Isolation, characterization, and expression of the Corynebacterium glutamicum betP gene, encoding the transport system for the compatible solute glycine betaine

Abstract

Corynebacterium glutamicum accumulates glycine betaine under conditions of high osmolarity. Previous work revealed the existence of a high-affinity glycine betaine permease which is osmotically regulated. In the present study, the corresponding gene was cloned. The betP gene, encoding the glycine betaine uptake carrier, was isolated by heterologous complementation of mutant strain Escherichia coli MKH13. From sequence analysis it is predicted to encode a protein of 595 amino acids. This protein shares 36% identity with the choline transport system BetT and 28% identity with the carnitine transport system CaiT of E. coli, as well as 38% identity with a protein with an unknown function from Haemophilus influenzae. Analysis of hydropathy indicated a common structure for all four transport proteins. After heterologous expression of betP in E. coli MKH13, the measured K m values for glycine betaine and the cotransported Na ؉ were similar to those found in C. glutamicum, whereas the modulation of activity by osmotic gradients was shifted to lower osmotic values.

CaiT of Escherichia coli, a New Transporter Catalyzing l-Carnitine/γ-Butyrobetaine Exchange

“…In contrast to the proposed function of CaiT, all other known members of the BCCT family are proposed to catalyze H ϩ (Na ϩ )/solute symport processes (19,20). 2 However, as more and more primary structures of transporters become available, it appears impossible to infer information on the mechanism of energy coupling from sequence comparisons.…”

“…Some of these transporters have been shown to utilize electrochemical ion gradients (H ϩ , Na ϩ ) for substrate accumulation. In addition, some members of the family are osmotically regulated and share hydrophilic extensions at the N and/or C termini (19,20,22,23).…”

“…1). CaiT displays similarity to the glycine betaine uptake system OpuD from Bacillus subtilis, the choline transporter BetT from E. coli, BetP from Corynebacterium glutamicum, and a BetT-like protein from Haemophilus influenza (19,20). They form a small family of transporters, the betaine/carnitine/ choline transporter (BCCT) 1 family (Transport Protein Database TC 2.A.15).…”

Efflux of Compatible Solutes in Corynebacterium Glutamicum Mediated by Osmoregulated Channel Activity

“…Extremely effective uptake systems for glycine betaine (Farwick et al, 1995;Peter et al, 1996) and proline (Peter, H. and Burkovski, A,, unpublished results) in C. glutumicum and closely related organisms (Bernard et al, 1993;Jebbar et al, 1995) have been observed. These systems are able to accumulate compatible solutes to concentrations higher than 1 M in the cytoplasm (Frings et al, 1993), and are able to maintain extraordinarily high steady-state Concentration gradients of more than IOh-fold (Farwick at al., 1995).…”

“…Extremely effective uptake systems for glycine betaine (Farwick et al, 1995;Peter et al, 1996) 1 M in the cytoplasm (Frings et al, 1993), and are able to maintain extraordinarily high steady-state Concentration gradients of more than IOh-fold (Farwick at al., 1995). It is obvious that C. glutnmicurn needs appropriate efflux systems, too, in order to rapidly release these compounds in case of emergency, i.e.…”