Abstract
Previously, we showed that the proton permeability of small unilamellar vesicles (SUVs) composed of polar lipid fraction E (PLFE) from the thermoacidophilic archaeon Sulfolobus acidocaldarius was remarkably low and insensitive to temperature (Komatsu and Chong 1998). In this study, we used photon correlation spectroscopy to investigate the time dependence of PLFE SUV size as a function of Ca2+ concentration. In the absence of Ca2+, vesicle diameter changed little over 6 months. Addition of Ca2+, however, immediately induced formation of vesicle aggregates with an irregular shape, as revealed by confocal fluorescence microscopy. Aggregation was reversible upon addition of EDTA; however, the reversibility varied with temperature as well as incubation time with Ca2+. Freeze-fracture electron microscopy showed that, after a long period of incubation (2 weeks) with Ca2+, the PLFE vesicles had not just aggregated, but had fused or coalesced. The initial rate of vesicle aggregation varied sigmoidally with Ca2+ concentration. At pH 6.6, the threshold calcium concentration (Cr) for vesicle aggregation at 25 and 40 degrees C was 11 and 17 mM, respectively. At pH 3.0, the Cr at 25 degrees C increased to 25 mM. The temperature dependence of Cr may be attributable to changes in membrane surface potential, which was -22.0 and -13.2 mV at 25 and 40 degrees C, respectively, at pH 6.6, as determined by 2-(p-toluidinyl)naphthalene-6-sulfonic acid fluorescence. The variation in surface potential with temperature is discussed in terms of changes in lipid conformation and membrane organization.
Highlights
The major lipid components of the plasma membrane of the thermoacidophilic archaeon Sulfolobus acidocaldarius are tetraether lipids (De Rosa et al 1986, Langworthy and Pond 1986, Kates 1992), among which the polar lipid fraction E (PLFE) is the main constituent (Lo and Chang 1990)
PLFE contains a mixture of bipolar tetraether lipids with either a glycerol dialkyl calditol tetraether (GDNT; called calditoglycerocaldarchaeol) or a glycerol dialkyl glycerol tetraether (GDGT; called caldarchaeol) skeleton (Figure 1) (Lo and Chang 1990, Sugai et al 1995, Gliozzi et al 2002)
We have focused on the calcium-induced aggregation of PLFE liposomes derived from the thermoacidophilic archaeon S. acidocaldarius
Summary
The major lipid components of the plasma membrane of the thermoacidophilic archaeon Sulfolobus acidocaldarius are tetraether lipids (De Rosa et al 1986, Langworthy and Pond 1986, Kates 1992), among which the polar lipid fraction E (PLFE) is the main constituent (Lo and Chang 1990). The. PLFE contains a mixture of bipolar tetraether lipids with either a glycerol dialkyl calditol tetraether (GDNT; called calditoglycerocaldarchaeol) or a glycerol dialkyl glycerol tetraether (GDGT; called caldarchaeol) skeleton (Figure 1) (Lo and Chang 1990, Sugai et al 1995, Gliozzi et al 2002). PLFE contains a mixture of bipolar tetraether lipids with either a glycerol dialkyl calditol tetraether (GDNT; called calditoglycerocaldarchaeol) or a glycerol dialkyl glycerol tetraether (GDGT; called caldarchaeol) skeleton (Figure 1) (Lo and Chang 1990, Sugai et al 1995, Gliozzi et al 2002) Both GDGT and GDNT have bisubstituted polar head groups and are designated bipolar tetraether lipids. The number of cyclopentane rings increases with increasing growth temperature (De Rosa et al 1980)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
