Razia Tajwar - Academia.edu (original) (raw)

Papers by Razia Tajwar

bioRxiv, 2022

Hepatitis B virus (HBV) replicates by protein-primed reverse transcription. It chronically infect... more Hepatitis B virus (HBV) replicates by protein-primed reverse transcription. It chronically infects >250 million people, and the dominant anti-HBV drugs are nucleos(t)ide analogs targeting the viral polymerase (P). P has four domains, the terminal protein (TP) that primes DNA synthesis, a spacer, the reverse transcriptase (RT), and the ribonuclease H (RNaseH). Despite being a major drug target and catalyzing a reverse transcription pathway very different from the retroviral pathway, HBV P has resisted structural analysis for decades. Here, we exploited advances in protein structure prediction to model the structure of P. The predicted HBV RT and RNaseH domains aligned to the HIV RT-RNaseH at 3.75 Å RMSD, had a nucleic acid binding groove spanning the two active sites, had DNA polymerase active site motifs in their expected positions, and accommodated two Mg++ ions in both active sites. Surprisingly, the TP domain wrapped around the RT domain, with the priming tyrosine poised over ...

Journal of Biotechnology, 2019

Using multi-step error prone PCR (ep-PCR) of the gene encoding endoglucanase Cel12A (27 kDa) from... more Using multi-step error prone PCR (ep-PCR) of the gene encoding endoglucanase Cel12A (27 kDa) from Thermotoga neapolitana, mutants were obtained with many fold increase in the enzyme activity. The best mutant (C6, N47S/E57 K/ V88A/S157 P/K165 H) obtained after four rounds of ep-PCR showed 2.7−, 5− and 4.8−fold increase in activity against CMC, RAC and Avicel, respectively, compared with the wild type enzyme. The other characteristics of the mutated enzyme with respect to stability, optimum working pH and temperature were comparable to the wild type enzyme.C6 mutant showed higher binding efficiency towards the rice straw (∼50%) than the wild type (∼41%). The structural information obtained from the protein docking of the wild type Cel12A and its mutant showed that E57 K improved the binding affinity between enzyme and ligand by producing conformational changes in the catalytic cavity. The other mutations can facilitate the enzyme-substrate binding interactions to enhance catalytic activity although they are not directly involved in catalysis. The wild type and mutant enzyme produce cellobiose as the major products for both soluble and insoluble substrates, suggesting that this enzyme should be a cellobiohydrolase instead of endoglucanase as previously reported.

Extremophiles : life under extreme conditions, Jan 23, 2017

A novel, family GH10 enzyme, Xyn10B from Acidothermus cellulolyticus 11B was cloned and expressed... more A novel, family GH10 enzyme, Xyn10B from Acidothermus cellulolyticus 11B was cloned and expressed in Escherichia coli. This enzyme was purified to homogeneity by binding to regenerated amorphous cellulose. It had higher binding on Avicel as compared to insoluble xylan due to the presence of cellulose-binding domains, CBM3 and CBM2. This enzyme was optimally active at 70 °C and pH 6.0. It was stable up to 70 °C while the CD spectroscopy analysis showed thermal unfolding at 80 °C. Xyn10B was found to be a trifunctional enzyme having endo-xylanase, arabinofuranosidase and acetyl xylan esterase activities. Its activities against beechwood xylan, p-Nitrophenyl arabinofuranoside and p-Nitrophenyl acetate were found to be 126,480, 10,350 and 17,250 U μmol-1, respectively. Xyn10B was highly active producing xylobiose and xylose as the major end products, as well as debranching the substrates by removing arabinose and acetyl side chains. Due to its specific characteristics, this enzyme seems...

Enzyme and microbial technology, 2017

Xylanase XynB of the hyperthermophile Thermotoga maritima, which belongs to glycoside hydrolase f... more Xylanase XynB of the hyperthermophile Thermotoga maritima, which belongs to glycoside hydrolase family 10 (GH10), does not have an associated carbohydrate binding module (CBM) in the native state. CBM6 and CBM22 from a thermophile Clostridium thermocellum were fused to the catalytic domain of XynB (XynB-C) to determine the effects on activity and other properties. XynB-B22C and XynB-CB22, produced by fusing CBM22 to the N- and C-terminal of XynB-C, showed 1.7- and 3.24-fold increase in activity against the insoluble birchwood xylan, respectively. Similarly, CBM6 when attached to the C-terminal of XynB-C resulted in 2.0-fold increase in activity, whereas its attachment to the N-terminal did not show any increase of activity. XynB-B22C and XynB-CB22 retained all the activity, whereas XynB-B6C and XynB-CB6 lost 17 and 11% of activity, respectively, at 60°C for 4h. Thermostability data and the secondary structure contents obtained by molecular modelling are in agreement with the data fr...