| Novel Lipid Transfer Property of Two Mitochondrial Proteins that Bridge the Inner and Outer Membranes Biophysical Journal, Volume 92, Issue 1, 1 January 2007, Pages 126-137 Raquel F. Epand, Uwe Schlattner, Theo Wallimann, Marie-Lise Lacombe and Richard M. Epand Abstract This study provides evidence of a novel function for mitochondrial creatine kinase (MtCK) and nucleoside diphosphate kinase (NDPK-D). Both are basic peripheral membrane proteins with symmetrical homo-oligomeric structure, which in the case of MtCK was already shown to allow crossbridging of lipid bilayers. Here, different lipid dilution assays clearly demonstrate that both kinases also facilitate lipid transfer from one bilayer to another. Lipid transfer occurs between liposomes mimicking the lipid composition of mitochondrial contact sites, containing 30mol % cardiolipin, but transfer does not occur when cardiolipin is replaced by phosphatidylglycerol. Ubiquitous MtCK, but not NDPK-D, shows some specificity in the nature of the lipids transferred and it is not active with phosphatidylcholine alone. MtCK can undergo reversible oligomerization between dimeric and octameric forms, but only the octamer can bridge membranes and promote lipid transfer. Cytochrome , another basic mitochondrial protein known to bind to anionic membranes but not crosslinking them, is also incapable of promoting lipid transfer. The lipid transfer process does not involve vesicle fusion or loss of the internal contents of the liposomes. Abstract | Full Text | PDF (418 kb) |
| Single GUV Method Reveals Interaction of Tea Catechin (−)-Epigallocatechin Gallate with Lipid Membranes Biophysical Journal, Volume 92, Issue 9, 1 May 2007, Pages 3178-3194 Yukihiro Tamba, Shinya Ohba, Masayo Kubota, Hiroe Yoshioka, Hisashi Yoshioka and Masahito Yamazaki Abstract Tea catechins, which are flavonoids and the main components of green tea extracts, are thought to have antibacterial and antioxidant activity. Several studies indicate that lipid membranes are one of the targets of the antibacterial activity of catechins. Studies using a suspension of large unilamellar vesicles (LUVs) indicate that catechin causes gradual leakage of internal contents from LUVs. However, the detailed characteristics of the interaction of catechins with lipid membranes remain unclear. In this study, we investigated the interaction of (−)-epigallocatechin gallate (EGCg), a major catechin in tea extract, with single giant unilamellar vesicles (GUVs) of egg phosphatidylcholine (egg PC) using phase-contrast fluorescence microscopy and the single GUV method. We prepared GUVs of lipid membranes of egg PC in a physiological ion concentration (∼150mM NaCl) using the polyethylene glycol-lipid method. Low concentrations of EGCg at and above 30M induced rapid leakage of a fluorescent probe, calcein, from the inside of single egg PC-GUVs; after the leakage, the GUVs changed into small lumps of lipid membranes. On the other hand, phase-contrast microscopic images revealed the detailed process of the EGCg-induced burst of GUVs, the decrease in their diameter, and their transformation into small lumps. The dependence of the fraction of burst GUVs on EGCg concentration was almost the same as that of the fraction of leaked GUV. This correlation strongly indicates that the leakage of calcein from the inside to the outside of the GUV occurred as a result of the burst of the GUV. The fraction of completely leaked GUV and the fraction of the burst GUV increased with time and also increased with increasing EGCg concentration. We compared the EGCg-induced leakage from single GUVs with EGCg-induced leakage from a LUV suspension. The analysis of the EGCg-induced shape changes shows that the binding of EGCg to the external monolayer of the GUV increases its membrane area, inducing an increase in its surface pressure. Small angle x-ray scattering experiments indicate that the intermembrane distance of multilamellar vesicles of PC membrane greatly decreased at EGCg concentrations above the threshold, suggesting that neighboring membranes came in close contact with each other. On the basis of these results, we discuss the mechanism of the EGCg-induced bursting of vesicles. Abstract | Full Text | PDF (2572 kb) |
| Mitochondrial import: Crossing the aqueous intermembrane space Current Biology, Volume 8, Issue 8, 9 April 1998, Pages R262-R265 Nikolaus Pfanner Summary Mitochondrial protein import follows a general pathway for preproteins with amino-terminal presequences. The discovery of novel import components has now revealed a distinct pathway for translocation of hydrophobic proteins across the intermembrane space and into the inner membrane. Summary | Full Text | PDF (89 kb) |
Copyright © 1995 The Biophysical Society. All rights reserved.
Biophysical Journal, Volume 68, Issue 1, 157-163, 1 January 1995
doi:10.1016/S0006-3495(95)80170-0
Research Article
Y.S. Tarahovsky, A.A. Khusainov, R. Daugelavichus and E. Bakene
Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Puschchino.
This paper presents some further evidence for our model of DNA translocation into Escherichia coli cells by bacteriophage T4 (see Tarahovsky, Y. S., Khusainov, A. A., Deev, A. A., Kim, Y. V. 1991. FEBS Lett. 289:18–22). When lowering the temperature, we succeeded in slowing down the infection process and in observing a few separate stages by electron microscopy. Also, potassium leakage at different temperatures was measured. At 0–6 degrees C the phage was found to be irreversibly adsorbed on the cell surface, its tail to be contracted, and the outer membrane to be invaginated. Membrane fusion and formation of broad intermembrane bridges with a hole for potassium leakage were shown to start above 7 degrees C. At about 17–20 degrees C the diameter of the bridge decreased considerably, which could correspond to the sealing of the membrane.