Big shoutout to the recently official Dr. Eric Mosher for sending this over to me this morning!
Phosphopeptide standards are:
2) Hard to freaking find
3) Something with a finite expiration date.
Might get this part wrong.
What they did was design some big ol' E coli plasmids (?) that, once inserted into this unfortunate little organism, forces it to produce human phosphopeptides on 6xHisTags!
Check this out, though, this is where it is weird. This system, called pSERots or something, actually forces the insertion of phosphorylated serine as an amino acid. You don't have to put in a serine then phosphorylate it. It comes inserted in the protein. Now you know EXACTLY where that phosphorylation site is.
Need more phospopeptide standards? Grow more of that Ecoli. Extract the proteins and digest them -- phosphopeptides.
Rough cost estimates are that the process will generate around 600 micrograms of human phosphoserine standards for about $175 when they submitted the paper in February. Given inflation in the US caused entirely by the fact we don't tax the rich or control, in any way, the profits corporations are allowed to make, that is now $430. But either $0.02 per phosphopeptide or $0.05 per phosphopeptide is sure a lot less expensive than absolutely anything else!
There are other gems in this paper, like a new AScorePro algorithm for HCD and a cool website for helping to localize phosphosites!