Supplementary material to “Two minimal Tat translocases in Bacillus”
Jan D.H. Jongbloed, Ulrike Grieger, Haike Antelmann, Michael Hecker, Reindert
Nijland, Sierd Bron, and Jan Maarten van Dijl
The YwbN protein
The gene encoding YwbN is organized in an operon-like structure that comprises
three genes: ywbL, ywbM, and ywbN. Interestingly, the presence of these three
genes in an operon-like structure is conserved in the genomes of all bacteria that
contain a ywbN gene (Fig. S1). The YwbL protein is predicted to be an integral
membrane protein with sequence similarity to iron permeases, like the one of
Saccharomyces cerevisiae (Stearmann et al., 1996). Predictions using the TMHMM
algorithm (http://www.cbs.dtu.dk/services/TMHMM-2.0) indicate that YwbL is
composed of an N-terminal membrane anchor, followed by a large cytoplasmic part
and seven C-terminal transmembrane segments. In contrast, YwbM is a predicted
lipoprotein (Tjalsma et al., 1999) with homology to proteins putatively involved in iron
transport (proteins of Actinobacillus pleuropneumoniae serovar, Rhodospirillum
rubrum Pseudomonas syringae, and Pseudomonas fluorescens). The YwbN protein,
which has an RR-signal peptide, shows significant similarity to putative irondependent peroxidases of Burkholderia fungorum, Actinobacillus pleuropneumoniae
serovar, Pseudomonas syringae, Pseudomonas fluorescens, Rhodospirillum rubrum,
and Corynebacterium glutamicum (data not shown; Table S1). These observations
suggest that proteins encoded by the ywbLMN operon are part of a transport system
for metal ions. This idea is strongly supported by the observation that the expression
of this operon is derepressed upon mutation of fur and by treatment of wild-type cells
with the iron chelator 2,2’-dipyridyl (Baichoo et al., 2002). The B. subtilis Fur (ferric
uptake repressor) protein coordinates a global transcriptional response to iron
starvation. Notably, all homologues of YwbN that contain a signal peptide appear to
be exported in a Tat-dependent manner, as judged by the presence of “E. coli
consensus” RR-motifs in their signal peptides (Table S1).