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Journal of Bacteriology, April 2008, p. 2629-2632, Vol. 190, No. 7
0021-9193/08/$08.00+0 doi:10.1128/JB.01722-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Novel Monofunctional Histidinol-Phosphate Phosphatase of the DDDD Superfamily of Phosphohydrolases
Hyun Sook Lee,
Yona Cho,
Jung-Hyun Lee, and
Sung Gyun Kang*
Korea Ocean Research & Development Institute, Ansan P.O. Box 29, Seoul 425-600, Republic of Korea
Received 28 October 2007/
Accepted 11 January 2008

ABSTRACT
The TON_0887 gene was identified as the missing histidinol-phosphate
phosphatase (HolPase) in the hyperthermophilic archaeon "
Thermococcus onnurineus" NA1. The protein contained conserved motifs of the
DDDD superfamily of phosphohydrolase, and the recombinantly
expressed protein exhibited strong HolPase activity. In this
study, we functionally assessed for the first time the monofunctional
DDDD-type HolPase, which is organized in the gene cluster.

TEXT
Histidinol-phosphate phosphatase (HolPase; EC 3.1.3.15) catalyzes
the eighth step in the histidine biosynthesis pathway, the dephosphorylation
of histidinol-phosphate to histidinol, the direct precursor
of histidine. HolPases belonging to the PHP (polymerase and
histidinol phosphatase) superfamily in
Bacillus subtilis, Saccharomyces cerevisiae, and
Thermus thermophilus have been functionally
characterized (
15,
17,
19). The HolPases as members of the DDDD
phosphohydrolase/phosphotransferase superfamily have been revealed
to be bifunctional, with the C-terminal domain exhibiting imidazole
glycerol-phosphate dehydratase (IGPD; EC 4.2.1.19) activity
(
8,
12,
16). In many organisms across all three kingdoms (bacteria,
archaea, and eukaryotes), there is no report on the functional
assessment of the monofunctional DDDD-type HolPase, whereas
monofunctional IGPDs have been identified from fungi, plants,
archaea, and some bacteria (
11,
18,
20,
25).
In the sequenced archaeal genome of "Thermococcus onnurineus" NA1 (2; H. S. Lee and S. G. Kang, submitted for publication), most genes encoding the enzymes of the histidine biosynthesis pathway could be identified by sequence similarity with their counterparts, but the only gene encoding HolPase appeared to be missing. The analysis of the organization of his genes in "T. onnurineus" NA1 revealed that they are arranged in a compact cluster whose relative gene order, hisGDBHAF(IE)C, resembles that of the complete enterobacterial his operon, hisGDC(NB)HAF(IE) (1, 7) (Fig. 1). The same gene organization as that of "T. onnurineus" NA1 was also found in two bacterial genomes, those of Oceanobacillus iheyensis (26) and Lactobacillus plantarum (14), and in two hyperthermophilic-archaeal genomes, those of Thermococcus kodakarensis (10) and Pyrococcus furiosus (23), by the Sequence Similarity Database (SSDB) gene cluster search program (http://www.genome.jp) of the Kyoto Encyclopedia of Genes and Genomes (KEGG) (4, 13). The gene organization exhibited a translocation of the hisC gene with respect to the Escherichia coli arrangement, moving from downstream of hisD to downstream of his(IE) at the end of the cluster. Compact his gene clusters, with a hisC gene next to his(IE) or isolated from the cluster, have been detected in only a few genomes. In those cases, most monofunctional HolPases are not clustered with other his genes but are present elsewhere in the chromosome (6). It is peculiar, therefore, that the genes encoding PHP-type HolPases are located immediately downstream of hisG, encoding ATP phosphoribosyltransferase, which is next to hisZ, encoding the ATP phosphoribosyltransferase regulatory subunit in the cases of O. iheyensis and L. plantarum.
Because all three monofunctional IGPDs were present in the gene
clusters of "
T. onnurineus" NA1,
T. kodakarensis, and
P. furiosus,
we attempted to search for the monofunctional HolPases. By the
alignment of
his genes as shown in Fig.
1, three open reading
frames (ORFs) which are conserved in three genomes and located
downstream of the
hisC genes were found. They showed significant
homology with each other (52.5 to 53.8% identity) (Fig.
2).
The ORF of
P. furiosus (PF1666) was not assigned a function
(hypothetical protein), but those of "
T. onnurineus" NA1 (TON_0887)
and
T. kodakarensis (TK0251) were predicted to be hydrolases
belonging to the haloacid dehalogenase-like hydrolase (HAD)
superfamily. A homology search of the ORFs by the Basic Local
Alignment Search Tool (BLAST) program against the nonredundant
protein database from the NCBI did not yield any significant
match. Those three ORFs were the strongest candidate genes for
the missing HolPase genes in three genomes, not because of their
distinctive localization but because they are HAD members that
contain three conserved motifs, including four invariant aspartate
residues found in the DDDD superfamily (Fig.
2).
To determine whether the candidate gene, TON_0887, in "
T. onnurineus"
NA1 is a bona fide HolPase, we expressed the gene in
Escherichia coli. The full-length TON_0887 gene was amplified by PCR with
the primers sense-NdeI (5'-CGACCCGG
CATATGAAGTGGATCATCTTCGACGTTG-3'
[the italicized bases indicate the NdeI site]) and antisense-SalI
(5'-CTCCACAT
GTCGACCCCCAATAAGTTCTCCAATAATTC-3' [the italicized
bases indicate the SalI site]) from genomic DNA isolated by
standard procedures (
24). The amplified DNA fragments were digested
with NdeI and SalI and then ligated into the NdeI/SalI-digested
pET-24a(+) vector (Novagen, Madison, WI).
E. coli Rosetta(DE3)pLysS
(Stratagene, La Jolla, CA) was transformed with the constructed
plasmid to express a recombinant protein. The His
6 tag fusion
protein was purified to homogeneity using a combination of Talon
metal affinity column chromatography (BD Biosciences Clontech,
Palo Alto, CA) and Superdex 200 10/300 GL column chromatography
(Amersham Biosciences, Piscataway, NJ). The buffer of the protein
was then exchanged with 50 mM Tris-HCl buffer (pH 8.0), which
includes 10% glycerol, using Centricon YM-10 (Millipore, Bedford,
MA). Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis
showed that the 30-kDa protein, which is the expected size of
the fusion product comprising the 28.1-kDa protein and the 1.7-kDa
peptide corresponding to the VDKLAAALEH
6 (His
6 tag) at the C-terminal
region of the protein, was the major component of the purified
sample (Fig.
3). Gel filtration under nondenaturing conditions
showed a protein peak corresponding to a molecular mass of 39
kDa, implying that the protein exists as a monomer in solution
(data not shown).
To prove the functionality of the TON_0887-derived protein as
the HolPase, the ability to release inorganic phosphate from
histidinol-phosphate was investigated (
3,
21). The protein displayed
strong HolPase activity in the presence of Mg
2+, Mn
2+, Ni
2+,
Co
2+, or Cu
2+, as expected from the requirement of metal as
a cofactor for catalysis, because TON_0887, as a member of the
DDDD superfamily, possesses conserved residues in motifs I and
III, which interact with a metal ion and are essential for activity
(Fig.
2). The HolPase activity was buffer dependent and evaluated
to be maximal at pH 6.5 (data not shown). However, the protein
did not show any phosphatase activity against a general phosphatase
substrate,
p-nitrophenyl phosphate. Furthermore, with 26 various
natural phosphatase substrates (Sigma, St. Louis, MO), including
17 ribo- and deoxyribonucleoside 5'- or 3'-mono-, di-, or triphosphates,
5 carbohydrate phosphates, 2 amino acid phosphates, and 2 small
phosphates (pyrophosphate and acetyl phosphate), no significant
activity was detected, except for AMP, fructose 6-phosphate,
and phosphoserine. Kinetic parameters for the enzyme with histidinol-phosphate,
AMP, fructose 6-phosphate, and phosphoserine were determined
and are presented in Table
1.
Km values for AMP, fructose 6-phosphate,
and phosphoserine are 1 order of magnitude higher than that
for histidinol-phosphate, which shows that HolPase has higher
apparent substrate affinity for histidinol-phosphate. Furthermore,
the enzyme displayed a 2- or 3-order-of-magnitude increase in
catalytic efficiency (
kcat/
Km) with histidinol-phosphate compared
with the efficiencies of the above-mentioned substrates, implying
that the enzyme is highly specific for histidinol-phosphate.
The kinetic parameters were affected by metal ions (Table
1).
The enzyme showed a higher
Km in the presence of Mg
2+ or Ni
2+ than in the presence of Co
2+ or Mn
2+. In the presence of Mg
2+,
Ni
2+, or Co
2+, the enzyme had similar
kcat/
Km ratios (3
x 10
6 to 5
x 10
6 M
–1 s
–1), whereas the activity was two-
to threefold higher in the presence of Mn
2+. Regardless of the
metal ions, the substrate preference of the enzyme remained
unchanged (data not shown). The
kcat/
Km ratio of the enzyme
toward histidinol-phosphate in the presence of Mn
2+ was comparable
to that of the N-terminal domain of
E. coli HisB, a bifunctional
DDDD-type enzyme, as a result of the equal contributions of
the respective
kcat and
Km values (
22). TON_0887 was verified
to play the same role as
hisN, for which such enzymatic activity
has actually been demonstrated, thus completing the
his gene
cluster,
hisGDBHAF(
IE)
CN. The highly homologous genes PF1666
and TK0251 from
P. furiosus and
T. kodakarensis, respectively,
are highly likely to encode HolPases, as is consistent with
the previous report which designated PF1666 as
hisN next to
hisC at the end of the
his gene cluster in
P. furiosus (
9).
Gene disruption studies and biochemical characterization of
these orthologues would fortify their putative activities.
This study is the first functional assessment of the monofunctional
DDDD-type HolPase. Furthermore, HolPases in "
T. onnurineus"
NA1,
T. kodakarensis, and
P. furiosus are the first indication
of monofunctional DDDD-type HolPases being organized in the
his gene cluster. For the gene organization
hisGDBHAF(
IE)
CN,
it is not easy to explain how
hisN got into the final position
at present. It is possible that
hisN was translocated from the
middle to the end of gene cluster along with
hisC before
hisN and
hisB were fused to a single bifunctional polypeptide, or
perhaps
hisN was recruited in the already constructed cluster
hisGDBHAF(
IE)
C, where
hisC had already been translocated. There
are only a few cases for the occurrence of
hisN(
Z)
GDBHAF(
IE)
C,
where
hisN is a PHP-type HolPase, but no
hisNGDBHAF(
IE) or
hisGDBHAF(
IE)
N has been detected until now. The gene evolution of
hisC as well
as that of
hisN might explain the gene organization.
The comparative genome analysis of his gene clusters in the 31 finished genomes revealed that TON_0887 is very distinct, as it is conserved only in some Thermococcales, although the conservation patterns of most other genes were very similar (H. S. Lee and S. G. Kang, unpublished data), suggesting that orthologous HolPases in other archaea might possess novel sequences.
In conclusion, we have predicted the missing HolPase gene in the histidine biosynthesis pathway in the hyperthermophilic archaeon "T. onnurineus" NA1 by analyzing its primary sequence and gene organization and verified the functionality of the gene by expression, purification, and biochemical analyses, which indicate that it is the first monofunctional DDDD-type HolPase in the gene cluster.
Nucleotide sequence accession number.
The TON_0887 sequence has been deposited in GenBank under accession no. EU487258.

ACKNOWLEDGMENTS
We thank V. Jo Davisson (Purdue University) for providing us
with histidinol-phosphate.
This work was supported by the KORDI in-house program (PE97802) and the Marine and Extreme Genome Research Center Program of the Ministry of Maritime Affairs and Fisheries, Republic of Korea, and by a Korea Research Foundation grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (KRF-2006-532-C00011).

FOOTNOTES
* Corresponding author. Mailing address: Korea Ocean Research & Development Institute, Ansan P.O. Box 29, Seoul 425-600, Republic of Korea. Phone: 82-31-400-6241. Fax: 82-31-406-2495. E-mail:
sgkang{at}kordi.re.kr 
Published ahead of print on 25 January 2008. 
These authors contributed equally to this work. 

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Journal of Bacteriology, April 2008, p. 2629-2632, Vol. 190, No. 7
0021-9193/08/$08.00+0 doi:10.1128/JB.01722-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.