Functional properties of LptA and LptD in Anabaena sp. PCC 7120

Abstract

Lipopolysaccharides (LPS) are central components of the outer membrane and consist of Lipid A, the core polysaccharide, and the O-antigen. The synthesis of LPS is initiated at the cytosolic face of the cytoplasmic membrane. The subsequent transport to and across the outer membrane involves multiple lipopolysaccharide transport (Lpt) proteins. Among those proteins, the periplasmic-localized LptA and the outer membrane-embedded LptD participate in the last steps of transfer and insertion of LPS into the outer membrane. While the process is described for proteobacterial model systems, not much is known about the machinery in cyanobacteria. We demonstrate that anaLptD (alr1278) of Anabaena sp. PCC 7120 is important for cell wall function and its pore domain shows a Lipid A sensitive cation-selective gating behavior. The N-terminal domain of anaLptD recognizes anaLptA (alr4067), but not ecLptA. Furthermore, anaLptA specifically interacts with the Lipid A from Anabaena sp. PCC 7120 only, while anaLptD binds to Lipid A isolated from Escherichia coli as well. Based on the comparative analysis of proteins from E. coli and Anabaena sp. we discuss the properties of the cyanobacterial Lpt system.

The plastid outer membrane localized LPTD1 is important for glycerolipid remodelling under phosphate starvation

“…3e). We observed one uniform open state with a conductance of 200 ± 20 pS, which is smaller than found for the pore of anaLptD (520 pS; Haarmann et al 2010;Hsueh et al 2015). Based on the conductance, we calculated the pore diameter (Hille 2001;Hinnah et al 2002) to about 9 Å and a pore area of about 60 Å 2 assuming a circular pore, 4-fold smaller than the area of the pore of anaLptD transporting Lipid A (Haarmann et al 2010).…”

“…The rectifying behaviour and the cation selective nature were also observed for the full length and the entire pore forming region of anaLptD, the LptD ortholog in Anabaena sp. PCC 7120 (Haarmann et al ; Hsueh et al ) and suggests that the flow of ions through the channel occurs preferentially in one direction.…”

“…Asterisks indicate digestion products. Hsueh et al 2015) and suggests that the flow of ions through the channel occurs preferentially in one direction. Next, we determined the conductivity of the atLPTD1 channel in 250 mM KCl (Fig.…”

Comparative Phenotypic Analysis of Anabaena sp. PCC 7120 Mutants of Porinlike Genes

“…2B, first and second panel). This behavior was not described before [45,46,59] as the effect was only visible when the culture was sufficiently diluted (Fig. 2B, second panel).…”

“…In addition, mutants exhibiting alterations in outer membrane integrity, bearing either an insertion in Anabaena sp. omp85 genes (AFS-I- alr0075 , AFS-I- alr2269 and AFS-I- alr4893 ; AFS stands for A nabaena mutant created in F rankfurt by the S chleiff group)[ 58 ] or the tic22 gene (AFS-I- tic22 , alr0114 , [ 45 , 46 , 59 ]) were used as additional controls. As reported before, AFS-I- alr0075 , AFS-I- alr2269 and AFS-I- alr4893 could not be segregated since wild-type copies could be amplified even after exposing the strains to increased concentrations of antibiotics [ 58 ] ( Fig.…”