Subsystem: L-Cystine Uptake and Metabolism

This subsystem's description is:

The symporter YhcL and two ATP binding cassette transporters, YtmJKLMN and YckKJI, were shown to mediate L-cystine uptake in Bacillus subtilis.
====== From Ref.1 :============================
A triple yhcL ytmJKLMN yckK mutant was unable to grow in the presence of L-cystine and to take up L-cystine. We propose that yhcL, ytmJKLMN, and yckKJI should be renamed tcyP, tcyJKLMN, and tcyABC, respectively. The L-cystine uptake by YhcL (Km = 0.6 然) was strongly inhibited by seleno-DL-cystine, while the transport due to the YtmJKLMN system (Km = 2.5 然) also drastically decreased in the presence of DL-cystathionine, L-djenkolic acid, or S-methyl-L-cysteine. Accordingly, a ytmJKLMN mutant did not grow in the presence of 100 然 DL-cystathionine, 100 然 L-djenkolic acid, or 100 然 S-methyl-L-cysteine. The expression of the ytmI operon and the yhcL gene was regulated in response to sulfur availability, while the level of expression of the yckK gene remained low under all the conditions tested.

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In E. coli, two kinetically identifiable cystine transport systems are present; one is shared with diaminopimelic acid and several cystine analogues, and the other is more specific. The first system, which is sensitive to osmotic shock, corresponds to an ABC transporter. The bacterial ABC importers include one or two ATP binding proteins localized to the inner side of the cytoplasmic membrane, one or two transmembrane proteins, and a high-affinity solute binding protein external to the cytoplasmic membrane. The periplasmic cystine binding protein from E. coli has been characterized and was identified as FliY. The fliY gene forms an operon with fliA, which participates in transcription of class III genes involved in flagellar synthesis. FliY is not required for motility, and its possible role in flagellar synthesis remains to be established. The YecS and YecC proteins probably correspond to the E. coli permease and ATP binding protein of a cystine ABC transporter, but this has never been substantiated by experimental data. The yecS and yecC genes are separated from fliY only by the yedO gene encoding a D-cysteine desulfhydrase. It has been proposed that these genes could form an operon .
In gram-positive bacteria, the solute binding protein BspA has been shown to be required for L-cystine uptake in Lactobacillus fermentum.

In Salmonella enterica serovar Typhimurium, L-cystine is taken up by three different systems, CTS-1 (Km = 2 然), CTS-2 (Km = 0.1 然), and CTS-3 (nonsaturable).

==== L-cystine symporter: =============================

Probable L-cystine symporters, which are highly similar to TcyP, are present in Bacillus anthracis, Bacillus cereus, Staphylococcus aureus, Staphylococcus epidermidis, Oceanobacillus iheyensis, and Enterococcus faecalis. A TcyP-like protein is also found in several {gamma}-proteobacteria, including E. coli, Salmonella enterica serovar Typhi, S. enterica serovar Typhimurium, Haemophilus influenzae, Photorhabdus luminescens, Yersinia pestis, Vibrio cholerae, and Pseudomonas putida. Interestingly, the YdjN polypeptide from E. coli, which exhibits 45% identity to TcyP, could correspond to the second uncharacterized L-cystine transporter. The ABC transporter encoded by the ytmI operon is present only in Listeria species (http://genolist.pasteur.fr). The TcyKLMN proteins exhibit 65 to 75% identity with the corresponding Listeria polypeptides. However, a unique solute binding protein is present in Listeria (Lmo2349 or Lin2443) instead of the two proteins present in B. subtilis, TcyJ and TcyK. A TcyABC-like ABC transporter is found in B. anthracis, B. cereus, Bacillus halodurans, S. aureus, S. epidermidis, Clostridium acetobutylicum, Neisseria meningitidis, H. influenzae, and probably several lactobacilli.

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