Sulfate or Phosphate?

Some months before @robField’s tweet setting off the train that led to the Eu sensor that discriminates PAP/PAPS, Ed Yates and myself were having a curry with Dulce Papy-Garcia from UPEC, who had examined one of our PhD students. A matter we discussed at length was ‘why sulfate’. That is, why does biology use both sulfate and phosphate to modify post synthesis proteins, polysaccharides and other molecules. We didn’t come up with an answer,  but the conversation led Ed and myself to consider that the question merited exploration. 

This we thought would be a simple matter. 

It turned out to be one of the most difficult papers Ed and myself have written, to the extent that after N drafts (where N is a significantly larger number than either of us had experienced in any previous writing exercise) and too many summers we still had nothing satisfactory. So, we cunningly inveigled two colleagues, Tim Rudd from NIBSC and Marcelo Lima from Keele to join us on what we advertised as the sunny beach of sulfate and phosphate, but which in reality was a rather dank quagmire. There is though something about strength in numbers, and with very helpful input from Steve Butler in Loughborough, we arrived at what we considered a satisfactory synthesis. Happily, the reviewers concurred, and the paper is now published at Royal Society Interfaces, “Phosphorylation and sulfation share a common biosynthetic pathway, but extend biochemical and evolutionary diversity of biological macromolecules in distinct ways”.

This is by no means the last word on the matter, but along with some previous thoughtful papers we cite (if we have missed one, please let me know) it provides some ideas that may help us to understand why biology co-opted particular elements from the inorganic world to perform groups of functions vital to life as we know it now.

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Real-time sulfotransferase assay

More sulfation

Earlier this year Simon Wheeler (who now has a well deserved substantive position, congratulations!) and Steve Butler published the first output from the BBSRC TDRI awarded to Steve, with myself and Ed Yates in supporting roles. It is always nice to collaborate with real chemists, as it reminds me I am very much a pseudo chemist, and I learn a lot. After what I would consider a quite heroic effort on the synthesis front, Simon and Steve pulled out a very useful sensor, based on a europium complex. The Eu sensor has good selectivity for PAP over PAPS, the universal sulfate donor. The assay works well and is very amenable to high throughput 384 well format assays (= more papers on the way). So we can now measure sulfotransferase activity in realt-ime independently of the acceptor for pretty much any enzyme-substrate combination. This represents an important tool for the wider sulfotransferase community. 

The paper also demonstrates the importance of social media in science, as a means to access in a non-direct manner new information that sets off an innovative project. I saw tweet from @Fieldlab highlighting a paper from Steve’s lab on lanthanide sensors able to discriminate nucleotide phosphates and read the paper. Naively I thought PAP/PAPS sensing using such compounds should be easy, so I contacted Steve. After some preliminary tests with PAP and PAPS on his side, we wrote the grant – another lesson here, as the application neared final from I went over to Loughborough for a meeting, which allowed us to iron out a few problems far more effectively than by electronic communication. The work was, as hinted above, far from straightforward, but like everything that is new, very rewarding and continues to be so.

I have just moved from the bird site to the proboscidean one and things look like there will be even more of such ‘random access’ of information there, so let’s see what turns up!

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