title: Micelle-to-vesicle transition of an iron-chelating microbial surfactant, marinobactin E.
abstract: Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) techniques have been applied to study the self-assembly processes of a microbially produced siderophore, marinobactin E (ME). ME is one of a series of marinobactins A-E that facilitate Fe(III) acquisition by the source bacterium through coordination of Fe(III) by the marinobactin headgroup. ME is a six-amino-acid peptide amphiphile appended by palmitic acid (C16), and differs only in the nature of the fatty acid moiety from the other marinobactins. Apo-ME (uncoordinated ME) assembles to form micelles with an average diameter of 4.0 nm. Upon coordination of one equivalent of Fe(III), the mean micellar diameter of Fe(III)-ME shrinks to approximately 2.8 nm. However, in the presence of excess Fe(III), Fe(III)-ME undergoes a micelle-to-vesicle transition (MVT). At a small excess of Fe(III) over Fe(III)-ME (i.e., <1.2 Fe(III)/ME), a fraction of the Fe(III)-ME micelles rearrange into approximately 200 nm diameter unilamellar vesicles. At even greater Fe(III)/ME ratios (e.g., 2-3) multilamellar aggregates begin to emerge, consistent with either multilamellar vesicles or lamellar stacks. The MVT exhibited by ME may represent a unique mechanism by which marine bacteria may detect and sequester iron required for growth.
authors.affiliation: Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106-9510, USA.
authors.forename: Tate
authors.initials: T
authors.lastname: Owen
authors.forename: Roger
authors.initials: R
authors.lastname: Pynn
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Martinez
authors.forename: Alison
authors.initials: A
authors.lastname: Butler
mesh_terms: D007502:Iron Chelating Agents / Q000737:chemistry*; D008823:Micelles; D009842:Oligopeptides / Q000737:chemistry*; D010169:Palmitic Acids / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D007502:Iron Chelating Agents; D008823:Micelles; D009842:Oligopeptides; D010169:Palmitic Acids; D013501:Surface-Active Agents; C521124:marinobactin E