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Applied and Environmental Microbiology, September 2007, p. 5648-5652, Vol. 73, No. 17
0099-2240/07/$08.00+0 doi:10.1128/AEM.00052-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Regulation of the mpt Operon in Listeria innocua by the ManR Protein
Junfeng Xue and
Kurt W. Miller*
Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071
Received 9 January 2007/
Accepted 24 June 2007

ABSTRACT
The phosphotransferase system regulation domain (PRD)-containing
activator, ManR, is required for glucose-controlled transcription
of the
mannose
permease
two (
mpt) operon in
Listeria innocua.
His-871 in ManR PRD-II is needed for
mpt repression in glucose-free
media. His-506 in PRD-I is needed for
mpt induction by glucose.

INTRODUCTION
Listeria monocytogenes is a gram-positive, food-borne bacterium
that is responsible for the severe disease listeriosis. Its
close relative,
L. innocua, is the most common nonpathogenic
species isolated from foods.
L. monocytogenes and
L. innocua share many phenotypic properties and differ in the content of
only a few hundred genes (
10).
The principal high-affinity glucose transporter (EIItMan) in L. innocua and L. monocytogenes is encoded by the mpt (mannose permease two) operon (5, 7, 26). EIItMan belongs to the mannose structural family of phosphoenolpyruvate-dependent phosphotransferase system (PTS) permeases (1, 16). EIItMan contains three subunits—IIABMan, IICMan, and IIDMan—that are encoded by the mptA, mptC, and mptD genes (7, 10). Expression of the mpt operon is induced by glucose and mannose (7, 26). EIItMan serves as a docking site for class IIa bacteriocins in Listeria cells (7, 17, 18).
Transcription of mpt is controlled by the sigma factor RpoN (
54), the
54-associated transcription activator ManR, and the Lin0142 protein (7, 19, 26). ManR contains an N-terminal helix-turn-helix DNA binding domain, a
54 interaction domain, a IIAFru domain, and two PTS regulation domains (PRDs) (Fig. 1). ManR probably assists
54 in melting mpt promoter DNA during transcription initiation (3). The regulatory functions of the two PRDs have not been previously analyzed. Lin0142 is related to the CRP-FNR (cyclic AMP receptor protein-fumarate and nitrate reductase regulator) group of transcription factors (26). The role played by Lin0142 in mpt transcription is unknown.
In both gram-positive and gram-negative bacteria, carbon catabolite
repression of catabolic operons is achieved in part by phosphorylation
of conserved histidine residues within the PRDs of transcription
antiterminator and activator proteins (
1,
6,
8,
14,
20-
23).
PRD phosphorylation drives conformational changes that modulate
nucleic acid binding activity (
24). PRD-containing proteins
often are negatively regulated by phosphorylation of one PRD
by the cognate PTS permease in the absence of the transported
sugar and are positively regulated by histidine protein (HPr)-mediated
phosphorylation of the other PRD in the presence of the sugar
and in the absence of glucose (
8,
23). However, studies of closely
related proteins, such as the
Bacillus subtilis LicT and
Escherichia coli BglG antiterminators, have shown that the response (e.g.,
activation) of a protein to PRD phosphorylation is variable
and cannot be easily predicted (
2,
11,
24,
25).
In the present study, we extended research on PRD-containing regulators to Listeria by elucidating the functions of conserved histidines in the PRDs of the L. innocua ManR protein. We also analyzed the general function of ManR in control of mpt transcription. Because L. monocytogenes virulence gene expression is regulated by glucose (8, 9, 12, 15), the present study has ramifications for L. monocytogenes pathogenesis.

Contributions of ManR to mpt transcription.
A
manR in-frame deletion strain, JXD1, was constructed using
L. innocua Lin11 (
26). The chromosomal copy of the
manR gene,
which encodes the 938-amino-acid ManR protein, was replaced
by homologous recombination with a truncated
manR gene, which
encoded only the N-terminal 22 amino acids and C-terminal 41
amino acids of ManR. The in-frame deletion gene was created
by splice-by-overlap extension (SOE) PCR (
13) in plasmid pKSV7
(
4). The PCR primers used for construction of JXD1 are listed
in Table
1.
The effects of gene disruption on
mpt transcription were studied
by real-time reverse transcription-PCR measurement of
mpt mRNA
levels using primers specific for the
mptA (lin0143) gene (
26).
mRNA levels for the lin0142,
manR (lin0778), and
rpoN genes
also were measured to screen for regulatory interactions between
mpt control genes. Cells were grown in Luria-Bertani (LB) media
with or without glucose to an optical density at 600 nm (OD
600)
of 0.3 to 0.4 for RNA isolation. Note that the induction of
the
mpt operon is greater in LB media with glucose at this OD
600 than at the slightly higher OD
600 (0.4 to 0.6) used previously
in a study of
mpt control by the Lin0142 protein (
26). The mRNA
quantitation method used and the primers used for the four genes
and a 16S rRNA endogenous control gene have been described previously
(
26). The REST statistics program was used to compare mRNA levels.
Inactivation of the manR gene reduced the level of mpt mRNA in the JXD1 manR deletion strain 100-fold relative to the basal level measured in the Lin11 control in the absence of glucose (Table 2). In addition, the 17-fold induction of mpt observed in the wild-type strain grown in the presence of glucose was abolished in the deletion mutant. manR inactivation did not significantly affect the transcript levels for the lin0142 and rpoN genes. In addition, the manR deletion strain (and all other mutant strains listed in Table 2) did not exhibit a reduced growth rate in LB media with or without glucose. No changes in the growth rate were observed, possibly because there is more than one glucose transporter in Listeria (5, 7).
The results show that ManR is needed for induction of
mpt transcription
by glucose in
L. innocua, as has previously been demonstrated
in
L. monocytogenes (
7). Interestingly, the
mpt mRNA levels
are reduced at least 1,000-fold (to the background level of
mRNA detection) in the lin0142 knockout strain, G7, in which
lin0142 transcription is abolished due to insertion of Tn
917 into the lin0142 promoter (
26). The combined results indicate
that ManR and Lin0142 are required for the basal, yet significant
level of
mpt transcription that occurs in the absence of glucose.
Some
mpt transcription may still occur in the absence of glucose
because this sugar is the preferred sugar in
Listeria.

Roles of conserved histidines in PRD-I and -II of ManR in regulation of mpt transcription by glucose.
Sequence alignments of
L. innocua ManR and other regulatory
protein PRDs are presented in Fig.
2. The alignments show that
His-506 in PRD-I and His-871 in PRD-II of ManR are highly conserved
along with histidines that are important in regulation of the
activity of proteins such as GlcT, LevR, LicT, and MtlR (
14,
20,
21,
25).
To determine if these histidines are needed for ManR activity,
strains designated
manR-H506A,
manR-H871A, and
manR-H506A/H871A
were constructed, in which one or both residues were replaced
with alanine. The
manR mutant alleles were created in pKSV7
using SOE PCR (Table
1) and were introduced as single copies
into the
L. innocua Lin11 chromosome by homologous recombination.
The JXD1
manR deletion strain was used to construct the
manR-H871A
strain. Another
manR deletion strain, JXD2, in which the N-terminal
161 amino acids and C-terminal 41 amino acids of ManR are preserved,
was used to construct strains
manR-H506A and
manR-H506A/H871A.
In all cases, mutant genes were sequenced in their entirety
and confirmed to differ from the wild type only at the substitution
sites.
The effects of substitution mutations were assessed by measuring the levels of mRNAs for the mpt, lin0142, rpoN, and manR genes by the methods described above (Table 2). In the manR-H506A strain, the mpt mRNA level was the same as the level in Lin11 in the absence of glucose but, unlike the wild-type level, did not increase in the presence of the sugar. In the manR-H871A strain, the mpt mRNA level increased 51.5-fold compared to the level in Lin11 in the absence of glucose. However, a wild-type level of mpt mRNA still was observed in the manR-H871A strain in glucose medium. In the manR-H506A/H871A double mutant, the mpt mRNA level was 8.6-fold higher than the level in Lin11 in the medium without glucose and was the same as the Lin11 basal level in glucose medium. The data generally indicate that His-506 is required for the activation of ManR and induction of mpt transcription in the presence of glucose. His-871 is needed for the inactivation of ManR and a reduction in mpt transcription in the absence of glucose but is not needed for ManR activation in glucose medium. Note that the mRNA levels for the lin0142, rpoN, and the manR mutant genes were unaffected in all strains.
Alterations in mpt transcription are unlikely to be caused by changes in the levels of mutant ManR proteins in the strains. The protein synthesis rates should not be affected because the mutation sites are far removed from the 5' ends of the transcripts and the manR mRNA levels are the same as the wild-type levels (Table 2). For the relatively inactive proteins that contain the H506A substitution, the mpt transcript levels did not fall below the uninduced level observed in Lin11, suggesting that this substitution does not strongly destabilize the protein. If a mutation rendered a protein highly unstable or completely nonfunctional, the level of mpt mRNA would be greatly reduced, as in the manR deletion strain. It also is unlikely that proteins with the H871A substitution accumulate to greater-than-normal levels in cells and thereby elevate mpt transcription. In this regard, the level of mpt mRNA returned to normal in the single-mutant strain grown in the presence of glucose and was equivalent to the basal uninduced level in the double-mutant strain in glucose medium, probably due to the H506A mutation. Instead, the results suggest that ManR specific activity is altered by the alanine substitutions.

Model for mpt regulation.
A model for regulation of
mpt operon transcription by PTS phosphorylation
of ManR is presented in Fig.
3. The model is based on the data
described above and on a large number of studies of PTS operon
regulation in gram-positive bacteria. Below, these studies are
summarized first, with a focus on work conducted with the 38%
identical
54-associated activator LevR, which controls the
lev operon in
B. subtilis (
7,
14), the LevR-like regulator EsuR,
which controls the
esu operon in
Lactobacillus casei (
27), and
the GlcT antiterminator, which controls the
ptsGHI operon in
B. subtilis (
20).
In the absence of inducer transport, the transcription of the
lev and
esu operons is repressed by EIIB phosphorylation of
LevR and EsuR histidines in the PRD-IIs of these proteins (
14,
27). The targeted histidine in LevR, His-869, corresponds to
His-871 in ManR (Fig.
2). Transcription of the
lev operon actually
increases to a level above the wild-type induced level when
nonphosphorylatable alanine is substituted at this site for
unknown reasons (
14). In contrast to ManR, His-506 of LevR PRD-I,
which corresponds to His-506 in ManR, is not needed for LevR
activation by fructose. In the GlcT antiterminator, IIB
Glc phosphorylation
of His-104 in PRD-I in the absence of glucose strongly inactivates
GlcT and represses
ptsGHI transcription (
20). In contrast, HPr
phosphorylation of His-210 in PRD-II in the presence of glucose
slightly activates the protein. Note that the order of the PRDs
is reversed within the polypeptide chains of antiterminators
and activators. As occurs with LevR, replacement of His-104
in GlcT with alanine leads to greater-than-wild-type induction
of
ptsGHI transcription (
20).
Based on our data showing that His-871 must be present in ManR PRD-II for repression of mpt in the absence of glucose, we propose that this site is phosphorylated by IIABMan in the absence of glucose and phosphorylation inactivates the protein, as occurs in the LevR, EsuR, and GlcT regulators (Fig. 3). This idea is bolstered by the observation that the amount of mpt mRNA reaches a greatly elevated level in the H871A single-substitution mutant grown in the absence of glucose (Table 2). When glucose is being transported, we propose that wild-type ManR molecules are not phosphorylated at His-871, and this increases the activity of ManR and mpt transcription, as also occurs with other regulators. In the H871A mutant strain grown in the absence of glucose, the amount of mpt mRNA increases to a level above the level in the wild-type strain during glucose induction because none of the copies of the ManR protein can be phosphorylated at His-871.
mRNA measurements showed that both single- and double-mutant ManR proteins containing the H506A substitution retain only the basal capacity for transcription of the mpt operon in glucose medium (Table 2). Work performed with GlcT indicates that the homologous histidine in this antiterminator can be phosphorylated by HPr (20, 22). Our finding that the mpt mRNA level is reduced
6-fold in the H506A/H871A double mutant compared to the H871A single mutant in LB medium lacking glucose suggests that ManR is activated by phosphorylation at His-506. Furthermore, the threefold decline in the mpt mRNA level observed when the H871A mutant was grown in glucose medium, in which phosphorylation at this site should have been reduced, also suggests that ManR is activated by phosphorylation on His-506.
In conclusion, based on the data described above we propose that although the wild-type ManR protein probably is phosphorylated by HPr on His-506 both in the absence and in the presence of glucose (8, 22, 23), the dual-phosphorylated protein that exists in the absence of glucose is inactive, while the single-phosphorylated species that occurs in glucose medium is active (Fig. 3). In other words, the ratio of phosphorylated residues to unphosphorylated residues in ManR determines its activity. The phosphorylation that occurs at His-871 in the absence of glucose appears to exert a dominant effect and down-regulates the activity of the protein. Additional studies are required to clarify why Lin0142 is needed in addition to ManR for activation of RNA polymerase at the
54-controlled mpt promoter.

ACKNOWLEDGMENTS
We acknowledge financial support from the University of Wyoming.

FOOTNOTES
* Corresponding author. Mailing address: Department of Molecular Biology, University of Wyoming, 1000 E. University Avenue, Dept. 3944, Laramie, WY 82071-3944. Phone: (307) 766-2037. Fax: (307) 766-5098. E-mail:
kwmiller{at}uwyo.edu 
Published ahead of print on 6 July 2007. 

REFERENCES
1 - Barabote, R. D., and M. H. Saier, Jr. 2005. Comparative genomic analyses of the bacterial phosphotransferase system. Microbiol. Mol. Biol. Rev. 69:608-634.[Abstract/Free Full Text]
2 - Ben-Zeev, E., L. Fux, O. Amster-Choder, and M. Eisenstein. 2005. Experimental and computational characterization of the dimerization of the PTS-regulation domains of BglG from Escherichia coli. J. Mol. Biol. 347:693-706.[CrossRef][Medline]
3 - Buck, M., M. T. Gallegos, D. J. Studholme, Y. Guo, and J. D. Gralla. 2000. The bacterial enhancer-dependent
54 (
N) transcription factor. J. Bacteriol. 182:4129-4136.[Free Full Text] 4 - Camilli, A., L. G. Tilney, and D. A. Portnoy. 1993. Dual roles of plcA in Listeria monocytogenes pathogenesis. Mol. Microbiol. 8:143-157.[Medline]
5 - Christensen, D. P., and R. W. Hutkins. 1994. Glucose uptake by Listeria monocytogenes Scott A and inhibition by pediocin JD. Appl. Environ. Microbiol. 60:3870-3873.[Abstract/Free Full Text]
6 - Commichau, F. M., K. Forchhammer, and J. Stulke. 2006. Regulatory links between carbon and nitrogen metabolism. Curr. Opin. Microbiol. 9:167-172.[CrossRef][Medline]
7 - Dalet, K., Y. Cenatiempo, P. Cossart, and Y. Hechard. 2001. A
54-dependent PTS permease of the mannose family is responsible for sensitivity of Listeria monocytogenes to mesentericin Y105. Microbiology 147:3263-3269.[Abstract/Free Full Text] 8 - Deutscher, J. R., C. Francke, and P. W. Postma. 2006. How phosphotransferase system-related protein phosphorylation regulates carbohydrate metabolism in bacteria. Microbiol. Mol. Biol. Rev. 70:939-1031.[Abstract/Free Full Text]
9 - Gilbreth, S. E., A. K. Benson, and R. W. Hutkins. 2004. Catabolite repression and virulence gene expression in Listeria monocytogenes. Curr. Microbiol. 49:95-98.[Medline]
10 - Glaser, P., L. Frangeul, C. Buchrieser, C. Rusniok, A. Amend, F. Baquero, P. Berche, H. Bloecker, P. Brandt, T. Chakraborty, A. Charbit, F. Chetouani, E. Couve, A. de Daruvar, P. Dehoux, E. Domann, G. Dominguez-Bernal, E. Duchaud, L. Durant, O. Dussurget, K. D. Entian, H. Fsihi, F. Garcia-del Portillo, P. Garrido, L. Gautier, W. Goebel, N. Gomez-Lopez, T. Hain, J. Hauf, D. Jackson, L. M. Jones, U. Kaerst, J. Kreft, M. Kuhn, F. Kunst, G. Kurapkat, E. Madueno, A. Maitournam, J. M. Vicente, E. Ng, H. Nedjari, G. Nordsiek, S. Novella, B. de Pablos, J. C. Perez-Diaz, R. Purcell, B. Remmel, M. Rose, T. Schlueter, N. Simoes, A. Tierrez, J. A. Vazquez-Boland, H. Voss, J. Wehland, and P. Cossart. 2001. Comparative genomics of Listeria species. Science 294:849-852.[Abstract/Free Full Text]
11 - Greenberg, D. B., J. Stulke, and M. H. Saier, Jr. 2002. Domain analysis of transcriptional regulators bearing PTS regulatory domain. Res. Microbiol. 153:519-526.[Medline]
12 - Herro, R., S. Poncet, P. Cossart, C. Buchrieser, E. Gouin, P. Glaser, and J. Deutscher. 2005. How seryl-phosphorylated HPr inhibits PrfA, a transcription activator of Listeria monocytogenes virulence genes. J. Mol. Microbiol. Biotechnol. 9:224-234.[CrossRef][Medline]
13 - Horton, R. M., Z. L. Cai, S. N. Ho, and L. R. Pease. 1990. Gene splicing by overlap extension: tailor-made genes using the polymerase chain reaction. BioTechniques 8:528-535.[Medline]
14 - Martin-Verstraete, I., V. Charrier, J. Stulke, A. Galinier, B. Erni, G. Rapoport, and J. Deutscher. 1998. Antagonistic effects of dual PTS-catalysed phosphorylation on the Bacillus subtilis transcriptional activator LevR. Mol. Microbiol. 28:293-303.[CrossRef][Medline]
15 - Milenbachs, A. A., D. P. Brown, M. Moors, and P. Youngman. 1997. Carbon-source regulation of virulence gene expression in Listeria monocytogenes. Mol. Microbiol. 23:1075-1085.[CrossRef][Medline]
16 - Postma, P. W., J. W. Lengeler, and G. R. Jacobson. 1993. Phosphoenolpyruvate:carbohydrate phosphotransferase systems of bacteria. Microbiol. Rev. 57:543-594.[Abstract/Free Full Text]
17 - Ramnath, M., M. Beukes, K. Tamura, and J. W. Hastings. 2000. Absence of a putative mannose-specific phosphotransferase system enzyme IIAB component in a leucocin A-resistant strain of Listeria monocytogenes, as shown by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Appl. Environ. Microbiol. 66:3098-3101.[Abstract/Free Full Text]
18 - Ramnath, M., S. Arous, A. Gravesen, J. W. Hastings, and Y. Hechard. 2004. Expression of mptC of Listeria monocytogenes induces sensitivity to class IIa bacteriocins in Lactococcus lactis. Microbiology 150:2663-2668.[Abstract/Free Full Text]
19 - Robichon, D., E. Gouin, M. Debarbouille, P. Cossart, Y. Cenatiempo, and Y. Hechard. 1997. The rpoN (
54) gene from Listeria monocytogenes is involved in resistance to mesentericin Y105, an antibacterial peptide from Leuconostoc mesenteroides. J. Bacteriol. 179:7591-7594.[Abstract/Free Full Text] 20 - Schmalisch, M. H., S. Bachem, and J. Stulke. 2003. Control of the Bacillus subtilis antiterminator protein GlcT by phosphorylation. J. Biol. Chem. 278:51108-51115.[Abstract/Free Full Text]
21 - Stulke, J., M. Arnaud, G. Rapoport, and I. Martin-Verstraete. 1998. PRD—a protein domain involved in PTS-dependent induction and carbon catabolite repression of catabolic operons in bacteria. Mol. Microbiol. 28:865-874.[CrossRef][Medline]
22 - Stulke, J., and W. Hillen. 2000. Regulation of carbon catabolism in Bacillus species. Annu. Rev. Microbiol. 54:849-880.[CrossRef][Medline]
23 - Titgemeyer, F., and W. Hillen. 2002. Global control of sugar metabolism: a Gram-positive solution. Antonie Leeuwenhoek 82:59-71.[CrossRef][Medline]
24 - van Tilbeurgh, H., and N. Declerck. 2001. Structural insights into the regulation of bacterial signaling proteins containing PRDs. Curr. Opin. Struct. Biol. 11:685-693.[CrossRef][Medline]
25 - van Tilbeurgh, H., D. Le Coq, and N. Declerck. 2001. Crystal structure of an activated form of the PTS regulation domain from the LicT transcriptional antiterminator. EMBO J. 20:3789-3799.[CrossRef][Medline]
26 - Xue, J., I. Hunter, T. Steinmetz, A. Peters, B. Ray, and K. W. Miller. 2005. Novel activator of mannose-specific phosphotransferase system permease expression in Listeria innocua, identified by screening for pediocin AcH resistance. Appl. Environ. Microbiol. 71:1283-1290.[Abstract/Free Full Text]
27 - Yebra, M. J., R. Viana, V. Monedero, J. Deutscher, and G. Perez-Martinez. 2004. An esterase gene from Lactobacillus casei cotranscribed with genes encoding a phosphoenolypyruvate:sugar phosphotransferase system and regulated by a LevR-like activator and
54 factor. J. Mol. Microbiol. Biotechnol. 8:117-128.[CrossRef][Medline]
Applied and Environmental Microbiology, September 2007, p. 5648-5652, Vol. 73, No. 17
0099-2240/07/$08.00+0 doi:10.1128/AEM.00052-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
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