Crosstalk between DnaA Protein, the Initiator of Escherichia coli Chromosomal Replication, and Acidic Phospholipids Present in Bacterial Membranes

Abstract

Anionic (i.e., acidic) phospholipids such as phosphotidylglycerol (PG) and cardiolipin (CL), participate in several cellular functions. Here we review intriguing in vitro and in vivo evidence that suggest emergent roles for acidic phospholipids in regulating DnaA protein-mediated initiation of Escherichia coli chromosomal replication. In vitro acidic phospholipids in a fluid bilayer promote the conversion of inactive ADP-DnaA to replicatively proficient ATP-DnaA, yet both PG and CL also can inhibit the DNA-binding activity of DnaA protein. We discuss how cellular acidic phospholipids may positively and negatively influence the initiation activity of DnaA protein to help assure chromosomal replication occurs once, but only once, per cell-cycle. Fluorescence microscopy has revealed that PG and CL exist in domains located at the cell poles and mid-cell, and several studies link membrane curvature with sub-cellular localization of various integral and peripheral membrane proteins. E. coli DnaA itself is found at the cell membrane and forms helical structures along the longitudinal axis of the cell. We propose that there is cross-talk between acidic phospholipids in the bacterial membrane and DnaA protein as a means to help control the spatial and temporal regulation of chromosomal replication in bacteria.

The Caulobacter crescentus Homolog of DnaA (HdaA) Also Regulates the Proteolysis of the Replication Initiator Protein DnaA

“…At present we have two hypotheses for this apparent paradox. Our first hypothesis is based on observations that new E. coli DnaA synthesis is required for oriC replication (20,45). Newly synthesized apoDnaA protein binds the more abundant ATP nucleotide, and this simple mechanism preferentially produces the active DnaA-ATP.…”

The Arg Fingers of Key DnaA Protomers Are Oriented Inward within the Replication Origin oriC and Stimulate DnaA Subcomplexes in the Initiation Complex

“…This binding produces a highly ordered complex (i.e. an initiation complex) that stimulates local duplex unwinding (2)(3)(4)(5)(6)(7). DnaB helicase is loaded onto the resultant single-stranded DNA via interaction with DnaA and DnaC helicase loader (3).…”

“…The loaded DnaB triggers the formation of the sister replisomes needed for bidirectional DNA synthesis (8). ATP-DnaA is converted to ADP-DnaA, which is inactive for initiation, during replication (2,7,9,10).…”

Negatively Charged Lipids as a Potential Target for New Amphiphilic Aminoglycoside Antibiotics

“…Cardiolipin (CL) 4 is a lipid located primarily in the inner membrane of Gram-negative bacteria like Pseudomonas aeruginosa or Escherichia coli (8,9). In some bacteria like Salmonella, this lipid has also been found in the outer membrane (10,11).…”

“…These distinct assemblies of proteins and/or lipids (3) are related to the regulation of many core processes, such as chromosomal and cell division-related events (4,5). Membrane curvature is potentially responsible for preferential lipid self-assembly behaviors as well as osmosensing (6) and folding of membrane proteins (7).…”