Recombinant Expression and Characterization of Lemon (Citrus limon) Peroxidase

BACKGROUND

Class III plant peroxidases play important role in a number of physiological processes in plants such as lignin biosynthesis, suberization, cell wall biosynthesis, reactive oxygen species metabolism and plant defense against pathogens. Peroxidases are also of significance in several industrial applications. In view of this, the production and identification of novel peroxidases having resistance towards temperature, pH, salts is desirable.

OBJECTIVE

The objective of the present work was to clone and characterize a novel plant peroxidase suitable for industrial application.

METHODS

A full length cDNA clone of lemon peroxidase was isolated using PCR and RACE approaches, characterized and heterologously expressed in Escherichia coli using standard protocols. The expressed peroxidase was purified using Ni-NTA agarose column and biochemically characterized using standard protocols. The peroxidase was also in-silico characterized at nucleotide as well as protein levels using standard protocols.

RESULTS

A full length cDNA clone of lemon peroxidase was isolated and expressed heterologously in E. coli. The expressed recombinant lemon peroxidase (LPRX) was activated by in-vitro refolding and purified. The purified LPRX exhibited pH and temperature optima of pH 7.0 and 50°C, respectively. The LPRX was found to be activated by metal ions (Na+, Ca2+, Mg2+ and Mn2+) at lower concentration. The expressional analysis of the transcripts suggested involvement of lemon peroxidase in plant defense. The lemon peroxidase was in silico modelled and docked with the substrates guaiacol, and pyrogallol and shown the favourability of pyrogallol over guaiacol, which is in agreement with the in-vitro findings. The protein function annotation analyses suggested the involvement of lemon peroxidase in the phenylpropanoid biosynthesis pathway and plant defense mechanisms.

CONCLUSION

Based on the biochemical characterization, the purified peroxidase was found to be resistant towards the salts and thus, might be a good candidate for industrial exploitation. The in-silico protein function annotation and transcript analyses highlighted the possible involvement of the lemon peroxidase in plant defense response.

In-Silico Characterization of Glycosyl Hydrolase Family 1 β-Glucosidase from Trichoderma asperellum UPM1

β-glucosidases (Bgl) are widely utilized for releasing non-reducing terminal glucosyl residues. Nevertheless, feedback inhibition by glucose end product has limited its application. A noticeable exception has been found for β-glucosidases of the glycoside hydrolase (GH) family 1, which exhibit tolerance and even stimulation by glucose. In this study, using local isolate Trichoderma asperellum UPM1, the gene encoding β-glucosidase from GH family 1, hereafter designated as TaBgl2, was isolated and characterized via in-silico analyses. A comparison of enzyme activity was subsequently made by heterologous expression in Escherichia coli BL21(DE3). The presence of N-terminal signature, cis-peptide bonds, conserved active site motifs, non-proline cis peptide bonds, substrate binding, and a lone conserved stabilizing tryptophan (W) residue confirms the identity of Trichoderma sp. GH family 1 β-glucosidase isolated. Glucose tolerance was suggested by the presence of 14 of 22 known consensus residues, along with corresponding residues L167 and P172, crucial in the retention of the active site's narrow cavity. Retention of 40% of relative hydrolytic activity on ρ-nitrophenyl-β-D-glucopyranoside (ρNPG) in a concentration of 0.2 M glucose was comparable to that of GH family 1 β-glucosidase (Cel1A) from Trichoderma reesei. This research thus underlines the potential in the prediction of enzymatic function, and of industrial importance, glucose tolerance of family 1 β-glucosidases following relevant in-silico analyses.

Association of a homozygous GCK missense mutation with mild diabetes

Background

Homozygous inactivating GCK mutations have been repeatedly reported to cause severe hyperglycemia, presenting as permanent neonatal diabetes mellitus (PNDM). Conversely, only two cases of GCK homozygous mutations causing mild hyperglycemia have been so far described. We here report a novel GCK mutation (c.1116G>C, p.E372D), in a family with one homozygous member showing mild hyperglycemia.

Methods

GCK mutational screening was carried out by Sanger sequencing. Computational analyses to investigate pathogenicity and molecular dynamics (MD) were performed for GCK‐E372D and for previously described homozygous mutations associated with mild (n = 2) or severe (n = 1) hyperglycemia, used as references.

Results

Of four mildly hyperglycemic family‐members, three were heterozygous and one, diagnosed in the adulthood, was homozygous for GCK‐E372D. Two nondiabetic family members carried no mutations. Fasting glucose (p = 0.016) and HbA1c (p = 0.035) correlated with the number of mutated alleles (0–2).

In‐silico predicted pathogenicity was not correlated with the four mutations’ severity. At MD, GCK‐E372D conferred protein structure flexibility intermediate between mild and severe GCK mutations.

Conclusions

We present the third case of homozygous GCK mutations associated with mild hyperglycemia, rather than PNDM. Our in‐silico analyses support previous evidences suggesting that protein stability plays a role in determining clinical severity of GCK mutations.

Regulatory elements in the 5'region of 16SrRNA gene of Bacillus sp. strain SJ-101

Advancement in bioinformatics with the development of computational tools has enabled the in-silico prediction and identification of transcription regulatory factors and other genetic elements with great ease. In this study, computational analysis of sequence homology of 546 bp 5' region of 16SrRNA gene of Bacillus sp. strain SJ-101 resulted in identification of promoter-like sequences within the rrn gene. Using BPROM tool, the regulatory motifs like -35 and -10 boxes were mapped at 392 and 411 positions, respectively. Furthermore, the cis-acting elements as the binding sites for transcription factors (TF) cpxR and argR were identified at positions 413 and 416 at the upstream of an open reading frame (ORF). The probable functions of the putative TFs were predicted through the Uni-Prot/Swiss-Prot protein database. Search for the Shine-Dalgarno sequence (SD) found the presence of highly conserved SD sequence (AATACC), and a short 42 bp coding sequence/ORF bounded with characteristic transcription start site (AAC) and a stop codon (TGA) at positions 426 and 465 downstream to the promoter elements. A 13 amino acid long translation product of a short ORF has exhibited 100% homology with protein sequences of Bacillus spp., while showing some degree of polymorphism with other reference strains. The comparative homology of the small protein exhibited maximum similarity with Prolyl-4 hydroxylase of Chlamydomonas reinhardtii with 4.11 ZSCORE. The highly conserved regulatory elements and the putative ORF predicted within the 16SrRNA gene may help understand the role of relatively unexplored short ORFs within rrn operon, and their functional products in genetic regulatory mechanisms in eubacteria.