title: In vitro functional characterization of the Na+/H+ antiporters in Corynebacterium glutamicum.
abstract: Corynebacterium glutamicum, typically used as industrial workhorse for amino acid production, is a moderately salt-alkali-tolerant microorganism with optimal growth at pH 7-9. However, little is known about the mechanisms of salt-alkali tolerance in C. glutamicum. Here, the catalytic capacity of three putative Na(+)/H(+) antiporters from C. glutamicum (designated as Cg-Mrp1, Cg-Mrp2 and Cg-NhaP) were characterized in an antiporter-deficient Escherichia coli KNabc strain. Only Cg-Mrp1 was able to effectively complement the Na(+)-sensitive of E. coli KNabc. Cg-Mrp1 exhibited obvious Na(+)(Li(+))/H(+) antiport activities with low apparent Km values of 1.08 mM and 1.41 mM for Na(+) and Li(+), respectively. The Na(+)/H(+) antiport activity of Cg-Mrp1 was optimal in the alkaline pH range. All three antiporters showed detectable K(+)/H(+) antiport activitiy. Cg-NhaP also exhibited Na(+)(Li(+),Rb(+))/H(+) antiport activities but at lower levels of activity. Interestingly, overexpression of Cg-Mrp2 exhibited clear Na(+)(K(+))/H(+) antiport activities. These results suggest that C. glutamicum Na(+)(K(+))/H(+) antiporters may have overlapping roles in coping with salt-alkali and perhaps high-osmolarity stress.
authors.affiliation: Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, PR China.
authors.forename: Ning
authors.initials: N
authors.lastname: Xu
authors.affiliation: Department of Microbiology and immunology, College of Biological Sciences, China Agricultural University, Beijing 10094, PR China.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, PR China School of Food Engineering and Biotechnology, Tianjin University of Science and Technology, Tianjin 300457, PR China.
authors.forename: Haijiao
authors.initials: H
authors.lastname: Cheng
authors.affiliation: School of Food Engineering and Biotechnology, Tianjin University of Science and Technology, Tianjin 300457, PR China.
authors.forename: Qingdai
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, PR China liu_jun@tib.cas.cn.
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.affiliation: Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, PR China.
authors.forename: Yanhe
authors.initials: Y
authors.lastname: Ma
mesh_terms: D003001:Cloning, Molecular; D048230:Corynebacterium glutamicum / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D005816:Genetic Complementation Test; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: D017923:Sodium-Hydrogen Exchangers
keywords: Corynebactrerium glutamicum; Na+/H+ antiporters; function