PMID:21873238

Citation	Doughty, DM, Coleman, ML, Hunter, RC, Sessions, AL, Summons, RE and Newman, DK (2011) The RND-family transporter, HpnN, is required for hopanoid localization to the outer membrane of Rhodopseudomonas palustris TIE-1. Proc. Natl. Acad. Sci. U.S.A. 108:E1045-51
Abstract	Rhodopseudomonas palustris TIE-1 is a gram-negative bacterium that produces structurally diverse hopanoid lipids that are similar to eukaryotic steroids. Its genome encodes several homologues to proteins involved in eukaryotic steroid trafficking. In this study, we explored the possibility that two of these proteins are involved in intracellular hopanoid transport. R. palustris has a sophisticated membrane system comprising outer, cytoplasmic, and inner cytoplasmic membranes. It also divides asymmetrically, producing a mother and swarmer cell. We deleted genes encoding two putative hopanoid transporters that belong to the resistance-nodulation-cell division superfamily. Phenotypic analyses revealed that one of these putative transporters (HpnN) is essential for the movement of hopanoids from the cytoplasmic to the outer membrane, whereas the other (Rpal_4267) plays a minor role. C(30) hopanoids, such as diploptene, are evenly distributed between mother and swarmer cells, whereas hpnN is required for the C(35) hopanoid, bacteriohopanetetrol, to remain localized to the mother cell type. Mutant cells lacking HpnN grow like the WT at 30 °C but slower at 38 °C. Following cell division at 38 °C, the ΔhpnN cells remain connected by their cell wall, forming long filaments. This phenotype may be attributed to hopanoid mislocalization because a double mutant deficient in both hopanoid biosynthesis and transport does not form filaments. However, the lack of hopanoids severely compromises cell growth at higher temperatures more generally. Because hopanoid mutants only manifest a strong phenotype under certain conditions, R. palustris is an attractive model organism in which to study their transport and function.
Links	PubMed PMC3215060 Online version:10.1073/pnas.1104209108
Keywords	Bacterial Outer Membrane Proteins/physiology; Cell Cycle; Culture Media; Membrane Transport Proteins/physiology; Phylogeny; Protein Transport; Rhodopseudomonas/metabolism; Temperature
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
RHOPT:B3QHB6		GO:0009279: cell outer membrane	ECO:0000315:		C		Encodes for essential proteins involved in intracellular hopanoid transport from the cytoplasmic to the outer membrane. Figure 4 shows the content of lipid extract from membrane fractions from R. palustris compared to the lipid extract from membranes of the mutant strain (Rpal_4254) where the gene was deleted. The WT contained 12.5 +/- 1 ug x mg total lipid extract (TLE); the mutant strain (Rpal_4254) no longer contained hopanoids in the outer membrane. Both WT and Rpal_4254 showed hopanoid content in the whole cell.	complete CACAO 7681
RHOPT:B3QHB6	part_of	GO:0009279: cell outer membrane	ECO:0000315: mutant phenotype evidence used in manual assertion		C		Seeded From UniProt	complete

References

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