First Structure of a Eukaryotic Phosphohistidine Phosphatase

Abstract

Phosphatases are a diverse group of enzymes that regulate numerous cellular processes. Much of what is known relates to the tyrosine, threonine, and serine phosphatases, whereas the histidine phosphatases have not been studied as much. The structure of phosphohistidine phosphatase (PHPT1), the first identified eukaryotic-protein histidine phosphatase, has been determined to a resolution of 1.9 Å using multiple-wavelength anomalous dispersion methods. This enzyme can dephosphorylate a variety of proteins (e.g. ATP-citrate lyase and the ␤-subunit of G proteins). A putative active site has been identified by its electrostatic character, ion binding, and conserved protein residues. Histidine 53 is proposed to play a major role in histidine dephosphorylation based on these observations and previous mutational studies. Models of peptide binding are discussed to suggest possible mechanisms for substrate recognition.Reversible phosphorylation of residues is crucial in a variety of signaling pathways. Most of our understanding regarding these signaling events in eukaryotes comes from tyrosine, serine/threonine kinases, and phosphatases (1). Less well characterized is histidine phosphorylation-dependent signaling in eukaryotes. A little more than thirty years ago, Histone H4, the first vertebrate protein with a phosphorylated histidine residue, was identified (2). Since then there has been a measured increase in knowledge of mammalian histidine kinases (3). Unfortunately, very little information regarding eukaryotic histidine phosphatases has been available during this same period. This nescience is interesting because histidine phosphorylation is quite prevalent in the cell and likely accounts for ϳ6% of all phosphorylation in eukaryotes (4). Thus far, only one protein (the ␤-subunit of heterotrimeric G proteins) in vertebrates has been identified as undergoing reversible histidine phosphorylation where both the kinase (NDPK B) and phosphatase (PHPT1) 2 are known (for a recent review, see Ref. 5). However, more information regarding histidine phosphatases is slowly beginning to emerge. To date, the only other structure of a histidine phosphatase is Escherichia coli SixA (6). Under certain anaerobic respiratory conditions, SixA is involved in down-regulation of the E. coli ArcB-to-ArcA phosphorelay system. SixA shows structural homology to the well studied family of arginine-histidine-glycine (RHG) phosphatases (6) but no sequence homology to PHPT1.Mammalian phosphohistidine phosphatase (PHPT1) was first identified and characterized as a 14-kDa protein in 2002 (7,8). The enzyme can dephosphorylate the phosphohistidinecontaining peptide succinyl-Ala-His(P)-Pro-Phe-p-nitroanilide, E. coli cheA, rabbit ATP-citrase lyase, and the rat ␤-subunit of G proteins (7-10). PHPT1 has been suggested to be highly involved in neuronal function. Unlike most phosphatases it does not require divalent cations for activity. Individual point mutations of conserved histidine and arginine residues determined that Arg 45 , His 53 , and His 102 ma...

Solution structure and catalytic mechanism of human protein histidine phosphatase 1

“…In the first crystal structure of hPHPT1 (PDB code: 2HW4), five formate ions bind to the protein at a relatively large area near residues Lys 21 , His 53 and Arg 78 [12]. It was proposed that His 53 plays a major role in the enzyme activity, and the positively charged side chains of residues Lys 21 and Arg 78 serve as anchors of the substrate as well as helping to stabilize the charge of transition state in the catalysis reaction, based on the structure and mutagenesis results [12]. However, the fact that the R78A mutation only results in ∼ 2-fold decrease in enzyme activity does not really support its role as a substrate anchor.…”

Protein histidine phosphatase 1 negatively regulates CD4 T cells by inhibiting the K + channel KCa3.1

“…The GST-KCa3.1(CT) was phosphorylated by NDPK-B by using [␥-32 P]GTP as described (3). His-PHPT-1(WT) or His-PHPT-1(H53A) were expressed in the expression vector pET-28 in Escherichia coli and purified as described (3,8). Dephosphophorylation was assessed after the addition of His-PHPT-1(WT) or His-PHPT-1(H53A) (2.5 mg per reaction) to the same reaction for 30 min at 37°C.…”

1H, 13C, and 15N resonance assignments of human phosphohistidine phosphatase 1 (PHPT1)

“…Therefore, PHPT1 probably plays an important biological role. Recent site-specific mutagenesis and crystallography studies have revealed the three-dimensional structure of PHPT1 and provided information about its active site (Busam et al 2006;Ma et al 2005). In order to determine the solution structure and study its interaction with substrate proteins, we herein report the nearly complete sequencespecific backbone and side-chain NMR assignments of human PHPT1.…”