swissprot enquiry - (Aug/25/2008 )

In the swissprot database, the molecular weight of the protein is given in terms of unprocessed precursor , for eg 20550 da, will it be the same mol.wt when we run the same protein in SDS PAGE gel ? Thanks in advance for the replies.

it is a theoretical value calculated form the primary sequence
experimental MW will necessarily depends on the post-translation modifications including glycosylation, protease processing... and even on the post-transcription level
finally, it will mostly depends on the system used for generating the molecule (insect, bacteria, mammalian cell)
then covalent addition of sugar or any other molecule to the protein will be observed during the SDS-PAGE i(n the case you do not treat your sample with glycosidase before elcetrophoresis)
I also think that there is not only one homogeneous population of protein, I mean your sample contains protein more or less modified in proportions we could not be able to determine, that is why you should observe smear-like profils in some cases...