Phosphohistidine phosphatase 1 (PHPT1) also dephosphorylates phospholysine of chemically phosphorylated histone H1 and polylysine - PubMed (original) (raw)

Phosphohistidine phosphatase 1 (PHPT1) also dephosphorylates phospholysine of chemically phosphorylated histone H1 and polylysine

Pia Ek et al. Ups J Med Sci. 2015 Mar.

Abstract

Background: Phosphohistidine phosphatase 1 (PHPT1), also named protein histidine phosphatase (PHP), is a eukaryotic enzyme dephosphorylating proteins and peptides that are phosphorylated on a histidine residue. A preliminary finding that histone H1, which lacks histidine, was phosphorylated by phosphoramidate and dephosphorylated by PHPT1 prompted the present investigation.

Methods: Histone H1 and polylysine were phosphorylated at a low concentration (3.9 mM) of phosphoramidate. Their dephosphorylation by recombinant human PHPT1 was investigated by using a DEAE-Sepharose spin column technique earlier developed by us for studies on basic phosphoproteins and phosphopeptides. Determination of protein-bound, acid-labile phosphate was performed by a malachite green method. Mass spectrometry (MS) was used to investigate the occurrence of N-ε-phospholysine residues in a phosphorylated histone H1.2 preparation, and to measure the activity of PHPT1 against free N-ω-phosphoarginine.

Results: Histone H1.2, which lacks histidine, was phosphorylated by phosphoramidate on several lysine residues, as shown by MS. PHPT1 was shown to dephosphorylate phosphohistone H1 at a rate similar to that previously described for the dephosphorylation of phosphohistidine-containing peptides. In addition, phosphopolylysine was an equally good substrate for PHPT1. However, no dephosphorylation of free phosphoarginine by PHPT1 could be detected.

Conclusion: The finding that PHPT1 can dephosphorylate phospholysine in chemically phosphorylated histone H1 and polylysine demonstrates a broader specificity for this enzyme than known so far.

Keywords: Histone H1; PHP; PHPT1; phosphohistidine phosphatase; phospholysine; phospholysine phosphatase; protein histidine phosphatase.

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Figures

Figure 1.

Figure 1.

Decrease in phosphate in phosphoramidate phosphorylated histone H1 (▪) and 30 kDa polylysine (⧫) during incubation with PHPT1. The concentration was 1 mg/mL of phosphohistone and 2 mg/mL of phosphopolylysine. An amount of 5 pmol PHPT1 was added per 51 µL incubation volume. The reaction was performed at pH 7.5 and 30°C during indicated times and was interrupted by centrifugation of 50 µL of the reaction mixture through a spin column containing 200 µL of DEAE-Sepharose equilibrated in 25 mM Tris/HCl pH 8.5. The protein-bound, acid-labile phosphate in the final eluate was analyzed as described under Methods. Each time point was analyzed in duplicate.

Figure 2.

Figure 2.

Amino acid sequence and phosphorylated sites of bovine histone H1.2 as determined by mass spectrometry. Lysine residues are marked red, and those identified as targets for the phosphorylation by phosphoramidate (i.e. seven residues) are highlighted. Out of the 305 peptides that were used to identify the protein, 14 peptides were reported to contain phospholysine.

Figure 3.

Figure 3.

MS/MS spectrum showing the fragmentation pattern of one of the peptides obtained after trypsin treatment of histone H1 from SignalChem. The y-ion series is shown in red, and the b-ions series is in blue. Also shown is y- and b-ions fitting with the loss of 18 Da in violet and turquoise, respectively. Other observed but unspecified mached ions are grey. The small inset at the top shows only the y- and b-ions, with the length of the staples representing the intensity of the ions.

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