A tenth atp gene and the conserved atpI gene of a Bacillus atp operon have a role in Mg ²⁺ uptake

Abstract

The atp operon of alkaliphilic Bacillus pseudofirmus OF4, as in most prokaryotes, contains the eight structural genes for the F-ATPase (ATP synthase), which are preceded by an atpI gene that encodes a membrane protein of unknown function. A tenth gene, atpZ, has been found in this operon, which is upstream of and overlapping with atpI. Most Bacillus species, and some other bacteria, possess atpZ homologues. AtpZ is predicted to be a membrane protein with a hairpin topology, and was detected by Western analyses. Deletion of atpZ, atpI, or atpZI from B. pseudofirmus OF4 led to a requirement for a greatly increased concentration of Mg 2؉ for growth at pH 7.5. Either atpZ, atpI, or atpZI complemented the similar phenotype of a triple mutant of Salmonella typhimurium (MM281), which is deficient in Mg 2؉ uptake. atpZ and atpI, separately and together, increased the Mg 2؉ -sensitive 45 Ca 2؉ uptake by vesicles of an Escherichia coli mutant that is defective in Ca 2؉ and Na ؉ efflux. We hypothesize that AtpZ and AtpI, as homooligomers, and perhaps as heterooligomers, are Mg 2؉ transporter, Ca 2؉ transporter, or channel proteins. Such proteins could provide Mg 2؉ , which is required by ATP synthase, and also support charge compensation, when the enzyme is functioning in the hydrolytic direction; e.g., during cytoplasmic pH regulation. P rokaryotic atp operons encode the cell membrane F-type ATPase (ATP synthase) that couples the energy of an electrochemical H ϩ gradient (or sometimes Na ϩ ), to the synthesis of ATP, from ADP and P i . In the reverse reaction, the ATPase hydrolyzes ATP concomitant with H ϩ (or Na ϩ ) efflux, thereby contributing to cytoplasmic pH regulation and͞or generation of a transmembrane electrochemical gradient under fermentative conditions (1-4). Most atp operons, like that of Escherichia coli, contain the eight structural genes for the ATPase, atpBEFHAGDC, which are preceded by atpI (5). The Escherichia coli atpI is expressed, and its product associates with the membrane, as predicted from its deduced sequence (6-9). Whereas there is no demonstrated effect of AtpI on expression or assembly of the ATPase, an atpI deletion strain of E. coli has been reported to have a reduced growth yield (7). There is no function established for this "mysterious ninth gene" (10) that accounts for such an effect. We report here the finding of another gene, encoding a membrane protein, that is upstream of the atpI gene, and within the atp operon of alkaliphilic Bacillus pseudofirmus OF4. This gene, designated atpZ, was discovered during attempts to introduce site-directed changes in alkaliphilespecific motifs of the membrane-embedded F-ATPase subunits of B. pseudofirmus OF4 (11). A cassette introduced just upstream of the putative atp promoter abolished atp expression. This finding led us to reexamine the location of the atp operon promoter, to the inclusion of atpZ in the extended operon, and then to an exploration of the effects of deleting atpI as well as atpZ. The results suggest a cation translocation function ...

Transcriptional analysis of the F0F1 ATPase operon of Corynebacterium glutamicum ATCC 13032 reveals strong induction by alkaline pH

“…We found a weak expression of the atpI gene in comparison with that of the atpB gene, as occurs in E. coli and Ilyobacter tartaticus (Schneppe et al, 1991;Meier et al, 2003). Poor or null atpI gene expression is a common feature among bacteria (Amaresh & Ljungdahl, 1997;Walker et al, 1984;Hicks et al, 2003). (Frasch, 2000).…”

Roles of AtpI and Two YidC-Type Proteins from Alkaliphilic Bacillus pseudofirmus OF4 in ATP Synthase Assembly and Nonfermentative Growth

“…When atpI, originally called uncI, was first reported (10), it was suggested that it encoded a pilot protein with a role in assembly of the membrane sector of the synthase, although AtpI clearly did not have an essential role, since deletion of the atpI gene from Escherichia coli only slightly reduced the growth yield and ATPase activity (11). Similarly, we recently showed that atpI, as well as the atpZ gene that is found upstream of atpI in many low %GC bacteria, could be deleted from the chromosome of alkaliphilic Bacillus pseudofirmus OF4 without apparent loss of the capacity to grow nonfermentatively (8,12).…”

“…Table 1 lists the bacterial strains and plasmids used. The WT (wild-type) strain is alkaliphilic Bacillus pseudofirmus OF4 811M (12). The ⌬atpZ, ⌬atpI, ⌬atpZI, and ⌬F o strains are from laboratory stocks (12,31).…”

“…The WT (wild-type) strain is alkaliphilic Bacillus pseudofirmus OF4 811M (12). The ⌬atpZ, ⌬atpI, ⌬atpZI, and ⌬F o strains are from laboratory stocks (12,31). In order to facilitate purification of the ATP synthase from ⌬atpZ, ⌬atpI, and ⌬atpZI strains, six histidines were placed in the ␤ subunit of the ATP synthase as described previously (28).…”

“…The bacterial enzyme consists of a soluble F 1 domain (subunits ␣ 3 ␤ 3 ␥␦ε) and a membrane-embedded F o domain (subunits ab 2 c [10][11][12][13][14][15] ) (4)(5)(6). In most bacteria, the atp operon contains nine open reading frames: eight structural genes (atpBEFHAGDC) of ATP synthase preceded by a ninth atpI gene, which encodes a membrane protein and is not a structural gene (7)(8)(9).…”