Crystal structure of phosphoramide-phosphorylated thymidylate synthase reveals pSer127, reflecting probably pHis to pSer phosphotransfer

• 31P NMR found thymidylate synthase phosphorylated only on histidine residue(s).
• Crystal structure of the enzyme-dUMP complex showed a single phosphoserine (Ser127).
• Intermolecular pHis-Ser phosphotransfer under crystallization conditions is suggested.

Crystal structure is presented of the binary complex between potassium phosphoramidate-phosphorylated recombinant C. elegans thymidylate synthase and dUMP. On each monomer a single phosphoserine residue (Ser127) was identified, instead of expected phosphohistidine. As 31P NMR studies of both the phosphorylated protein and of potassium phosphoramidate potential to phosphorylate different amino acids point to histidine as the only possible site of the modification, thermodynamically favored intermolecular phosphotransfer from histidine to serine is suggested.

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