Journal Article

Genetic evidence for functional diversification of gram-negative intermembrane phospholipid transporters

Rai, Ashutosh K., Bennett, Haley C., Kozlova, Anastasiia, Bogdanov, Mikhail, Sawasato, Katsuhiro, Sparagna, Genevieve C., Mitchell, Angela M.

2024

Overview

The outer membrane of gram-negative bacteria is a barrier to chemical and physical stress. Phospholipid transport between the inner and outer membranes has been an area of intense investigation and, in E . coli K-12, it has recently been shown to be mediated by YhdP, TamB, and YdbH, which are suggested to provide hydrophobic channels for phospholipid diffusion, with YhdP and TamB playing the major roles. However, YhdP and TamB have different phenotypes suggesting distinct functions. It remains unclear whether these functions are related to phospholipid metabolism. We investigated a synthetic cold sensitivity caused by deletion of fadR , a transcriptional regulator controlling fatty acid degradation and unsaturated fatty acid production, and yhdP , but not by Δ tamB Δ fadR or Δ ydbH Δ fadR . Deletion of tamB recuses the Δ yhdP Δ fadR cold sensitivity further demonstrating the phenotype is related to functional diversification between these genes. The Δ yhdP Δ fadR strain shows a greater increase in cardiolipin upon transfer to the non-permissive temperature and genetically lowering cardiolipin levels can suppress cold sensitivity. These data also reveal a qualitative difference between cardiolipin synthases in E . coli , as deletion of clsA and clsC suppresses cold sensitivity but deletion of clsB does not. Moreover, increased fatty acid saturation is necessary for cold sensitivity and lowering this level genetically or through supplementation of oleic acid suppresses the cold sensitivity of the Δ yhdP Δ fadR strain. Together, our data clearly demonstrate that the diversification of function between YhdP and TamB is related to phospholipid metabolism. Although indirect regulatory effects are possible, we favor the parsimonious hypothesis that YhdP and TamB have differential phospholipid-substrate transport preferences. Thus, our data provide a potential mechanism for independent control of the phospholipid composition of the inner and outer membranes in response to changing conditions based on regulation of abundance or activity of YhdP and TamB.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Acid production / Biological Transport - genetics / Biology and Life Sciences / Biosynthesis / Cardiolipin / Cardiolipins - genetics / Cardiolipins - metabolism / Carrier proteins / Cell membranes / Cold / Cold Temperature / Diversification / Escherichia coli / Escherichia coli - genetics / Escherichia coli - metabolism / Escherichia coli K12 - genetics / Escherichia coli K12 - metabolism / Escherichia coli Proteins - genetics / Escherichia coli Proteins - metabolism / Ethylenediaminetetraacetic acid / Fatty acids / Fatty Acids - metabolism / Gene deletion / Gene Expression Regulation, Bacterial / Genetic aspects / Genetic diversity / Gram-negative bacteria / Homeostasis / Hydrophobicity / Kinases / Lipid metabolism / Lipids / Membrane Transport Proteins - genetics / Membrane Transport Proteins - metabolism / Monounsaturated fatty acids / Oleic acid / Outer membranes / Phenotypes / Phospholipid composition / Phospholipid Transfer Proteins - genetics / Phospholipid Transfer Proteins - metabolism / Phospholipids / Phospholipids - genetics / Phospholipids - metabolism / Physical Sciences / Physiological aspects / Proteins / Research and Analysis Methods / Temperature preferences