Affiliation:
1. Department of Oral Biology, State University of New York, Buffalo, New York 14214,1 and
2. Department of Biological Sciences, University of Central Lancashire, Preston PR1 2HE, United Kingdom2
Abstract
ABSTRACT
SGP (for
Streptococcus
GTP-binding protein) is a
Streptococcus mutans
essential GTPase which has significant sequence identity to the previously identified
Escherichia coli
Era protein and to numerous other prokaryotic GTPase proteins of unknown function. Recent studies in our laboratory have addressed the possible role of SGP in the stress response of the oral pathogen
S. mutans
. Here we report that during growth in the early stationary phase, and in response to elevated temperatures or acidic pH, the distribution of SGP between the cytoplasm and the membranes of
S. mutans
cells varies. Immunoblot analysis of soluble and membrane protein fractions collected from the mid-log and early stationary growth phases of bacterial populations grown at normal temperature (37°C) and at the elevated temperature of 43°C, or at acidic pH, demonstrated that the total amount of SGP increased with the age of the bacterial culture, elevated temperature, or acidic pH. Furthermore, it was established that a substantial amount of SGP is associated with the membrane fraction under stress conditions. In order to investigate the physiological role of SGP, we constructed an
S. mutans
strain capable of chromosomal
sgp
antisense RNA expression, which interferes with the normal information processing of the
sgp
gene. Utilizing this strain, we determined conditions whereby the streptococcal cells can be depleted of SGP, thus avoiding the problem of constructing a conditional lethal system. From the results of measurements of the nucleotide pools extracted from the antisense strain and its isogenic counterpart, we propose that one of the physiological roles of SGP is regulation and modulation of the GTP/GDP ratio under different growth conditions. Moreover, we observed that in SGP-depleted cells the levels of glucan-binding protein A (GbpA) substantially increased, suggesting that GbpA may have stress response-related physiological functions. Finally, the potential applications of the antisense RNA approach that we employed are discussed.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
53 articles.
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