Structural insights into photoactivation of plant Cryptochrome-2.

Cryptochromes (CRYs) are evolutionarily conserved photoreceptors that mediate various light-induced responses in bacteria, plants, and animals. Plant cryptochromes govern a variety of critical growth and developmental processes including seed germination, flowering time and entrainment of the circadian clock. CRY's photocycle involves reduction of their flavin adenine dinucleotide (FAD)-bound chromophore, which is completely oxidized in the dark and semi to fully reduced in the light signaling-active state. Despite the progress in characterizing cryptochromes, important aspects of their photochemistry, regulation, and light-induced structural changes remain to be addressed. In this study, we determine the crystal structure of the photosensory domain of Arabidopsis CRY2 in a tetrameric active state. Systematic structure-based analyses of photo-activated and inactive plant CRYs elucidate distinct structural elements and critical residues that dynamically partake in photo-induced oligomerization. Our study offers an updated model of CRYs photoactivation mechanism as well as the mode of its regulation by interacting proteins.

Crystal Structure Analysis of Great Cormorant (Phalacrocorax carbo) Hemoglobin to Understand its High Oxygen Affinity Characteristics by Special Structural Features.

BACKGROUND: Hemoglobin (Hb) subunits are composed of the specific functional prosthetic group "heme'' and a protein moiety "globin". Bird Hbs are functionally similar to mammalian Hbs but they are structurally dissimilar with mammalian. The insufficient structural studies on avian Hbs limit us to understand their degree of adaptation to such critical environments. The Great Cormorant (GCT) can fly and swim, the dual characteristic of GCT leads to study the sturcture of hemoglobin. OBJECTIVE: To determine the crystal structure of Great Cormorant Hemoglobin and to compare its three dimensional structure with other high and low oxygen affinity hemoglobin species to understand its characteristic features of high oxygen affinity. METHOD: The GCT hemoglobin has been purified, crystallized and data sets were processed using iMosflm. The integrated data has been solved using Molecular replacement method using Graylag hemoglobin (1FAW) as the template. The structure has been deposited in Protein Data Bank with PDB code: 3WR1. RESULTS: In order to characterize the tertiary and quaternary structural differences, the structure of cormorant hemoglobin is compared with GLG, BHG and human Hb. The larger variation observed between GCT and human Hb indicates that GCT Hb differs remarkably from human. The α1ß1 interface of Great cormorant Hb is similar to bar-headed goose Hb with few amino acid substitutions. It has been found that the interaction which is common among avian hemoglobins (α119 Pro- ß55Leu) is altered by Ala 119 in GCT. This intra-dimer contact (α119 Pro - ß 55 Leu) disruption leads to high oxygen affinity in BGH Hb. In cormorant, GLG and human the proline is unchanged but interestingly, in cormorant Hb, the ß55 position was found to be Thr instead of Leu. Similar kind of substitutions (ß 55 Leu - Ser) observed in Andean goose Hb structure leads to elevated oxygen affinity between Hb-O2. To our surprise, such type of substitution at ß 55 (Thr) in cormorant Hb confirms that it is comparable with Andean goose Hb structure. Thus the sequence, structural differences at alpha, beta heme pocket and interface contacts confirms that GCT adopts high oxygen affinity conformation. CONCLUSION: The three dimensional structure of Great cormorant hemoglobin has been investigated to understand its unique structural features to adopt during hypoxia condition. By comparing the sequence and overall structural similarities with high and low oxygen affinity species, it appears that GCT has more possibilities to subsist with low oxygen demand.

Structural insights into a multifunctional inhibitor, 'AMTIN' from tubers of Alocasia macrorrhizos and its possible role in dengue protease (NS2B-NS3) inhibition.

Protease inhibitors from plants play major role in defensive mechanism against various pathogenic organisms. AMTIN from the tubers of Alocasia macrorrhiza has been purified and characterized as multi-functional Kunitz type protease inhibitor. AMTIN is varied from other KTIs by having three different loops specific for binding to trypsin/amylase and subtilisin that are located approximately 30Ǻ away from one another as evidenced from crystallographic efforts. Biochemical studies on AMTIN reveal simultaneous binding of protease/amylase and have been cross validated using in-silico tools to model Amylase - AMTIN - Trypsin complex without any steric clashes. Apart from multi functionality, the remarkable structural and functional stability of AMTIN at high temperature, presence of many phosphorylation, myristoylation and glycosylation sites and molecular docking studies with dengue viral protease (NS2B-NS3) makes this protein interesting. Hence AMTIN can be considered as a template to design effective antivirals against dengue virus.

The nociceptin receptor (NOPR) and its interaction with clinically important agonist molecules: a membrane molecular dynamics simulation study.

The nociceptin receptor (NOPR) is an orphan G protein-coupled receptor that contains seven transmembrane helices. NOPR has a distinct mechanism of activation, though it shares a significant homology with other opioid receptors. Previously there have been reports on homology modeling of NOPR and also molecular dynamics simulation studies for a short period. Recently the crystal structure of NOPR was reported. In this study, we analyzed the time dependent behavior of NOPR docked with clinically important agonist molecules such as NOP (natural agonist) peptide and compound 10 (SCH-221510 derivative) using molecular dynamics simulations (MDS) for 100 ns. Molecular dynamics simulations of NOPR-agonist complexes allowed us to refine the system and to also identify stable structures with better binding modes. Structure activity relationships (SAR) for SCH221510 derivatives were investigated and reasons for the activities of these derivatives were determined. Our molecular dynamics trajectory analysis of NOPR-peptide and NOPR-compound 10 complexes found residues to be crucial for binding. Mutagenesis studies on the residues identified from our analysis could prove useful. Our results could also provide useful information in the structure-based drug design of novel and potent agonists targeting NOPR.

1'-Methyl-4'-phenyl-dispiro-[chromane-3,3'-pyrrolidine-2',3''-indoline]-2,2''-dione.

In the title compound, C(26)H(22)N(2)O(3), the pyrrolidine ring adopts an envelope conformation with the N atom as the flap. In the crystal, pairs of centrosymmetrically related mol-ecules are linked into dimers by N-H⋯O hydrogen bonds. In addition, there are C-H⋯O hydrogen bonds.