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Gramicidin D (gramicidin + d)

Distribution by Scientific Domains

Chemistry	60%

Selected Abstracts

Presence of a Na+ -stimulated P-type ATPase in the plasma membrane of the alkaliphilic halotolerant cyanobacterium Aphanothece halophytica

FEMS MICROBIOLOGY LETTERS, Issue 1 2007
Kanjana Wiangnon
Abstract Aphanothece cells could take up Na+ and this uptake was strongly inhibited by the protonophore, carbonyl cyanide m -chlorophenylhydrazone (CCCP). Cells preloaded with Na+ exhibited Na+ extrusion ability upon energizing with glucose. Na+ was also taken up by the plasma membranes supplied with ATP and the uptake was abolished by gramicidin D, monensin or Na+ -ionophore. Orthovanadate and CCCP strongly inhibited Na+ uptake, whereas N, N, -dicyclohexylcarbodiimide (DCCD) slightly inhibited the uptake. Plasma membranes could hydrolyse ATP in the presence of Na+ but not with K+, Ca2+ and Li+. The Km values for ATP and Na+ were 1.66±0.12 and 25.0±1.8 mM, respectively, whereas the Vmax value was 0.66±0.05 ,mol min,1 mg,1. Mg2+ was required for ATPase activity whose optimal pH was 7.5. The ATPase was insensitive to N -ethylmaleimide, nitrate, thiocyanate, azide and ouabain, but was substantially inhibited by orthovanadate and DCCD. Amiloride, a Na+/H+ antiporter inhibitor, and CCCP showed little or no effect. Gramicidin D and monensin stimulated ATPase activity. All these results suggest the existence of a P-type Na+ -stimulated ATPase in Aphanothece halophytica. Plasma membranes from cells grown under salt stress condition showed higher ATPase activity than those from cells grown under nonstress condition. [source]

The first crystal structure of a gramicidin complex with sodium: high-resolution study of a nonstoichiometric gramicidin D,NaI complex

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2010
A. Olczak
The crystal structure of the nonstoichiometric complex of gramicidin D with NaI has been studied using synchrotron radiation at 100,K. The limiting resolution was 1.25,Å and the R factor was 16% for 19,883 observed reflections. The general architecture of the antiparallel two-stranded gramicidin dimers in the studied crystal was a right-handed antiparallel double-stranded form that closely resembles the structures of other right-handed species published to date. However, there were several surprising observations. In addition to the significantly different composition of linear gramicidins identified in the crystal structure, including the absence of the gramicidin C form, only two cationic sites were found in each of the two independent dimers (channels), which were partially occupied by sodium, compared with the seven sites found in the RbCl complex of gramicidin. The sum of the partial occupancies of Na+ was only 1.26 per two dimers and was confirmed by the similar content of iodine ions (1.21 ions distributed over seven sites), which was easily visible from their anomalous signal. Another surprising observation was the significant asymmetry of the distributions and occupancies of cations in the gramicidin dimers, which was in contrast to those observed in the high-resolution structures of the complexes of heavier alkali metals with gramicidin D, especially that of rubidium. [source]

Membrane Permeabilization of a Mammalian Neuroendocrine Cell Type (PC12) by the Channel-Forming Peptides Zervamicin, Alamethicin, and Gramicidin

CHEMISTRY & BIODIVERSITY, Issue 6 2007

Abstract Zervamicin IIB (ZER) is a 16-mer peptaibol that produces voltage-dependent conductances in artificial membranes, a property considered responsible for its antimicrobial activity to mainly Gram -positive microorganisms. In addition, ZER appears to inhibit the locomotor activity of the mouse (see elsewhere in this Issue), probably by affecting the brain. To examine whether the electrophysiological properties of the neuronal cells of the central neural system might be possibly influenced by the pore forming ZER, the present study was undertaken as a first attempt to unravel the molecular mechanism of this biological activity. To this end, membrane permeabilization of the neuron-like rat pheochromocytoma cell (PC12) by the channel-forming ZER was studied with the whole-cell patch-clamp technique, and compared with the permeabilizations of the well-known voltage-gated peptaibol alamethicin F50/5 (ALA) and the cation channel-forming peptide-antibiotic gramicidin D (GRAM). While 1,,M GRAM addition to PC12 cells kept at a membrane potential Vm=0,mV causes an undelayed gradual increase of a leak conductance with a negative reversal potential of ca. ,24,mV, ZER and ALA are ineffective at that concentration and potential. However, if ZER and ALA are added in 5,10,,M concentrations while Vm is kept at ,60,mV, they cause a sudden and strong permeabilization of the PC12 cell membrane after a delay of 1,2,min, usually leading to disintegrating morphology changes of the patched cell but not of the surrounding cells of the culture at that time scale. The zero reversal potential of the established conductance is consistent with the known aselectivity of the channels formed. This sudden permeabilization does not occur within 10,20,min at Vm=0,mV, in accordance with the known voltage dependency of ZER and ALA channel formation in artificial lipid membranes. The permeabilizing action of these peptaibols on the culture as a whole is further supported by K+ -release measurements from a PC12 suspension with a K+ -selective electrode. Further analysis suggested that the permeabilizing action is associated with extra- or intracellular calcium effects, because barium inhibited the permeabilizing effects of ZER and ALA. We conclude, for the membrane of the mammalian neuron-like PC12 cell, that the permeabilizing effects of the peptides ZER and ALA are different from those of GRAM, consistent with earlier studies of these peptides in other (artificial) membrane systems. They are increased by cis -positive membrane potentials in the physiological range and may include calcium entry into the PC12 cell. [source]