Biology Reference
In-Depth Information
genomics, transcriptomics and proteomics studies that will help clarify the
evolutionary history of EPS assembly and export machinery in cyanobac-
teria.
3.1.1. Reconstruction of the PCP evolutionary history in cyanobacteria
The members of the PCP protein family are characterized by having two
transmembrane regions (TM1 and TM2, respectively) and the presence of a
proline- and glycine-rich domain preceding and overlapping theTM2 (
Cuth-
bertson et al., 2009
;
Morona et al., 2009
). These features were consistently
observed for the putative PCP identified in cyanobacteria (
Table 7.3
). Nev-
ertheless, some of the selected unicellular cyanobacteria lacked an identifiable
pcp
homologue. Blast searches using
wzc
from
E. coli
group 1 capsule (K30)
as query lead to the identification of three putative PCP in
Cyanothece
sp.
PCC 0110 and
Thermosynechococcus elongatus
BP-1, and one putative PCP in
Synechococcus elongatus
PCC 6301 and
Cyanobacterium
UCYN-A. The analysis
of the putative PCP proteins revealed that CY0110_05934, Cyan7822_0908,
syc1292_d, tlr0963 and UCYN_07970 are considerably smaller, lacking the
typical characteristics of PCP proteins. In addition, they are phylogeneti-
cally distant from all other cyanobacterial PCP proteins (
Fig. 7.5
, grey areas).
Therefore, despite the sequence similarity shared with the Gram-negative
PCP proteins, they are considerably different from their cyanobacterial coun-
terparts, and therefore are likely to be involved in different cellular processes.
Consequently, they were not considered for posterior analyses.
On the other hand, several other identified proteins are predicted to
have additional transmembrane domains. These proteins appear intermixed
with the other PCP homologues in bootstrapped-supported clusters, and
thus are likely to be PCP homologues. In general, the cyanobacterial PCP
show the typical features of the PCP-2a group, including the additional
C-terminal region containing the Walker A and B domains, and the DxD
motif commonly found in bacterial tyrosine kinases (
Soulat et al., 2007
).
Nevertheless, some present minor deviations from the canonical sequences
of these motifs, as was previously observed for other bacteria (
Cuthbertson
et al., 2009
). Furthermore, the majority also possesses one or more C-ter-
minal tyrosine residues.
The phylogenetic analysis of the cyanobacterial PCP proteins revealed the
presence of 17 monophyletic clusters (1-17) and two larger bootstrapped-sup-
ported clusters (I and II). Most of the cyanobacterial sequences were grouped
separately from the PCP proteins belonging to other bacteria, suggesting that
after the early separation of the cyanobacterial branch, the genes encoding
