PTS Lactose-N,N'-Diacetylchitobiose Family explained

The PTS Lactose-N,N’-Diacetylchitobiose (Lac) Family (TC# 4.A.3) includes several sequenced lactose porters of Gram-positive bacteria, as well as the Escherichia coli and Borrelia burgdorferi N,N'-diacetylchitobiose (Chb) porters.^{[1] [2]} It is part of the PTS-GFL superfamily. The former can transport aromatic β-glucosides and cellobiose, as well as Chb. However, only Chb induces expression of the chb operon.

Structure

While the Lac porters consist of two polypeptide chains (IIA and IICB), the Chb porters of E. coli and B. burgdorferi consist of three (IIA, IIB and IIC). In E. coli, the IIA^Chb protein has been shown to form a stable dimer both when phosphorylated and when unphosphorylated. The IIC domains of these permeases are believed to have a uniform topology with 8 TMSs.^[3]

Lac porters in E. coli

In E. coli, the IIB^Chb is a monomer. Two IIB^Chb monomers associate with the IIA^Chb dimer. The structure of the IIB domain of the Chb porter has been determined both by NMR and by X-ray crystallography. It exhibits an α/β doubly wound superfold. This is different from the structure of the IIB^Glc and IIB^Mandomains. IIB^Sgc, believed to function in pentose transport, is homologous to IIB^Lac and IIB^Chb. In Bacillus cereus, the crystal structure of the Chb protein is known.^[4] The IIC domains of members of the Lac family are all more similar to each other than they are to those of the Glc, Bgl, Fru and Mtl families.

Notes and References

1. Keyhani. N. O.. Bacia. K.. Roseman. S.. 2000-10-20. The transport/phosphorylation of N,N'-diacetylchitobiose in Escherichia coli. Characterization of phospho-IIB(Chb) and of a potential transition state analogue in the phosphotransfer reaction between the proteins IIA(Chb) AND IIB(Chb). The Journal of Biological Chemistry. 275. 42. 33102–33109. 10.1074/jbc.M001045200. 0021-9258. 10913119. free.
2. Tilly. K.. Elias. A. F.. Errett. J.. Fischer. E.. Iyer. R.. Schwartz. I.. Bono. J. L.. Rosa. P.. 2001-10-01. Genetics and regulation of chitobiose utilization in Borrelia burgdorferi. Journal of Bacteriology. 183. 19. 5544–5553. 10.1128/JB.183.19.5544-5553.2001. 0021-9193. 95445. 11544216.
3. Nguyen. Thai X.. Yen. Ming-Ren. Barabote. Ravi D.. Saier. Milton H.. 2006-01-01. Topological predictions for integral membrane permeases of the phosphoenolpyruvate:sugar phosphotransferase system. Journal of Molecular Microbiology and Biotechnology. 11. 6. 345–360. 10.1159/000095636. 1464-1801. 17114898. 25965070 .
4. Cao. Yu. Jin. Xiangshu. Levin. Elena J.. Huang. Hua. Zong. Yinong. Quick. Matthias. Weng. Jun. Pan. Yaping. Love. James. 2011-05-05. Crystal structure of a phosphorylation-coupled saccharide transporter. Nature. 473. 7345. 50–54. 10.1038/nature09939. 1476-4687. 3201810. 21471968. 2011Natur.473...50C .