The lysine 299 residue endows the multisubunit Mrp1 antiporter with dominant roles in Na+ resistance and pH homeostasis in Corynebacterium glutamicum

Ning Xu, Yingying Zheng, Xiaochen Wang, Terry A. Krulwich, Yanhe Ma, Jun Liu

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14 Scopus citations

Abstract

Corynebacterium glutamicum is generally regarded as a moderately saltand alkali-tolerant industrial organism. However, relatively little is known about the molecular mechanisms underlying these specific adaptations. Here, we found that the Mrp1 antiporter played crucial roles in conferring both environmental Na+ resistance and alkali tolerance whereas the Mrp2 antiporter was necessary in coping with high-KCl stress at alkaline pH. Furthermore, the δmrp1 δmrp2 double mutant showed the most-severe growth retardation and failed to grow under high-salt or alkaline conditions. Consistent with growth properties, the Na+/H+ antiporters of C. glutamicum were differentially expressed in response to specific salt or alkaline stress, and an alkaline stimulus particularly induced transcript levels of the Mrptype antiporters. When the major Mrp1 antiporter was overwhelmed, C. glutamicum might employ alternative coordinate strategies to regulate antiport activities. Site-directed mutagenesis demonstrated that several conserved residues were required for optimal Na+ resistance, such as Mrp1A K299, Mrp1C I76, Mrp1A H230, and Mrp1D E136. Moreover, the chromosomal replacement of lysine 299 in the Mrp1A subunit resulted in a higher intracellular Na+ level and a more alkaline intracellular pH value, thereby causing a remarkable growth attenuation. Homology modeling of the Mrp1 subcomplex suggested two possible ion translocation pathways, and lysine 299 might exert its effect by affecting the stability and flexibility of the cytoplasm-facing channel in the Mrp1A subunit. Overall, these findings will provide new clues to the understanding of salt-alkali adaptation during C. glutamicum stress acclimatization.

Original languageEnglish
Article numbere00110-18
JournalApplied and Environmental Microbiology
Volume84
Issue number10
DOIs
StatePublished - 1 May 2018

Keywords

  • Corynebacterium glutamicum
  • Expression pattern
  • Mrp-type system
  • Na/H antiporter
  • Site mutations

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