You are right, MALDI-TOF give a molecular mass of 14,463 kDa (close to the predicted molecular mass predicted from AA sequence)

It was discussed in multiple article that the mobility of alpha synuclein in PAGE provide an apparent mass of ~19 kDa which may reflect a low binding of the unfolded and acidic C-terminal fragment to SDS. (Surguchov 2008) PMID: 19081538

I am wondering how you are purifying your protein, maybe it may be explain by a  particular folding? Did you compared your results with cell or tissue lysate?

Check your sds concentration and add fresh beta-mercaptoethanol. 

Profusely mixing and boiling your sample is advised to ensure denaturalization. 

Thanks  Sergio 

I will do the advice.

You are right, MALDI-TOF give a molecular mass of 14,463 kDa (close to the predicted molecular mass predicted from AA sequence)

It was discussed in multiple article that the mobility of alpha synuclein in PAGE provide an apparent mass of ~19 kDa which may reflect a low binding of the unfolded and acidic C-terminal fragment to SDS. (Surguchov 2008) PMID: 19081538

I am wondering how you are purifying your protein, maybe it may be explain by a  particular folding? Did you compared your results with cell or tissue lysate?

Dear Nicolas

Thank you for your comment. In fact, we did not compare our results with cell or tissue lysate. However, the protein goes under fibrillation process well and the fibrillar forms of protein cause cell death significantly. CD spectrum, AFM, ThT intensity and fluorescent microscopy confirmed the fibrillation of the protein. As far as I am concerned there were a report (I think from Harvard University) that they protein also appears on approximately 15 KD, however; other articles, showed that their protein appears on approximately 17 or 19 KD. I was wondering what is the reason?