Doughty, David M. and Coleman, Maureen L. and Hunter, Ryan C. and Sessions, Alex L. and Summons, Roger E. and Newman, Dianne K. (2011) The RND-family transporter, HpnN, is required for hopanoid localization to the outer membrane of Rhodopseudomonas palustris TIE-1. Proceedings of the National Academy of Sciences of the United States of America, 108 (45). E1045-E1051. ISSN 0027-8424 http://resolver.caltech.edu/CaltechAUTHORS:20111128-101611198
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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. C30 hopanoids, such as diploptene, are evenly distributed between mother and swarmer cells, whereas hpnN is required for the C35 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.
|Additional Information:||© 2011 National Academy of Sciences. Edited by Thomas J. Silhavy, Princeton University, Princeton, NJ, and approved July 25, 2011 (received for review March 21, 2011). Published online before print August 22, 2011. The authors thank Dr. Arpita Bose for assistance with molecular techniques, Dr. Julie Maresca for help with phylogenetic profiling, Carolyn Colonero for technical assistance with the GC-MS analyses, and the anonymous reviewers for constructive feedback that improved our manuscript. This work was supported by the Howard Hughes Medical Institute (HHMI) and grants from the NASA exobiology program (to D.K.N. and R.E.S.). D.K.N. is an HHMI Investigator. R.E.S. is supported by the National Science Foundation Chemical Oceanography Program. Author contributions: D.M.D., M.L.C., and D.K.N. designed research; D.M.D., M.L.C., and R.C.H. performed research; A.L.S. and R.E.S. contributed new reagents/analytic tools; D.M.D., M.L.C., A.L.S., R.E.S., and D.K.N. analyzed data; and D.M.D., M.L.C., and D.K.N. wrote the paper. The authors declare no conflict of interest.|
|Subject Keywords:||bacteria; resistance–nodulation–cell division transporters; hopanols; microbial cell biology|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||28 Nov 2011 21:05|
|Last Modified:||28 Nov 2011 21:05|
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