The Kdp-ATPase system and its regulation

Abstract

K+, the dominant intracellular cation, is required for various physiological processes like turgor homeostasis, pH regulation etc. Bacterial cells have evolved many diverse K+ transporters to maintain the desired concentration of internal K+. In E.coli, the KdpATPase (comprising of the KdpFABC complex), encoded by the kdpFABC operon, is an inducible high-affinity K+ transporter that is synthesised under conditions of severe K+ limitation or osmotic upshift. The E.coli kdp expression is transcriptionally regulated by the KdpD and KdpE proteins, which together constitute a typical bacterial two-component signal transduction system. The Kdp system is widely dispersed among the different classes of bacteria including the cyanobacteria. The ordering of the kdpA, kdpB and kdpC is relatively fixed but the kdpD/E genes show different arrangements in distantly related bacteria. Our studies have shown that the cyanobacterium Anabaena sp. strain L-31 possesses two kdp operons, kdp1 and kdp2, of which, the later is expressed under K+ deficiency and desiccation. Among the regulatory genes,the kdpD ORF of Anabaena L-31 is truncated when compared to the kdpD of other bacteria, while a kdpE -like gene is absent. The extremely radio-resistant bacterium, Deinococcus radiodurans strain R1, also shows the presence of a naturally short kdpD ORF similar to Anabaena in its kdp operon. The review elaborates the expression of bacterial kdp operons in response to various environmental stress conditions, with special emphasis on Anabaena. The possible mechanism(s)of regulation of the unique kdp operons from Anabaena and Deinococcus are also discussed.

Experimental design and environmental parameters affect Rhodospirillum rubrum S1H response to space flight

“…The MESSAGE 2 transcriptomic results suggest a response to what is felt by the cell as possibly an osmotic stress. Indeed, together with the gene coding for the biosynthesis of the osmoprotectant trehalose synthesis, two membrane-based osmosensors, the mechanosensitive channel MscS and, to a lesser extent, the two-component sensor kinase KdpD as well as a potassium efflux protein were differentially expressed in the MESSAGE 2 space samples (Wood, 1999;Ballal et al, 2007;Gunasekera et al, 2008;Hurst et al, 2008). During a hypo-osmotic shock, that is, sudden reduction of the external osmolarity, induction of a mechanosensitive channel could act as an emergency safety valve (reviewed in Booth et al, 2007) and decreasing potassium influx (down-regulation Kdp-system) and increasing potassium efflux would help to adapt to this hypo-osmotic conditions.…”

The Staphylococcus aureus KdpDE Two-Component System Couples Extracellular K + Sensing and Agr Signaling to Infection Programming

“…The KdpDE two-component system was first characterized in Escherichia coli, in which proteins KdpD and KdpE regulate the production of the high-affinity K ϩ transporter KdpATPase (6,19,38,40). In E. coli, Kdp-ATPase is an efficient K ϩ -scavenging system that is expressed when cells are subjected to extreme K ϩ limitation or osmotic upshock and other low-affinity K ϩ transporters cannot meet the cellular requirements for K ϩ (2,4,18,26,27,29).…”

“…A BLAST search of Kdp protein sequences shows that the Kdp-ATPase system is widely distributed among Gram-negative bacteria (e.g., E. coli, Salmonella enterica serovar Typhimurium LT2, and Clostridium acetobutylicum) and Gram-positive bacteria (e.g., Bacillus cereus E33L, Alicyclobacillus acidocaldarius, and Mycobacterium tuberculosis). In distantly related bacteria, the ordering of the kdpA, kdpB, and kdpC genes is relatively fixed, but the kdpDE genes show different arrangements (6,44,52). In S. aureus, the organization of the kdpFABC operon is similar to that of E. coli, but the kdpDE genes are arranged in a reverse orientation upstream of the kdpA gene.…”

Genomic composition and dynamics amongMethanomicrobialespredict adaptation to contrasting environments

“…The two sets in M. boonei and one set of Kdp operons in M. palustris likely allow both organisms to overcome low K + concentrations present in oligotrophic and minerotrophic peats. Kdp has a high affinity for K + (K m = 2 μM in Escherichia coli K-12, with 37-63% protein identity to Kdp subunits of M. boonei and M. palustris) and has been shown to concentrate K + in the cytoplasm when extracellular concentrations were as low as 50 nM (Ballal et al, 2007). Our analyses of gene flow dynamics indicated that Kdp was likely acquired subsequent to the divergence of the Methanoregulaceae family, in which the presence of Kdp operons in two peat-dwelling strains, M. boonei and M. palustris, and its absence in two bioreactor-dwelling ones, Methanoregula formicica and M. tarda, suggest that peatlands likely favor methanogens that acquired Kdp.…”