Transmembrane Topology of AgrB, the Protein Involved in the
Post-translational Modification of AgrD in Staphylococcus
aureus*
Linsheng
Zhang
,
Lillian
Gray,
Richard P.
Novick§, and
Guangyong
Ji¶
From the Department of Microbiology and Immunology,
Uniformed Services University of the Health Sciences, Bethesda,
Maryland 20814 and the § Molecular Pathogenesis
Program, Skirball Institute of Biomolecular Medicine, New York
University Medical Center, New York, New York 10016
The accessory gene regulator (agr) of
Staphylococcus aureus is the central regulatory system that
controls the gene expression for a large set of virulence factors. This
global regulatory locus consists of two transcripts: RNAII and RNAIII.
RNAII encodes four genes (agrA, B,
C, and D) whose gene products assemble a quorum sensing system. RNAIII is the effector of the Agr response. Both the
agrB and agrD genes are essential for the
production of the autoinducing peptide, which functions as a signal for
the quorum sensing system. In this study, we demonstrated the
transmembrane nature of AgrB protein in S. aureus. A
transmembrane topology model of AgrB was proposed based on AgrB-PhoA
fusion analyses in Escherichia coli. Two hydrophilic
regions with several highly conserved positively charged amino acid
residues among various AgrBs were found to be located in the
cytoplasmic membrane as suggested by PhoA-AgrB fusion studies. However,
this finding is inconsistent with the putative transmembrane profile of
AgrB by computer analysis. Furthermore, we detected an intermediate
peptide of processed AgrD from S. aureus cells
expressing AgrB and a 6 histidine-tagged AgrD. These results provide
direct evidence that AgrB is involved in the proteolytic processing of
AgrD. We speculate that AgrB is a novel protein with proteolytic enzyme
activity and a transporter facilitating the export of the processed
AgrD peptide.
*
This work was supported by National Institutes of Health
Grant RO1AI46445 (to G. J.) and a USUHS grant (to G. J.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
The amino acid sequences of these proteins can be accessed
through NCBI Protein Database under NCBI accession numbers CAA36781, AAB63264, AAB63267, AAG03055, AAC38295, and AAA71976.
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