Purification and characterization of a class II α-Mannosidase from Moringa oleifera seed kernels

Momordica charantia seed proteins - Purification, biochemical characterization of a class II α-mannosidase isoenzyme and its interaction with the lectin and protein body membrane

Momordica charantia seeds contain a galactose specific lectin and mixture of glycosidases. These bind to lectin-affigel at pH 5.0 and are all eluted at pH 8.0. From the mixture, α-mannosidase was separated by gel filtration (purified enzyme Mr ∼ 238 kDa). In native PAGE (silver staining) it showed three bands that stained with methylumbelliferyl substrate (possible isoforms). Ion exchange chromatography separated two isoforms in 0.5 M eluates and one isoform in 1.0 M eluate. In SDS-PAGE it dissociated to Mr ∼70 and 45 kDa subunits, showing antigenic similarity to jack bean enzyme. MALDI analysis confirmed the 70 kDa band to be α-mannosidase with sequence identity to the genomic sequence of Momordica charantia enzyme (score 83, 29 % sequence coverage). The pH, temperature optima were 5.0 and 60o C respectively. Kinetic parameters KM and Vmax estimated with p-nitrophenyl α-mannopyranoside were 0.85 mM and 12.1 U/mg respectively. Swainsonine inhibits the enzyme activity (IC50 value was 50 nM). Secondary structural analysis at far UV (190-300 nm) showed 11.6 % α-helix and 36.5 % β-sheets. 2.197 mg of the enzyme was found to interact with 3.75 mg of protein body membrane at pH 5.0 and not at pH 8.0 suggesting a pH dependent interaction.

Biomarker identification of isolated compartments of the cell wall, cytoplasm and vacuole from the internodal cell of characean Nitellopsis obtusa

Cells of characean algae are attractive for plant cell physiologists because of their large size and their close relation to higher plant cells. The objective of our study was to evaluate the purity of the compartments (cell wall, cytoplasm with plastids, mitochondria, nuclei and endomembrane system, and vacuole) separated mechanically from the internodal cells of Nitellopsis obtusa using enzymatic markers. These included α-mannosidase and malate dehydrogenase, vacuolar and cytoplasmic enzymes, respectively. The biomarkers applied revealed the degree of compartment contamination with the material from unwanted cell parts. The cell wall was contaminated slightly by vacuole and cytoplasm residuals, respectively by 12.3 and 1.96% of corresponding biomarker activities. Relatively high activity of vacuolar marker in the cell wall could be associated with the cell vacuoles in the multicellular structure of the nodes. The biomarkers confirmed highly purified vacuolar (99.5%) and cytoplasmic (86.7%) compartments. Purity estimation of the cell fractions enabled reevaluating nCuO related Cu concentrations in the compartments of charophyte cell. The internalisation of CuO nanoparticles in N. obtusa cell occurred already after 0.5h. In general, the approach seems to be useful for assessing the accumulation and distribution of various xenobiotics and/or metabolites within plant cell. All this justifies N.obtusa internodal cells as a model organism for modern studies in cell biology and nanotoxicology.

Purification, biochemical and biophysical characterization of an acidic α-galactosidase from the seeds of Annona squamosa (custard apple)

Alpha galactosidase is an exoglycosidase that cleaves α-D-galactose and has numerous applications in medicine, biotechnology, food and pharma industries. In this study, a low molecular weight acidic α-galactosidase was identified from the seeds of custard apple. The purification of α-galactosidase from the crude extract of defatted seeds was achieved by employing ammonium sulphate fractionation, hydrophobic interaction and gel filtration chromatographic techniques. The purified custard apple α-galactosidase (CaG) migrated as a single band in native PAGE corresponding to molecular weight of ~67 kDa and cleaved chromogenic, fluorogenic and natural substrates. CaG was found to be a heterodimer with subunit masses of 40 and 30 kDa. The kinetic parameters such as K_M and Vmax were found to be 0.67 mM and 1.5 U/mg respectively with p-nitrophenyl α-D-galactopyranoside. Galactose, methyl α-D-galactopyranoside and D-galacturonic acid inhibited CaG activity in mixed mode. The CD spectral analysis at far UV region showed that purified CaG exists predominantly as helix (35%), beta sheets (16.3%) and random coils (32.3%) in its secondary structure. These biochemical and biophysical properties of CaG provide leads to understand its primary sequence and glycan structures which will eventually define its novel physiological roles in plants and potential industrial applications.

Purification, biochemical/biophysical characterization and chitooligosaccharide binding to BGL24, a new PP2-type phloem exudate lectin from bottle gourd (Lagenaria siceraria)

Phloem Protein 2 (PP2), highly abundant in the sieve elements of plants, plays a significant role in wound sealing and anti-pathogenic responses. In this study, we report the purification and characterization of a new PP2-type lectin, BGL24 from the phloem exudate of bottle gourd (Lagenaria siceraria). BGL24 is a homodimer with a subunit mass of ~24 kDa and exhibits high specificity for chitooligosaccharides. The isoelectric point of BGL24 was estimated from zeta potential measurements as 5.95. Partial amino acid sequence obtained by mass spectrometric studies indicated that BGL24 exhibits extensive homology with other PP2-type phloem exudate lectins. CD spectroscopic measurements revealed that the lectin contains predominantly β-sheets, with low α-helical content. CD spectroscopic and DSC studies showed that BGL24 exhibits high thermal stability with an unfolding temperature of ~82 °C, and that its secondary structure is essentially unaltered between pH 3.0 and 8.0. Fluorescence titrations employing 4-methylumbelliferyl-β-D-N,N',N″-triacetylchitotrioside as an indicator ligand revealed that the association constants for BGL24-chitooligosaccharide interaction increase considerably when the ligand size is increased from chitotriose to chitotetraose, whereas only marginal increase was observed for chitopentaose and chitohexaose. BGL24 exhibited moderate cytotoxicity against MDA-MB-231 breast cancer cells, whereas its effect on normal splenocytes was marginal.

Mass spectrometry combined with affinity probes for the identification of CP4 EPSPS in genetically modified soybeans

Sample preparation methods used for genetically modified organisms (GMOs) analysis are often time consuming, require extensive manual manipulation, and result in limited amounts of purified protein, which may complicate the detection of low-abundance GM protein. A robust sample pretreatment method prior to mass spectrometry (MS) detection of the transgenic protein (5-enolpyruvylshikimate-3-phosphate synthase [CP4 EPSPS]) present in Roundup Ready soya is investigated. Liquid chromatography-multiple reaction monitoring tandem MS (nano LC-MS/MS-MRM) was used for the detection and quantification of CP4 EPSPS. Gold nanoparticles (AuNPs) and concanavalin A (Con A)-immobilized Sepharose 4B were used as selective probes for the separation of the major storage proteins in soybeans. AuNPs that enable the capture of cysteine-containing proteins were used to reduce the complexity of the crude extract of GM soya. Con A-sepharose was used for the affinity capture of β-conglycinin and other glycoproteins of soya prior to enzymatic digestion. The methods enabled the detection of unique peptides of CP4 EPSPS at a level as low as 0.5% of GM soya in MRM mode. Stable-isotope dimethyl labeling was further applied to the quantification of GM soya. Both probes exhibited high selectivity and efficiency for the affinity capture of storage proteins, leading to the quantitative detection at 0.5% GM soya, which is a level below the current European Union's threshold for food labeling. The square correlation coefficients were greater than 0.99. The approach for sample preparation is very simple without the need for time-consuming protein prefractionation or separation procedures and thus presents a significant improvement over existing methods for the analysis of the GM soya protein.

Moringa oleifera (drumstick tree) seed coagulant protein (MoCP) binds cadmium - preparation and characterization of nanoparticles

Moringa oleifera is grown globally. It is a multipurpose tree and the seeds are rich in phytochemicals with antimicrobial activities. The crude powder of seeds clarify the turbid and metal contaminated water. M. oleifera (drumstick tree) seed coagulant protein (MoCP) was isolated to homogeneity from the crude extracts by carboxymethyl cellulose chromatography (CMC) and gel filtration. The molecular weight of the protein on gel filtration was 13 kDa and in SDS-PAGE it migrated as a single band under reducing conditions with molecular mass of 6.5 kDa (dimeric). Immobilized MoCP selectively binds cadmium from aqueous solutions (pH 2.0-7.0) with maximum binding at pH 6.0 in 180 min when tested at 10-600 minutes. It also bound the metal in the concentration range of 30-70mgL-1. The adsorption kinetics was better described by pseudo second order and the data better explained by freundlich isotherm model than Langmuir isotherm model as in Freundlich model the correlation coefficient (R2) is high and the calculated qmax is very close to the experimental qmax rather than Langmuir isotherm model. Furthermore, the nanoparticles of MoCP were prepared and characterized using transmission electron microscopy (TEM). The authenticity of the isolated protein and the nanopraticles prepared was confirmed by specific reactivity with the MoCP antibody raised earlier in our laboratory.

Sequential processing of mannose-containing glycans by two α-mannosidases from Solitalea canadensis

Two putative α-mannosidase genes isolated from the rather unexplored soil bacterium Solitalea canadensis were cloned and biochemically characterised. Both recombinant enzymes were highly selective in releasing α-linked mannose but no other sugars. The α-mannosidases were designated Sca2/3Man2693 and Sca6Man4191, and showed the following biochemical properties: the temperature optimum for both enzymes was 37 °C, and their pH optima lay at 5.0 and 5.5, respectively. The activity of Sca2/3Man2693 was found to be dependent on Ca(2+) ions, whereas Cu(2+) and Zn(2+) ions almost completely inhibited both α-mannosidases. Specificity screens with various substrates revealed that Sca2/3Man2693 could release both α1-2- and α1-3-linked mannose, whereas Sca6Man4191 only released α1-6-linked mannose. The combined enzymatic action of both recombinant α-mannosidases allowed the sequential degradation of high-mannose-type N-glycans. The facile expression and purification procedures in combination with strict substrate specificities make α-mannosidases from S. canadensis promising candidates for bioanalytical applications.