Development of stable phosphohistidine analogues

Abstract

Protein phosphorylation is one of the most common and extensively studied posttranslational modifications (PTMs). Compared to the O-phosphorylation of Ser, Thr, and Tyr residues, our understanding of histidine phosphorylation is relatively limited, particularly in higher eukaryotes, due to technical difficulties stemming from the intrinsic instability and isomerism of phosphohistidine (pHis). We report the design and synthesis of stable and nonisomerizable pHis analogues. These pHis analogues were successfully utilized in solid-phase peptide synthesis and semi-synthesis of histone H4. Significantly, the first antibody that specifically recognizes pHis was obtained using the synthetic peptide as the immunogen.

Figure 1

(a) Structures of 3- and 1-pHis. (b) Design of pHis analogues. Nitrogen atoms in red (H-bond acceptors) are conserved in the pHis analogues. Hydrolytically labile N—P bonds (red) in pHis are replaced with stable C—P bonds (blue). Both analogues can be prepared from the same building blocks by using different catalysts.

Figure 2

(a) Peptide dot blot using Ab-3pHis. The indicated peptides were labeled with 5-iodoacetamidofluorescein and spotted on a PVDF membrane (50 pmol each). To check for equal loading, the fluorescence of the same membrane was recorded at 520 nm upon excitation at 490 nm. (b) Western blots of recombinant histone H4 and mutants using Ab-3pHis. For the loading control, the initial blot with Ab-3pHis was stripped and reprobed with an α-H4 antibody.

Figure 3

Semi-synthesis of full-length histone H4 containing the 3-pHis analogue. Inset: Western blot showing that Ab-3pHis recognizes pTza-containing H4 protein 21 but not unmodified H4 control.

Scheme 1

Synthesis of Protected pTza Isomers

Scheme 2

SPPS of Histone H4 Tail Peptides with the pHis Analogues^a