Source of Karnal bunt infected wheat grain
Karnal Bunt infected wheat grains were collected from (IIWBR) Indian Institute of Wheat and Barley Research, Karnal and Punjab Agriculture University (PAU), Ludhiana.
Collection of teliospores and extraction of teliosporic cell wall protein
Teliospores of T. indica were extracted from the contaminated wheat seeds using forceps, needle, surgical blades and brush. Seeds were incised using a needle to loosen the spore mass. Teliospores released by shaking the incised seeds were used as a source of immunogen. Teliospores were mechanically lysed by grinding in mortar pestle using in liquid nitrogen followed by adding 0.5% SDS as an extraction buffer to lyse the spores for obtaining solubilized protein. Crude lysate was centrifuged at 10,000 g for 15 min at 4 °C twice subsequently to remove particulate debris. Supernatant was centrifuged at 10,000 g for 10 min at 4 °C. and transferred to fresh Eppendorf. 2mM Phenyl Methyl Sulfonyl Fluoride (PMSF) was added to the supernatant solution and stored at -20°C for further use. Protein was estimated using bovine serum albumin (BSA) as standard according to Bradford method (Bradford 1976).
Preparative SDS PAGE
SDS-PAGE was performed to resolve proteins and polypeptides bands of range 14-90 kDa. The SDS (12%) was used to analyze solubilized teliospore’s protein. Preparative gel electrophoresis was carried out using mini-PROTEAN Tetra Cell, Bio-Red. 12% acrylamide gel was cast in the 1mm internal diameter gel to a height of 7 cm with a 2.5 cm 5% stacking gel. The gel was run at 100V at room temperature and once the tracker dye reached to bottom of resolving gel. Gel was fixed in Coomassie brilliant blue for 2-3 hours after electrophoresis Target 28kDa protein band was collected through preparative SDS-PAGE (Singh et al. 2013).
Two-Dimensional Gel Electrophoresis (2-DE)
Teliosporic wall 28kD protein band was eluted from preparative gels of crude protein by gel elution protocol using our lab made two different elution buffers A and B (Patent no. 345176). Eluted bands were incubated with 1000 µl of buffer A for 5 mins and rinsed with distilled water. Excised gel pieces were crushed with the help of mortar and pestle using buffer B on ice and incubated for 1 hr at 4°C. Mixture was then centrifugation at 12,000 g for 20 min at 4°C and supernatant was precipitated using triple volume of chilled TCA/Acetone (10% w/v) overnight. Precipitated protein was recovered by centrifugation at 10,000 g for 20 min at 4°C. Pellet was washed with chilled acetone and centrifuged at 10,000g for 10 min at 4°C. The residual acetone was removed by air drying. Precipitated protein was further dissolved in 25 µl of rehydration buffer (2%[w/v] CHAPS, 2M thiourea, 8M Urea, 50 mM DTT) and stored at -20 °C.
Protein Quantification:
Protein Concentration was estimated by Bradford’s dye binding method (Bradford 1976). Different Bovine Serum Albumin (BSA) concentration was used to plot the standard curve.
Two-dimensional gel electrophoresis (2–DE)
Protein sample (125 μg) was dissolved and rehydrated in 125 μL of IEF rehydration buffer with 0.01% [WV] bromophenol blue on to IPG strip of range 3-10; for 16 h for 2-Dimensional electrophoresis according to Bio-Rad protocol. Isoelectric focusing (IEF) was performed by using Bio-Rad Protean IEF Cell system following slight modification on Fragner et al 2009: 250 V for 1 hr, 1000 V for 1 hr, 5 h at 10,000 V, 250 V for 1 hr, followed by 4 hr gradient from 1000 to 10,000 V, focused on 20000 V hr at 10, 000 V. Maximum current was kept at 50 mA. Strip was then reduced and alkylated by using equilibration buffer I (6 M urea, 0.375 M Tris (pH 8.8), 10% SDS, 20% glycerol and 130 mM DDT) and equilibration buffer II (6 M urea, 0.375 M Tris (pH 8.8), 10% SDS, 20% glycerol and 130 mM Iodoacetamide), respectively. Second-Dimension electrophoresis was performed using Mini-PROTEAN Tetra Cell (Bio-Rad) with 12% acrylamide gel at 100V until the bromophenol blue dye reached the bottom of the gel. After electrophoresis, Coomassie Brilliant Blue (CBB) G-250 was used to stain the gel for 4-6 hours and dipped the gel in solution (10% methanol, 7% glacial acetic acid (v/v) to distain thoroughly. Image of the gel was taken by alphaimager gel documentation system (Protein simple, California, USA). Spots were excised for further identification using MALDI- TOF/TOF.
Tandem Mass Spectrometry and Database Searching
In order to obtain mass spectra, in-gel digestion of proteins was done by manual excision of teliospore proteins from two-dimensional gel stained with Commissive Brilliant Blue. These excised protein spots were suspended in 10% glacial acetic acid and then subsequently destained at 40°C using 50 mM NH4HCO3 in 50% (V/V) methanol for 1 hour. Vacuum centrifugation is used to completely dry out gel particles for peptide digestion with 5 ng/µl of trypsin for 16 hours at 37°C. 0.1 % trifluoroacetic acid (TFA) solution in 50 % acetonitrile was used to extract digested peptide fragments and then resuspending it in 5 mg/ml of α-cyano-4-hydroxycinnamic acid in 50 % acetonitrile containing 0.1 % TFA. Further digested peptides were subjected to tandem mass spectroscopy (ULTRAFLEX III TOF/ TOF, Bruker Daltonics). Tandem Mass Spectrometry (MS/MS) spectra were acquired with 2500 laser shots per fragmentation spectrum at 1600 laser shots per spectrum. MS/MS fragmentation spectra of precursor ions were obtained from strongest ten peaks from MS spectra. Spectra analysis and peak list file formation has been done by Flex analysis software 3.0 (Bruker Daltonics). MASCOT (http://www.matrixscience.com) search engine was used to search peak list files on NCBI (http://www.ncbi.nlm.nih.gov) nonredundant database version 79353501, 20160114 sequences and 28992349963 residues for “Fungi”. Search parameters were followed to proteolytic enzyme, trypsin; variable modifications, oxidation (M); taxonomy, Fungi; max missed cleavages, fixed modifications, carbamidomethyl (C); peptide mass tolerance, 500 ppm fragment mass tolerance and molecular weight at 2 Da. A protein is said to be confident in identification if protein score is more than 70 %.
In-silico approaches
Sequenced genome of T. indica (Kumar et al. 2017) was used for identification of candidate’s protein. Identified proteins from T. indica genome were used for further sequence and structure based functional annotation. Sequence of identified proteins were retrieved from NCBI conserved domain database (CDD) and BLAST tools to identify and select sequence showing homology with the proteins that have structural and functional similarity with identified candidate proteins. InterProScan was used with different protein recognition methods from the InterProScan consortium for identification of motifs. Motifs act as signature to define a protein in protein family, such as enzyme in which motifs are involved with catalytic function (Mitra et al. 2016).
Physicochemical Properties and Functional Characterization
Physicochemical properties including the number of amino acids, molecular weight aliphatic index (Ikai et al. 1980), instability index (Guruprasad et al. 1990) theoretical isoelectric point (pI), Grand average of hydropathy (GRAVY) (Kyte et al. 1982) of proteins were assessed by ExPASy Protparam tool (http://web.expasy.org/protparam/) (Gasteiger et al. 2005).
Structure Validation and Analysis
Three-dimensional structures of identified proteins were predicted using RaptorX (http://raptorx.uchicago.edu.) and visualization done by Chimera software (Pettersen et al. 2005). Ramachandran plot and protein stability analysis and validation of each protein model was done by various bioinformatics tools like RAMPAGE server (Lovell et al. 2002), DALI server (Holm et al. 2020) and ProQ server (Wallner et al. 2003). Modeled protein structures were visualized and analyzed by PyMol software (Seelinger and De Groot 2010).
Protein-Protein Docking
Protein-Protein docking was done using ClusPro server (Comeau et al. 2004a; Comeau et al. 2004b). PIPER, a docking program with Fast Fourier Transform (FFT) correlation approach was used to calculate the docked complex energy with protein interaction (De Virgilio et al. 1994). Much fewer near native structures are only retained, because of the more accurate pairwise interaction potential of PIPER. Algorithm clusters the structures by considering pairwise RMSD as the distance measure. All bioinformatics tools and database used for sequence and structure analysis are listed below in the Table1.
Table 1: List of Bioinformatics Tools and database used for sequence and structural based function annotation.
S.No.
|
Web server
|
Function
|
Web address
|
References
|
1.
|
NCBI
|
Retrieval of protein sequence
|
https://www.ncbi.nlm.nih.gov/
|
--
|
2.
|
BLAST
|
To find similarity between sequence in the database
|
https://blast.ncbi.nlm.nih.gov/Blast.cgi
|
Altschul et al. (1990)
|
3.
|
ProtParam Tool
|
To evaluate physio- chem properties
|
https://web.ex23pasy.org/protparam/
|
Gasteiger et al. (2005)
|
4.
|
Functional analysis tools
|
|
|
|
i)
|
Conserved domain database
|
To find conserved domain in the sequence
|
https://www.ncbi.nlm.nih.gov/Structure/cdd/cdd.shtml
|
Marchler- Bauer et al (2015)
|
ii)
|
Interproscan
|
To categorized by predicted domain and important sites
|
https://www.ebi.ac.uk/interpro/
|
Blum et al. (2020)
|
5.
|
Structural prediction
(RaptorX)
|
Protein structure and function prediction
|
http://raptorx.uchicago.edu/
|
Kallberg, (2012)
|
6.
|
Structural validation
|
|
|
|
i)
|
RAMPAGE
|
To evaluate the quality of Ramachandran plot
|
http://mordred.bioc.cam.ac.uk/~rapper/rampage.php
|
Lovell, et al.,
(2003)
|
ii)
|
Chimera software
|
Visualization of modeled structure
|
https://www.cgl.ucsf.edu/chimera/download.html
|
Pettersen et al. (2005)
|
iii)
|
ProQ server
|
Assessment of the protein
|
https://proq.bioinfo.se/ProQ/ProQ.html
|
Wallner and Elofsson (2003)
|
iv)
|
DALI server
|
Comparison of protein against protein database
|
http://ekhidna2.biocenter.helsinki.fi/dali/
|
Holm. (2020)
|
v)
|
Autodock
|
Protein-Protein interaction
|
http://vina.scripps.edu/
|
Trott and Olson. (2010)
|
vi)
|
PyMol
|
Visualization of docked protein
|
https://pymol.org/2/
|
Seelinger and De Groot. (2010)
|