Dear Hong !
First of all, assessing protein-protein interactions via MALDI is quite
difficult, since the chemical environment (matrix excess, low pH,
crystallisatio etc.) is everything but "physiological". Here a just a few
clues how to quickly evaluate the significance of the observation of the
2MH+ :
At which concentration or absloute amount of protein on the target do you
observe this ? Applying a lot of sample, protein dimers are quite
frequently seen rather as a result of sample concentration than of specific
interaction.
You can test this further by preparing a dilution series of your protein on
target and by monitoring the abundance of the dimer signal (5% rel.
abundance of your dimer signal probably already indicates, that you are at
the lower limit of observing it). This dilution exp. can be compared with
the same series of a protein of about the same size, that surely does not
form homodimers. This will rule out the pure concentration effect.
However, given the fact, that your protein is known for dimer formation and
regarding the size of the monomer of 90 kDa, I consider it likely, that you
are looking at some "real" protein interaction.
In order to further investigate this, you should consult the
"1st-shot-MALDI-experiments" of the Hillenkamp group (Neubauer, Hillenkamp
et al.) and definitely recrute ES-MS, which the first choice for direct
assessment of specific interactions, since it is the softer ionisation mode
(see van Dorsselaer et al.).
Hope this helps a bit.
Good luck and best regards,
Martin.
*****************************
Martin Kussmann, PhD
R&D, Protein Analysis /
Mass Spectrometry
CERBIOS-PHARMA S.A.
Via Pian Scairolo 6
CH - 6917 Barbengo (Lugano)
Switzerland
Phone: ++41 - 91 - 985 63 11
Fax: ++41 - 91 - 985 63 25
E-mail: rdbio2@cerbios.ch
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