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Comparison of posttranslational modifications of a protein |
Download MALDI-TOF
Service Information
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The primary
structure of the protein must be known!
Samples containing a given protein either obtained after expression in
different expression systems (e.g. prokaryotic vs. eukaryotic), or
before and after induction, or before and after in vitro modification
(e.g. phosphorylation) might be compared.
You provide
us with a) or b):
a)
Homogenous protein per sample, obtained by excision of bands from a
dried SDS-gel (stained with Coomassie Blue or Silver, preferably
without fixation). Please enclose a gel photo. Please, mention the
%age of the gel, clearly mark the bands which were excised from the
gel, and specify the molecular weight marker and the estimated
molecular weight of the proteins of interest.
b) At
least 25 µg of each purified native protein sample(ammonium sulfate
precipitate or lyophilized protein). Please, enclose a photo of an
analytical SDS-PAGE, mention the %age of the gel, clearly mark the
bands which correspond to the purified proteins, and specify the
molecular weight marker and the estimated molecular weight of the
proteins of interest. Recommend a suitable buffer for dialyzing
(ammonium sulfate precipitate) or dissolving (lyophilized material)
the proteins. If this is not a standard buffer, add your buffer in
sufficient amount (esp. for dialysis). Mention special requirements
of your protein with respect to solubility and stability (especially
important for membrane proteins).
Required
Information:
Protein identity
(incl. database entry number) and source of the protein samples
(organism, tissue, cell fraction etc.), and assumption which protein
modification is anticipated.
Please ship the
protein without cooling (dried gel bands, lyophilized protein) or on
blue ice (ammonium sulfate precipitate) to:
Gentaur
Avenue de l'Armée 68/B4
B-1040 Brussels BELGIUM
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Our service:
- (In gel)
trypsination of the protein (bands) of interest (Protein is cleaved
at arg and lys sites into peptides)
- MALDI-TOF Mass
Spectometry analysis of the tryptic peptides
- Peptides
carrying posttranslational modifications are identified by comparing
their actual mass with their theoretical mass peak by peak. This
process is carried out by trained scientists. A list of experimental
peptides that correspond to unmodified peptides is generated, then a
list of experimental peptides that match to peptides which carry
modifications of cystein residues, methionine residues, or other
modification as documented in SWISS-PROT is created. In order to
find novel modifications, the mass differences between all
experimental peptides and all theoretical peptides are calculated.
If a mass difference corresponds to the mass of any known
modification the peptide is classified as potentially modified.
Within the peptide the potential amino acid(s) that may carry the
modification in question is/are suggested.
- A comparison
list of modifications for the different protein samples is
delivered.
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Order
Information:
Cat. Nr.
CPPM01: Comparison of Posttranslational Modifications of a
Protein by MALDI-TOF-MS, proteins shipped in protein gel bands
Price: 495 Euro per sample (minimum: 2 samples)
Cat. Nr.
CPPM02: Comparison of Posttranslational Modifications of a
Purified Protein by MALDI-TOF-MS
Price: 720 Euro per sample (minimum: 2 samples)
Please note:
In case the protein amount or purity was not sufficient to perform
MALDI-TOF MS, a set up fee of € 175 is charged.
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Example: |
Acetylation
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HMFBPase
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HMFBPase
(S.cerevisiae)
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HMFBPase
(E.coli)
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Acetylation is the
binding of an acetyl group to an amino acid. This adds about 42 Da to
the acetylated peptide. If the acetylation affects the N-terminus of the
peptide, the first amino acid methionine can be eliminated. This causes
a loss of 131.1 Da corresponding to the mass of the methionine, but the
concomitant addition of the acetyl group reduces this mass loss to about
89 Da. In the example shown above the protein purified from E. coli is
not acetylated (as expected) and contains the first methionine.
Accordingly, the mass corresponding to the unmodified peptide fragment
T1-16 (m/z 1913.8) was detected. The peak corresponding to the T1-16
fragment was not measured in the digest of the same protein expressed in
either yeast or human skeletal muscle. Instead, the peak corresponding
to the loss of methionine and the addition of an acetyl group (on the
threonine 2) was detected (m/z 1825.2).
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Last modified:
05/19/16
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