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Inhibition of cell growth by an elevated turnover number of melibiose/Na+ symport catalyzed by melibiose permease of Salmonella typhimurium
Author(s) -
Jakkula S. Vivek,
Hodkoff Alexey A.,
Guan Lan
Publication year - 2012
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.26.1_supplement.lb211
Subject(s) - melibiose , symporter , permease , mutant , biochemistry , chemistry , transporter , maltose , enzyme , gene
Melibiose permease of Salmonella typhimurium (MelB St ) catalyzes melibiose/cation (H + , Na + or Li + ) symport. The transport mechanism is still poorly understood. Threading model indicates that a conserved Gly117 (helix IV) is part of the Na + ‐binding site. Recently, mutation analyses suggested that Gly117 plays an important role in cation binding and translocation in MelB St . In this study, we observed that Gly117→Cys MelB St mutant drastically inhibited cell growth in the presence of melibiose in a concentration‐dependent fashion. The mutant G117C increased V max value for melibiose transport by >3 fold with little changes in K m and protein expression. A spontaneous mutation Pro148→Leu was isolated from mutant G117C. Strikingly, the double mutant G117C/P148L grew at a similar rate in the absence or presence of melibiose and also largely decreased the V max value, with 2‐fold lower than obtained from WT. A good correlation between the V max values and the cell‐growth rates in the presence of melibiose indicates that the Na + /melibiose symport dissipates cell membrane potential. With a largely elevated turnover number of melibiose transport, it is likely that the cotransported Na + may collapse the membrane potential and inhibit cell growth. This work was supported by Texas Norman Hackerman Advanced Research Program 010674‐0034‐2009 to LG.