Enhanced Diagnostic Tools
Bio-Synthesis protein sequencing services deliver accurate and reliable protein characterization and identification.
While mass spectrometry of peptides by enzymatic digest is a common method of protein identification, Edman sequencing (N-Terminal sequencing), also
known as automated Gas Phase Sequencing (GPS), provides additional data which is unavailable via mass
spectrometry methods. GPS is used to identify unknown proteins as well as to check the quality of recombinant proteins and determine enzyme cleavage
sites. It is a powerful complimentary technique used throughout all stages of drug
Edman sequencing offers two services for protein characterization
With our service you receive,
Please Contact Us or send an email to firstname.lastname@example.org to discuss your specific project
in more detail. We will provide you with a full proposal within two days, including analysis protocols, time lines and costs.
Quality control is provided
by utilizing appropriate internal and external standards as recommended by instrument
manufacturers. All analysis utilize the latest analytical
Our N-terminal protein sequencing uses automated Edman chemistry, carried
out on an Applied Biosystems protein sequencer and equipped with an on-line HPLC
system. This breaks down a protein/peptide sequentially into its constituent amino
acids from the N-terminus of the sample. The amino acid produced is derivatized
and separated by RP-HPLC and is visualized by UV detection for each cycle of Edman
chemistry. The amino acids are quantified by comparison to a standard mixture. If
C-terminal sequencing is required, a mass mapping by MS/MS for research will be
conducted for a full characterization of their recombinant protein.
Upon request, we first carry out Edman sequencing and report the first 7 amino acids
in the N-terminus of a protein, but some proteins contain signal sequences that
may not be correctly processed. Other proteins are truncated as part of the degradation
process. While some proteins are N-terminal modified by acetylation, pyroglutamic
acid and other blocking groups that will prevent successful N-terminal sequencing. There is not currently an established chemical sequencing method
for protein C-terminus.
Proper sample preparation is crucial for optimal protein sequencing results. One
important parameter is sample contamination with other proteins because it becomes
more difficult to produce useful data as the sequence of the 'target' may be obscured
by the presence of other sequences. Additional considerations such as concentration,
volume of sample, and the presence and concentration of detergents, glycerol, buffers
and other salts can also affect sequencing result. Prior to sending samples, investigators
are recommended to contact our facility to discuss the required analysis. This is
necessary to insure that the most efficient and cost-effective analytical methods
are employed. Samples are normally analyzed in the order of their receipt, but special
arrangements can be made for unstable samples. A sample submission form and guidelines
should accompany each set of samples. Consult with our technical
support for details.
Note: Please submit all samples in 1.5 ml polypropylene microcentrifuge
tubes for efficient handling. Thank you.
The sample will be reconstituted in 0.05% TFA/50% acetonitrile, 70% formic acid,
or 100% TFA for loading, unless specified otherwise. If there will be a solubility
problem, please contact us.
Buffers and primary amines: Tris buffer is commonly used for protein
purification. Tris and glycine are common in samples recovered from SDS-PAGE.
Glycerol and sucrose: These reagents are often added to buffers
designed for the storage and handling of proteins. These compounds are not volatile
and leave a highly viscous residue.
Nonionic detergents: Triton X-100, Brij, and Tween solutions often
contain aldehydes, oxidants and other contaminates that can inhibit Edman degradation
SDS: Large quantities of SDS can cause instrument malfunction and
may lead to the loss of sample from the filter.
CAUTION! Dialysis tubing is often a source of contaminants and other interfering
substances. Avoid dialysis as a last step in sample preparation or use thoroughly
cleaned, high-quality tubing. Always dialyzed against a salt counter ion or dilute
acid to prevent the protein and contaminates that may be present from sticking to
If you are unable to eliminate these materials from your buffers PLEASE DISCUSS
WITH THE BSI STAFF BEFORE YOU SUBMIT YOUR SAMPLES.
Samples purified by SDS-PAGE must be electroblotted onto PVDF membrane
and sequenced directly from PVDF membranes. Nitrocellulose membrane is NOT acceptable
as it is not resistant to the Edman chemistry. We have recommended protocols
for Electroblotting and staining available on our Electroblotting
page. In general we recommend
The average sequencing yield from PVDF is approximately 15% instead of the 50-80%
expected for solution samples, so a 10 pmols sample on PVDF usually gives 1.5 pmols
amino acid peaks. This is due to water vapor that aids PiTC coupling in the Edman
chemistry being repelled by the PVDF. Therefore, our preferred stains are old-fashioned
Coomassie blue and Ponceau S. or Amido black (silver stains may not be used)
Destained extensively with at least 4 changes of destaining solvent.
Washed with 3-4 changes of ultra-pure water to lower the very high concentrations
of Tris, glycine, and other gel and transfer buffers that otherwise will interfere
DO NOT remove all the stain from the bands, they need to be clearly visible for
excision as PVDF without protein hinders the flow of chemicals thru the instrument's
sample cartridge. This sample cartridges can hold approximately 20 square mm of
PVDF membrane. This is roughly equivalent to a slice 1-2 mm high and the width of
three lanes of a mini-gel. We prefer that a non-glycine electroblot buffer be
used. Glycine is an amino acid and will contaminate the sample resulting
in uninterpretable sequence information for one or two cycles. Please
contact us with any questions.
Protein can be passively eluted from polyacrylamide in an overnight procedure
for an additional fee.
Passive elution is generally less efficient than electroblotting and does not work
with high mw proteins. It is recommended for well stained protein bands that are
less than 60kDa.
Your sample will be loaded into the sequencer cartridge by spotting a pure protein
liquid sample onto a Biobrene-saturated glass fiber filter or by placing a small
amount of PVDF membrane directly into the sample cartridge. Liquid samples that
contain contaminating or compounding chemicals (see under Liquid Samples) will be
loaded onto ProSorb cartridges and washed with 0.2% TFA to remove contaminants before
sequencing commences. There is an additional charge for this preparation step.
All reagents and solvents must be of the highest purity available (HPLC grade, sequencing
grade and electrophoresis grade reagents) to avoid contaminating substances. Avoid
molecular biology grade reagents.
Always wear gloves and work in a clean dust free area. Dust and finger prints are
a major source of contaminating amino acids present in sequencing samples.
Avoid drying the sample in glass tubes. This can lead to substantial loss of sample
for some proteins. Sample volumes should be less than 150 ul, however with the advent
of ABI's Prosorb Sample Preparation Cartridge, sample volumes of up to 750 ul may
The sample should be in a volatile solvent or buffer such as acetic acid, formic
acid, trifluoroacetic acid, triethylamine, pyridine, acetonitrile, propanol, water,
or ammonium bicarbonate (if lyophilized repeatedly).
A minimum of 10 to 50 pmol of sample should be analyzed. Our Precise sequencer can
sequence 1-2 pmol of sample at its highest level of sensitivity. However, it is
more practical to sequence larger amounts of protein to be confident of the sequence
obtained or to be confident that the N-terminus is blocked if no sequence is obtained.
In most cases the amount of sequence able material is underestimated by sample loss,
inaccurate quantitation, or N-terminal blockage during sample preparation. Therefore,
be sure to err on the side of too much sample rather than too little!
The sample may contain a small amount of detergent (less than 0.1% SDS). Larger
amounts can cause instrument problems.
When submitting electroblotted samples on PVDF for sequencing, always try to have
as much protein as you can in as small an area of PVDF as possible. Too much PVDF
in the sequencer's reaction cartridge can lead to excessive sequencer background.
One reason why the initial yields are often unexpectedly low, is that the amount
of sample present is overestimated by the investigator. The most reliable quantitation
method is from amino acid analysis. Lowry, BCA, dye binding assays and absorbance
are less accurate methods especially in the low microgram amounts.
We recommend that you send liquid samples in screw cap (with gasket) Eppendorf tubes
packed in such a way that are cushioned from the effects of FedEx. If a gasket-equipped
tube is not available, use Parafilm to assure that the cap does not pop off in shipping.
Keeping the sample cool is at the discretion of the investigator. We can receive
packages with wet ice or dry ice but all samples can only be received during normal
Samples for sequencing that are on PVDF membranes do not require being kept cool.
We recommend sending dried membranes between two pieces of clean filter paper by
FedEx Letter. We discourage you from sending individual slices of PVDF membrane.
Also, please include a print (or sketch) of the membrane indicating which band(s)
Protein Peptide Sequencing Submission