Membrane affinity of the amphiphilic marinobactin siderophores.

TitleMembrane affinity of the amphiphilic marinobactin siderophores.
Publication TypeJournal Article
Year of Publication2002
AuthorsXu G, Martinez JS, Groves JT, Butler A
JournalJ Am Chem Soc
Date Published2002 Nov 13
KeywordsCell Membrane, Chromatography, High Pressure Liquid, Dimyristoylphosphatidylcholine, Ferric Compounds, Halomonas, Kinetics, Membranes, Artificial, Nuclear Magnetic Resonance, Biomolecular, Siderophores, Spectrophotometry, Ultraviolet, Thermodynamics, Ultracentrifugation

Marinobactins are a class of newly discovered marine bacterial siderophores with a unique amphiphilic structure, suggesting that their functions relate to interactions with cell membranes. Here we use small and large unilamellar L-alpha-dimyristoylphosphatidylcholine vesicles (SUVs and LUVs) as model membranes to examine the thermodynamics and kinetics of the membrane binding of marinobactins, particularly marinobactin E (apo-M(E)) and its iron(III) complex, Fe-M(E). Siderophore-membrane interactions are characterized by NMR line broadening, stopped-flow spectrophotometry, fluorescence quenching, and ultracentrifugation. It is determined that apo-M(E) has a strong affinity for lipid membranes with molar fraction partition coefficients K(x)()(apo)(-)(M)E = 6.3 x 10(5) for SUVs and 3.6 x 10(5) for LUVs. This membrane association is shown to cause only a 2-fold decrease in the rate of iron(III) binding by apo-M(E). However, upon the formation of the iron(III) complex Fe-M(E), the membrane affinity of the siderophore decreased substantially (K(x)()(Fe)(-)(M)E = 1.3 x 10(4) for SUVs and 9.6 x 10(3) for LUVs). The kinetics of membrane binding and dissociation by Fe-M(E) were also determined (k(on)(Fe)(-)(M)E = 1.01 M(-)(1) s(-)(1); k(off)(Fe)(-)(M)E = 4.4 x 10(-)(3) s(-)(1)). The suite of marinobactins with different fatty acid chain lengths and degrees of chain unsaturation showed a range of membrane affinities (5.8 x 10(3) to 36 M(-)(1)). The affinity that marinobactins exhibit for membranes and the changes observed upon iron binding could provide unique biological advantages in a receptor-assisted iron acquisition process in which loss of the iron-free siderophore by diffusion is limited by the strong association with the lipid phase.

Alternate JournalJ. Am. Chem. Soc.
PubMed ID12418892
Grant ListGM38130 / GM / NIGMS NIH HHS / United States