Page 120 - The Biochemistry of Inorganic Polyphosphates

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Functions of polyphosphate and polyphosphate-dependent enzymes
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made on the essential role of polyphosphate kinase and PolyP in bacterial pathogenesis
(Kornberg, 1999; Kornberg et al., 1999).
PolyP was shown to be a component of the cell capsule of Neisseria. These capsu-
lar PolyPs were about a half of the cellular content of PolyP (Tinsley et al., 1993). The
polyphosphate kinase deficient mutant of Neisseria had a reduced PolyP pool and a lower
pathogenicity than the wild-type strain (Tinsley and Gotschlich, 1995).
The effects on the cell-envelope functions of mutations in the ppk1 gene encoding the
polyphosphate kinase 1 were studied (Rashid and Kornberg, 2000; Rashid et al., 2000a,b).
The ppk1 null mutants were prepared from Pseudomonas aeruginosa, Vibrio cholerae,
Salmonella enterica, E. coli and Klebsiella pneumoniae, and the motility of these mutants
was compared with that of the corresponding wild-type strains on swim plates (1 % tryptone,
0.5 NaCl, 0.3 % agar). The swim areas were decreased in ppk null mutants to 13–79 % of
the corresponding areas of wild strains. When the mutants were transformed by PPK-
expressing plasmids, the motility was completely restored. Electron microscopy revealed
that the mutants possessed apparently intact flagella. Thus, the effect of the mutation on
swimming motility was proposed to be due to altered functioning of the flagella (Rashid
etal.,2000a).Inaliquidculture,however,theppkmutantsweremotile(Rashidetal.,2000a).
The ppk mutant of P. aeruginosa was also deficient in type-IV pili-mediated twitching
and in swarming motility (Rashid and Kornberg, 2000). Some suggestions on the molecular
mechanisms of PolyP– PPK action in motility were made (Rashid and Kornberg, 2000).
These included the possible role of PolyP in the phosphorylation of Che-Y-like proteins or
modulation of the Ca 2+ level (Rashid and Kornberg, 2000).
The role of PolyP in the cell envelope of prokaryotes may be connected with their
anionic properties, important for providing the negative charge of this compartment. In
addition, PolyPs may affect the cell-envelope functions by gene activity regulation, as will
be discussed below.

7.5.2 Polyphosphates in the Cell Envelopes of Eukaryotes

PolyPs are present in the cell envelopes of the lower eukaryotes, where their contents
may vary depending on the cultivation conditions. PolyP was found at first in the cell
envelope of Neurospora crassa (Krascheninnikov et al., 1967; Kulaev et al., 1970) and En-
domyces magnusii (Kulaev et al., 1967; Kulaev and Afanasieva, 1970). This high-molecular-
weight PolyP was located outside of the cell, adjacent to the outer side of the cytoplasmic
membrane.
PolyP was revealed outside of the plasma membrane of the yeast Kluyveromyces marx-

ianus by fluorescence of 4 6-diamidino-2-phenylindole (Tijssen et al., 1982), by osmotic
shock treatment (Tijssen et al., 1983), by decrease of the 31 P NMR signal under UO 2 2+
binding (Tijssen and van Steveninck, 1984), and by lead staining and X-ray microanalysis
(Tijssen and Van Steveninck, 1985). When the cells of K. marxianus were subjected to os-
motic shock, they released a limited amount of PolyP into the medium, which represented
about 10 % of the total cellular content. The procedure of osmotic shock caused no sub-
+
stantial membrane damage, as was judged from limited K and unimpaired cell viability.
The released PolyP fraction differed from other cellular PolyPs by the higher chain length
and the lower metabolic turnover rate (Tijssen et al., 1983).