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1.  Structural Investigation of a Novel N-Acetyl Glucosamine Binding Chi-Lectin Which Reveals Evolutionary Relationship with Class III Chitinases 
PLoS ONE  2013;8(5):e63779.
The glycosyl hydrolase 18 (GH18) family consists of active chitinases as well as chitinase like lectins/proteins (CLPs). The CLPs share significant sequence and structural similarities with active chitinases, however, do not display chitinase activity. Some of these proteins are reported to have specific functions and carbohydrate binding property. In the present study, we report a novel chitinase like lectin (TCLL) from Tamarindus indica. The crystal structures of native TCLL and its complex with N-acetyl glucosamine were determined. Similar to the other CLPs of the GH18 members, TCLL lacks chitinase activity due to mutations of key active site residues. Comparison of TCLL with chitinases and other chitin binding CLPs shows that TCLL has substitution of some chitin binding site residues and more open binding cleft due to major differences in the loop region. Interestingly, the biochemical studies suggest that TCLL is an N-acetyl glucosamine specific chi-lectin, which is further confirmed by the complex structure of TCLL with N-acetyl glucosamine complex. TCLL has two distinct N-acetyl glucosamine binding sites S1 and S2 that contain similar polar residues, although interaction pattern with N-acetyl glucosamine varies extensively among them. Moreover, TCLL structure depicts that how plants utilize existing structural scaffolds ingenuously to attain new functions. To date, this is the first structural investigation of a chi-lectin from plants that explore novel carbohydrate binding sites other than chitin binding groove observed in GH18 family members. Consequently, TCLL structure confers evidence for evolutionary link of lectins with chitinases.
PMCID: PMC3662789  PMID: 23717482
2.  Expression, purification, crystallization and preliminary crystallographic studies of cis-biphenyl-2,3-dihydrodiol-2,3-dehydrogenase from Pandoraea pnomenusa B-356 
A 29 kDa cis-biphenyl-2,3-dihydrodiol-2,3-dehydrogenase from P. pnomenusa B-356 was purified, crystallized and characterized by the X-ray diffraction method.
cis-Biphenyl-2,3-dihydrodiol-2,3-dehydrogenase (BphB) is involved in the aerobic biodegradation of biphenyl and polychlorinated biphenyls. BphB from Pandoraea pnomenusa strain B-356 was overexpressed in Escherichia coli, purified to homogeneity and crystallized. Crystals were obtained by the sitting-drop vapour-diffusion method using polyethylene glycol 3350 and 0.2 M sodium malonate. A BphB crystal diffracted to 2.8 Å resolution and belonged to space group P43212, with unit-cell parameters a = b = 75.2, c = 180.4 Å. Preliminary crystallographic analysis indicated the presence of two molecules in the asymmetric unit, giving a Matthews coefficient of 2.2 Å3 Da−1 and a solvent content of 44%.
PMCID: PMC3001663  PMID: 21045310
cis-biphenyl-2,3-dihydrodiol-2,3-dehydrogenase; Pandoraea pnomenusa; biodegradation
3.  Structure-Function Studies of DNA Binding Domain of Response Regulator KdpE Reveals Equal Affinity Interactions at DNA Half-Sites 
PLoS ONE  2012;7(1):e30102.
Expression of KdpFABC, a K+ pump that restores osmotic balance, is controlled by binding of the response regulator KdpE to a specific DNA sequence (kdpFABCBS) via the winged helix-turn-helix type DNA binding domain (KdpEDBD). Exploration of E. coli KdpEDBD and kdpFABCBS interaction resulted in the identification of two conserved, AT-rich 6 bp direct repeats that form half-sites. Despite binding to these half-sites, KdpEDBD was incapable of promoting gene expression in vivo. Structure-function studies guided by our 2.5 Å X-ray structure of KdpEDBD revealed the importance of residues R193 and R200 in the α-8 DNA recognition helix and T215 in the wing region for DNA binding. Mutation of these residues renders KdpE incapable of inducing expression of the kdpFABC operon. Detailed biophysical analysis of interactions using analytical ultracentrifugation revealed a 2∶1 stoichiometry of protein to DNA with dissociation constants of 200±100 and 350±100 nM at half-sites. Inactivation of one half-site does not influence binding at the other, indicating that KdpEDBD binds independently to the half-sites with approximately equal affinity and no discernable cooperativity. To our knowledge, these data are the first to describe in quantitative terms the binding at half-sites under equilibrium conditions for a member of the ubiquitous OmpR/PhoB family of proteins.
PMCID: PMC3264566  PMID: 22291906
4.  Crystallization and preliminary X-ray diffraction analysis of the complex of Kunitz-type tamarind trypsin inhibitor and porcine pancreatic trypsin 
A complex of tamarind trypsin inhibitor with porcine trypsin was crystallized and analyzed by X-ray diffraction.
The complex of Tamarindus indica Kunitz-type trypsin inhibitor and porcine trypsin has been crystallized by the sitting-drop vapour-diffusion method using ammonium acetate as precipitant and sodium acetate as buffer. The homogeneity of complex formation was checked by size-exclusion chromatography and further confirmed by reducing SDS–PAGE. The crystals diffracted to 2.0 Å resolution and belonged to the tetragonal space group P41, with unit-cell parameters a = b = 57.1, c = 120.1 Å. Preliminary X-ray diffraction analysis indicated the presence of one unit of inhibitor–trypsin complex per asymmetric unit, with a solvent content of 45%.
PMCID: PMC2777053  PMID: 19923745
tamarind trypsin inhibitor; porcine pancreatic trypsin; Kunitz-type inhibitors
5.  Purification, crystallization and preliminary crystallographic studies of a Kunitz-type proteinase inhibitor from tamarind (Tamarindus indica) seeds 
A 21 kDa Kunitz-type proteinase inhibitor was purified from tamarind (T. indica) seeds, crystallized and characterized by X-ray diffraction.
A Kunitz-type proteinase inhibitor has been purified from tamarind (Tamarindus indica) seeds. SDS–PAGE analysis of a purified sample showed a homogeneous band corresponding to a molecular weight of 21 kDa. The protein was identified as a Kunitz-type proteinase inhibitor based on N-terminal amino-acid sequence analysis. It was crystallized by the vapour-diffusion method using PEG 6000. The crystals belonged to the orthorhombic space group C2221, with unit-cell parameters a = 37.2, b = 77.1, c = 129.1 Å. Diffraction data were collected to a resolution of 2.7 Å. Preliminary crystallographic analysis indicated the presence of one proteinase inhibitor molecule in the asymmetric unit, with a solvent content of 44%.
PMCID: PMC2705649  PMID: 19574654
Kunitz-type proteinase inhibitors; Tamarindus indica
6.  Isolation, purification, crystallization and preliminary crystallographic studies of chitinase from tamarind (Tamarindus indica) seeds 
A 34 kDa chitinase from tamarind (T. indica) seeds was purified, crystallized and characterized using X-ray diffraction.
A protein with chitinase activity has been isolated and purified from tamarind (Tamarindus indica) seeds. N-terminal amino-acid sequence analysis of this protein confirmed it to be an ∼34 kDa endochitinase which belongs to the acidic class III chitinase family. The protein was crystallized by the vapour-diffusion method using PEG 4000. The crystals belonged to the tetragonal space group P41, with two molecules per asymmetric unit. Diffraction data were collected to a resolution of 2.6 Å.
PMCID: PMC2664755  PMID: 19342775
chitinases; Tamarindus indicus

Results 1-6 (6)