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.

Citric Acid

“…For example, a siderophore named schizokinen has R = H, and n = 2 [558, 559, 561, 564, 566, 568, 572, 574, 577, 579, 580, 595, 596]; awaitin B has n = 3, and anthrobactin has n = 4 [564,596]. If R is carboxylic group COOH, then awaitin A has n = 3 and aerobactin is with n = 4 [557,565,574,579,580,596].…”

“…If one of the N(OH) groups of schizokinen is replaced by NH-group then deoxyschizokinen is formed [568]. Carboxylate type siderophore (two citrate skeleton groups) named rhizoferrin posseses the structure ABA which includes two symmetrical amides A = HOOCCH 2 (OH)C(COOH)CH2CONHCH 2 which are separated by four methylene groups, B = (CH 2 ) 4 [578, 581,592,[596][597][598][599][600].…”

“…Aerobactin and nannochelins have B 1 AB 2 structure where A = HNCOCH 2 (OH)C(COOH)CH 2 CONH, B 1 and B 2 denote different ester groups B 1 = R 1 OCO(CH 2 ) 4 NOHCOR and B 2 = R 2 OCO(CH 2 ) 4 NOHCOR [573, 589,591,593,596]. They are named aerobactin if R 1 = R 2 = R = H; nannochelin C if R = -CHCHC 6 H 5 , R 1 = R 2 = H; nannochelin A if R 1 = R 2 = CH 3 and nannochelin B if R 1 = H, R 2 = CH 3 .…”

“…They are named aerobactin if R 1 = R 2 = R = H; nannochelin C if R = -CHCHC 6 H 5 , R 1 = R 2 = H; nannochelin A if R 1 = R 2 = CH 3 and nannochelin B if R 1 = H, R 2 = CH 3 . Similar structure have various petrabactins, but with a longer chain including more amino groups and different final complex R segments, in the form of differently substituted 2,3-dihydroxybenzenes [579,583,589,594,596,601]. There is also a number of amino analogs of citric acid siderophores [572].…”

Characterization and Fungal Inhibition Activity of Siderophore from Wheat Rhizosphere Associated Acinetobacter calcoaceticus Strain HIRFA32

“…synthesis is intensely studied till date only in clinical strains of A. baumannii and A. haemolyticus. These clinical strains of Acinetobacter are known to produce two siderophores; namely acinetobactin and acinetoferrin, which have been characterized from A. baumannii and A. haemolyticus, respectively [20][21][22]. Thus, the objective of this investigation was to purify and perform structural characterization of siderophore from a strain of A. calcoaceticus previously isolated from rhizosphere of wheat.…”