title: Membrane dynamics of the amphiphilic siderophore, acinetoferrin.
abstract: Acinetobacter haemolyticus is an antibiotic resistant, pathogenic bacterium responsible for an increasing number of hospital infections. Acinetoferrin (Af), the amphiphilic siderophore isolated from this organism, contains two unusual trans-2-octenoyl hydrocarbon chains reminiscent of a phospholipid structural motif. Here, we have investigated the membrane affinity of Af and its iron complex, Fe-Af, using small and large unilamellar phospholipid vesicles (SUV and LUV) as model membranes. Af shows a high membrane affinity with a partition coefficient, K(x)= 6.8 x 10(5). Membrane partitioning and trans-membrane flip-flop of Fe-Af have also been studied via fluorescence quenching of specifically labeled vesicle leaflets and (1)H NMR line-broadening techniques. Fe-Af is found to rapidly redistribute between lipid and aqueous phases with dissociation/partitioning rates of k(off) = 29 s(-1) and k(on) = 2.4 x 10(4) M(-1) s(-1), respectively. Upon binding iron, the membrane affinity of Af is reduced 30-fold to K'(x) = 2.2 x 10(4) for Fe-Af. In addition, trans-membrane flip-flop of Fe-Af occurs with a rate constant, k(p) = 1.2 x 10(-3) s(-1), with egg-PC LUV and a half-life time around 10 min with DMPC SUV. These properties are due to the phospholipid-like conformation of Af and the more extended conformation of Fe-Af that is enforced by iron binding. Remarkable similarities and differences between Af and another amphiphilic siderophore, marinobactin E, are discussed. The potential biological implications of Af and Fe-Af are also addressed. Our approaches using inner- and outer-leaflet-labeled fluorescent vesicles and (1)H NMR line-broadening techniques to discern Af-mediated membrane partitioning and trans-membrane diffusion are amenable to similar studies for other paramagnetic amphiphiles.
authors.affiliation: Department of Chemistry, Princeton University, Princeton, NJ 08540, USA.
authors.forename: Minkui
authors.initials: M
authors.lastname: Luo
authors.forename: Evgeny A
authors.initials: EA
authors.lastname: Fadeev
authors.forename: John T
authors.initials: JT
authors.lastname: Groves
mesh_terms: D000150:Acinetobacter / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002951:Citrates / Q000737:chemistry* / Q000378:metabolism; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D006877:Hydroxamic Acids / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D008567:Membranes, Artificial; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010713:Phosphatidylcholines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism; D017262:Siderophores / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002951:Citrates; D005290:Ferric Compounds; D006877:Hydroxamic Acids; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D010743:Phospholipids; D017262:Siderophores; C086668:acinetoferrin; C025314:ferric citrate; D004134:Dimyristoylphosphatidylcholine