Biology Reference
In-Depth Information
The members of this protein family are characterized by the presence of
two transmembrane regions (TM1 and TM2) flanking a large hydrophilic
loop located in the periplasmatic side of the plasma membrane (
Cuth-
bertson et al., 2009
;
Morona et al., 2000
). In addition, they also contain
a proline- and glycine-rich domain preceding and overlapping the TM2
(
Cuthbertson et al., 2009
;
Morona, Purins, Tocilj, Matte, & Cygler, 2009
).
The PCP proteins can be distinguished according to the type of poly-
saccharide, association with the Wzy or ABC-dependent assembly and
export pathways, coiled-coil prediction profile and presence of charac-
teristic domains (
Fig. 7.2
) (
Morona et al., 2009
,
2000
). The PCP-1 family
comprises the Wzz proteins, which participate in the biosynthesis of the
O-antigen of LPS and the enterobacterial common antigen by the Wzy-
dependent pathway (
Morona et al., 2009
,
2000
;
Whitfield, 2010
). The
PCP-2 refers to the proteins involved in the polymerization and export
of high molecular polysaccharides, including the EPS, also following the
Wzy-dependent pathway. The PCP-2 of Gram-negative bacteria, includ-
ing Wzc, is designated as PCP-2a (
Morona et al., 2000
). The members of
this group possess an additional carboxy-terminal cytoplasmic domain,
which contains the Walker Box A and B motifs that are found in a vari-
ety of ATP- and GTP-hydrolysing proteins (
Cuthbertson et al., 2010
;
Figure 7.2
General characteristics of the polysaccharide copolymerase (PCP) family
proteins. The members of this family possess two transmembrane regions (TM1 and
TM2) flanking a large periplasmatic loop and a proline- and glycine-rich domain that
precedes and overlaps the TM2 (depicted in grey). PCP-1 proteins participate in the bio-
synthesis of the O-antigen of LPS following the Wzy-dependent pathway. The PCP-2a
are involved in EPS assembly and export in Gram-negative bacteria, also following the
Wzy-dependent pathway. The members of this group possess an additional carboxy-
terminal cytoplasmic domain, containing the Walker Box A and B motifs, a DXD sig-
nature, and a carboxy-terminal tyrosine rich region. PCP-3 proteins participate in the
ABC-dependent EPS assembly and export systems. The PCP-1 and PCP-3 proteins are
smaller than the PCP-2a, lacking the additional carboxy-terminal cytoplasmic region
(
Cuthbertson et al., 2009
;
Morona et al., 2000
,
2009
;
Whitfield, 2010
).
