of H64W HCA II do show activation, supporting suggestions that conformational mobility of the binding site is associated with more efficient proton transfer. Evaluation using Marcus theory showed that the activation of H64W HCA II by these proton donors was reflected in the work functions w(r) and w(p) rather than in the intrinsic Marcus barrier itself, consistent with the role of solvent reorganization in catalysis.

Complex determinants in human immunodeficiency virus type 1 envelope gp120 mediate CXCR4-dependent infection of macrophages.

Host cell range, or tropism, combined with coreceptor usage defines viral phenotypes as macrophage tropic using CCR5 (M-R5), T-cell-line tropic using CXCR4 (T-X4), or dually lymphocyte and macrophage tropic using CXCR4 alone or in combination with CCR5 (D-X4 or D-R5X4). Although envelope gp120 V3 is necessary and sufficient for M-R5 and T-X4 phenotypes, the clarity of V3 as a dominant phenotypic determinant diminishes in the case of dualtropic viruses. We evaluated D-X4 phenotype, pathogenesis, and emergence of D-X4 viruses in vivo and mapped genetic determinants in gp120 that mediate use of CXCR4 on macrophages ex vivo. Viral quasispecies with D-X4 phenotypes were associated significantly with advanced CD4+-T-cell attrition and commingled with M-R5 or T-X4 viruses in postmortem thymic tissue and peripheral blood. A D-X4 phenotype required complex discontinuous genetic determinants in gp120, including charged and uncharged amino acids in V3, the V5 hypervariable domain, and novel V1/V2 regions distinct from prototypic M-R5 or T-X4 viruses. The D-X4 phenotype was associated with efficient use of CXCR4 and CD4 for fusion and entry but unrelated to levels of virion-associated gp120, indicating that gp120 conformation contributes to cell-specific tropism. The D-X4 phenotype describes a complex and heterogeneous class of envelopes that accumulate multiple amino acid changes along an evolutionary continuum. Unique gp120 determinants required for the use of CXCR4 on macrophages, in contrast to cells of lymphocytic lineage, can provide targets for development of novel strategies to block emergence of X4 quasispecies of human immunodeficiency virus type 1.

Proton transfer in a Thr200His mutant of human carbonic anhydrase II.

Human carbonic anhydrase II (HCA II) has a histidine at position 64 (His64) that donates a proton to the zinc-bound hydroxide in catalysis of the dehydration of bicarbonate. To examine the effect of the histidine location on proton shuttling, His64 was replaced with Ala and Thr200 replaced with histidine (H64A-T200H HCAII), effectively relocating the proton shuttle residue 2 A closer to the zinc-bound hydroxide compared to wild type HCA II. The crystal structure of H64A-T200H HCA II at 1.8 A resolution shows the side chain of His200 directly hydrogen-bonded with the zinc-bound solvent. Different proton transfer processes were observed at pH 6 and at pH 8 during the catalytic hydration-dehydration cycle, measured by mass spectrometry as the depletion of 18O from C18O2 by H64A-T200H HCA II. The process at pH 6.0 is attributed to proton transfer between the side chain of His200 and the zinc-bound hydroxide, in analogy with proton transfer involving His64 in wild-type HCA II. At pH 8.0 it is attributed to proton transfer between bicarbonate and the zinc-bound hydroxide, as supported by the dependence of the rate of proton transfer on bicarbonate concentration and on solvent hydrogen isotope effects. This study establishes that a histidine directly hydrogen-bonded to the zinc-bound hydroxide, can adopt the correct distance geometry to support proton transfer

Manipulating the length of the b subunit F1 binding domain in F1F0 ATP synthase from Escherichia coli.

The peripheral stalk of F(1)F(0) ATP synthase is composed of a parallel homodimer of b subunits that extends across the cytoplasmic membrane in F(0) to the top of the F(1) sector. The stalk serves as the stator necessary for holding F(1) against movement of the rotor. A series of insertions and deletions have been engineered into the hydrophilic domain that interacts with F(1). Only the hydrophobic segment from val-121 to ala-132 and the extreme carboxyl terminus proved to be highly sensitive to mutation. Deletions in either site apparently abolished enzyme function as a result of defects is assembly of the F(1)F(0) complex. Other mutations manipulating the length of the sequence between these two areas had only limited effects on enzyme function. Expression of a b subunit with insertions with as few as two amino acids into the hydrophobic segment also resulted in loss of F(1)F(0) ATP synthase. However, a fully defective b subunit with seven additional amino acids could be stabilized in a heterodimeric peripheral stalk within a functional F(1)F(0) complex by a normal b subunit.

Mutagenesis studies of the F1F0 ATP synthase b subunit membrane domain.

A homodimer of b subunits constitutes the peripheral stalk linking the F1 and F0 sectors of the Escherichia coli ATP synthase. Each b subunit has a single-membrane domain. The constraints on the membrane domain have been studied by systematic mutagenesis. Replacement of a segment proximal to the cytoplasmic side of the membrane had minimal impact on F1F0 ATP synthase. However, multiple substitutions on the periplasmic side resulted in defects in assembly of the enzyme complex. These mutants had insufficient oxidative phosphorylation to support growth, and biochemical studies showed little F1F0 ATPase and no detectable ATP-driven proton pumping activity. Expression of the b(N2A,T6A,Q10A) subunit was also oxidative phosphorylation deficient, but the b(N2A,T6A,Q10A) protein was incorporated into an F1F0 complex. Single amino acid substitutions had minimal reductions in F1F0 ATP synthase function. The evidence suggests that the b subunit membrane domain has several sites of interaction contributing to assembly of F0, and that these interactions are strongest on the periplasmic side of the bilayer.