The human androgen receptor is a heavily studied protein but I couldn't find an explanation about why it is always characterized as 110 kDa, when Uniprot (http://www.uniprot.org/uniprot/P10275) predicts the full length isoform to be 99 kDa?
The migration of the androgen receptor during SDS polyacrylamide gel electrophoresis corresponds to the mass of a 110 kDa protein, larger than the mass indicated in UniProtKB/Swiss-Prot (http://www.uniprot.org/uniprot/P10275).
This is due to the fact that the mass in UniProt corresponds to the mass of the protein without any protein modifications.
Please note that the migration of a protein during SDS polyacrylamide electrophoresis (SDS PAGE) depends on many factors. It is determined not only by protein mass, but also by its charge, its hydrodynamic properties and by post-translational modifications, such as N-glycosylation and phosphorylation.
The human androgen receptor is phosphorylated (see for exapmple PubMed=2302201), and that certainly contributes to the difference between the apparent mass (determined by SDS PAGE) and the real mass of the unmodified protein.
Please don't hesitate to contact the UniProt helpdesk ([email protected]) for future questions.
It could very well be due to charge or hydrodynamic properties. It is synthesized as a 110 kDa protein (according to SDS-PAGE), which is rapidly phosphorylated, and treatment with alkaline phosphatase restores the 110 kDa band (PMID: 1955082). So, I don't think it is due to phosphorylation. Also, glycoyslated protein are secreted and the AR is an intracellular protein.
I was just wondering if anyone knew anything any more specific. It is a heavily studied steroid receptor, with important clinical uses.
It may depend at least partially on the length of the N-Terminal Polyglutamine tract which can vary a lot. Not sure which version of the receptor (with which length of tract) was used to calculate molecular weight on Uniprot. There are also other post-translational modifications other than phosphorylation and glycosylation. Acetylation is becoming more widely studied as well. Not sure it has been shown to be acetylated but I would not be surprised to find that it is.
Marc, Uniprot and Pubmed both use the same gene/mRNA/protein sequence (http://www.ncbi.nlm.nih.gov/gene/367). There would have to be an extra 100 glutamines to account for a 10 kDa difference.
Similarly, for acetylation: an acetyl group only masses about 43 daltons, so the AR would have to be acetylated more than 200 times to account for this mass difference. I don't think this is it, either.
It may just be a mystery of *waves hands* hydrodynamic properties, since no I have asked seems to know!
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