The BCCT-family of carriers: from physiology to crystal structure

Christine Maria Ziegler (1) , Erhard Bremer (2) , Reinhard Krämer (3)

1 Department of Structural Biology [Frankfurt am Main]
2 Department of Biology
3 Institut fur Biochemie

To ensure a physiologically acceptable level of cellular hydration and turgor at high osmolarity, many bacteria accumulate compatible solutes. Osmotically controlled uptake systems allow the scavenging of these compounds from environmental sources as osmoprotectants. Some of these transporters belong to the BCCT family (betaine-choline-carnitine-transporter), sodium- or proton-coupled carriers (e.g. BetP and BetT, respectively) that are ubiquitous in microorganisms. The BCCT family also contains CaiT, a L-carnitine/γ-butyrobetaine antiporter that is not involved in osmotic stress responses. The glycine betaine transporter BetP from Corynebacterium glutamicum is a representative for osmoregulated symporters of the BCCT-family and functions both as an osmosensor and osmoregulator. The crystal structure of BetP in complex with its substrate glycine betaine and two crystal structures of CaiT in complex with L-carnitine and γ-butyrobetaine were reported recently. These structures, and biochemical data on the activity control of BetP in response to osmotic stress enables a correlation between the sensing of osmotic stress by a transporter protein with the ensuing regulation of transport activity. Molecular determinants governing the high-affinity binding of the compatible solutes by BetP and CaiT, the coupling in symporters and antiporters, and the osmoregulatory properties are discussed in detail for BetP and various BCCT carriers.

Mots clés: Life Sciences

Christine Maria Ziegler, Erhard Bremer, Reinhard Krämer. The BCCT-family of carriers: from physiology to crystal structure. Molecular Microbiology, 2010, ⟨10.1111/j.1365-2958.2010.07332.x⟩. ⟨hal-00572623⟩