Effect of PTMs and pI on migration in SDS-PAGE - (Jul/14/2006 )

Hi!

I have a protein with theoretical pI 6.73.
In a mutant variant of this protein 5 aa are changed and the theoretical pI changes to 8.27.
Wt and mutant have same protein size.

In 12.5% SDS-PAGE the mutant variant show altered migration pattern
- could that change in pI account for this (even if proteins are in SDS?)

Another posibility is posttranslational modification(s) of the mutant protein.
When looking at the aa sequence acetylation or methylation is most likely,
but these are small - would one or two such modifiactions affect migration in SDS-PAGE?

What about phosphorylation?

Thanks!

phosphorylation can modify slightly the migration of proteins.