Sunday, August 25, 2019
Human phosphorylation isn't limited to just S/T/Y!!!
Okay -- my screenshot of Supplemental 12 looks pretty bad. That's my fault for using a PDF supplemental and using the Snipping tool.
What you can hardly see there is E-phospho with 100% sequence coverage. From a human cancer cell line. I picked this one out of the supplemental images because it is my favorite. I think that almost all of the Tyrosine-GalNaC peptides ever reported in humans are just S-GlcNaCs and I'm paranoid now. If a PTM is somewhere it doesn't belong, I'm more comfortable if there aren't traditionally expected amino acids floating around.
I've been through this brand new paper with some skepticism and thoroughness (at least what I have that passes for it) and: 1) I have a headache 2) I...geez....the evidence looks good to me that the authors are right -- we've only been seeing S/T/Y phospho because our enrichment methods only work "well" for those.... (the headache is because not every piece of software I use is easy to add a new chemical modification to an amino acid it shouldn't be on....and I'm never pumped to learn a new way to enrich phosphopeptides.)
What paper?? Sorry...this one!
Non-canonical? Oh yeah.
These authors demonstrate with Strong Anion Exchange (SAX) enrichment and a dizzying number of spectra (with comparisons to synthetic spectra in many cases) evidence that S/T/Y is just the beginning....
How's your head doing?
Wait. Do you see the super positive thing in the figure above? LOOK AT HOW MANY Y-phospho sites!!! This isn't an insanely frustrating and low recovery antibody based technique that no one has improved noticeably on since FACE was first described like 10 years ago. (I mean, it's great, but I've always hoped it would be improved upon somehow, but rabbit blood is...well...rabbit blood.... antibodies aren't just going to magically get more reliable....) THIS is a chemical enrichment that yields Y+phospho! Any reason to let the rabbits keep their blood is good for everyone (particularly reproducibility, and rabbits, of course!)
I need to type this again. SAX enrichment can get you Tyrosine Phosphopeptides!
I'm not going further into it. The paper is open access and you should check it out.
Are you skeptical enough that you'd like to start a RAW file download before you start reading? They're all available here.
You probably want to add some new chemical modifications to your search engine first....