Page 124 - The Biochemistry of Inorganic Polyphosphates

WU095/Kulaev
WU095-07
Functions of polyphosphate and polyphosphate-dependent enzymes
108 March 9, 2004 15:39 Char Count= 0
for ATP regeneration when using PolyP. It was suggested that polyphosphate kinase in the
degradosome maintained an appropriate micro-environment, removing inhibitory PolyPs
and regenerating ATP (Blum et al., 1997).
In addition, PolyPs are most likely involved in the regulation of enzyme activities by
participation in their phosphorylation. A protein phosphorylation process, using not ATP but
high-polymer PolyPs, was revealed in the archae Sulfolobus acidocaldarius (Skorko, 1989).
Tripolyphosphate was observed to be a phosphodonor of selective protein phosphorylation
of rat liver microsomal membrane (Tsutsui, 1986).

7.7 Gene Activity Control, Development
and Stress Response

7.7.1 In Prokaryotes
The involvement of PolyPs in the regulation of enzyme activities and expression of large
groups of genes is the basis of their effects on survival under stress conditions and adaptation
to the stationary-growth phase. The genes encoding the enzymes of PolyP metabolism in
E. coli were proposed to form a phosphate regulon together with a number of other genes,
the products of which are involved in phosphate metabolism and transport (Nesmeyanova
et al., 1975 a,b). At present, the interrelation of PolyP metabolism and the activities of PHO
and PHOB regulons is supplemented with new details. A number of works of A. Kornberg
and co-workers show that polyphosphate kinase and PolyPs synthesized by this enzyme
play the key role in the transition of bacteria from active growth to the stationary phase, as
well as in their survival in the stationary phase and under stress. These are summarized in a
number of publications (Kornberg, 1999; Rao and Kornberg, 1999; Kornberg et al., 1999).
It should be noted that in bacteria there is a tight interrelation between PolyP and a
signal compound, guanosine 3,5-bispyrophosphate (ppGpp). PolyP accumulation requires
the functional PHOB gene and higher levels of (p)ppGpp. The latter serves as an alarmon in
prokaryotes, which distributes and coordinates different cellular processes according to the
nutritional potential of the growth medium (Svitil et al., 1993; Nystrom, 1994, 2003; Faxen
and Isaksson, 1994; Schreiber et al., 1995). This polyfunctional signalling compound is
accumulated in bacteria in response to either amino acid or energy source starvation (Svitil
et al., 1993; Nystrom, 1994). The major role in the control of its level in E. coli is played by

the genes spoT (encoding guanosine 3 5 -bis(diphosphate) 3 -pyrophosphohydrolase and,
probably, guanosine 3 5 -bis(diphosphate) synthetase, designated as PSII) and relA (en-

coding ppGpp synthetase I, PSI) (Gentry and Cashel, 1996). Activation of RelA results in
a global change of cellular metabolism, including enhanced expression of the stationary-
phase sigma factor RpoS. The product of the gene gppA participates in the hydrolysis of
this compound (Keasling et al., 1993). When the intracellular level of ppGpp in E. coli was
enhanced by expression of truncated relA, encoding the more catalytically active ppGpp
synthetase, the rate of protein synthesis was inhibited to the level characteristic of amino
acid starvation (Svitil et al., 1993). The stringent response genes relA and spoT are impor-
tant for Escherichia coli biofilms-formation slow-growth conditions (Balzer and McLean,
2002). Inhibition of transcription of ribosomal RNA in Escherichia coli upon amino acid