Model Systems

In recent years, several papers have appeared which described the use of giant vesicles as model systems to address biophysical aspects of mainly lipid-lipid, but also lipid-DNA and lipid-protein interactions (Wick et al. 1996; Bucher et al. 1998; Longo et al. 1998; Angelova et al. 1999; Bagatolli and Gratton 1999, 2000a,b; Korlach et al. 1999; Bagatolli et al. 2000, 2002; Holopainen et al. 2000; Dietrich et al. 2001; Feigenson and Buboltz 2001; Fahsel et al. 2002; Nag et al. 2002; Sanchez et al. 2002; Veatch and Keller 2002, 2003; Koster et al. 2003; Scherfeld et al. 2003; Bacia et al. 2004a, b; Bernardino de la Serna et al. 2004; Girard et al. 2004; Janosch et al. 2004; Kahya et al. 2004; Veatch et al. 2004). One of the reasons why giant vesicles are suitable membrane model systems is their size, on the order of a few tens of micrometers, similar to the size of the plasma membrane of cells. Owing to their size, single vesicles can be directly observed using microscopy-related techniques (such as fluorescence microscopy). Additionally, because experiments are performed at the level of single vesicles, heterogeneity in shape and size and the presence of multilamellar vesicles are ruled out.

One of the significant aspects in using giant vesicles as model systems is the ability to control the molecular composition of the membrane as well as the environmental conditions. For instance, studies of the lateral structure of membranes using giant vesicles as model systems were normally confined to giant vesicles composed of artificial lipids or their mixtures with no more than three to four components (Bagatolli and Gratton 1999, 2000a,b; Korlach et al. 1999; Feigenson and Buboltz 2001; Dietrich et al. 2001; Veatch and Keller 2002, 2003; Kahya et al. 2004). However, as recently reported in the literature, it is also possible to form giant vesicles from natural lipid extracts (Bagatolli et al. 2000; Dietrich et al. 2001; Nag et al. 2002) and native membranes (Bernardino de la Serna et al. 2004). Additionally, incorporation of membrane proteins into giant unilamellar vesicles (GUVs) composed of lipid mixtures can also be performed (Kahya et al. 2001; Bacia et al. 2004b; Girard et al. 2004; Koster et al. 2003). ttis last fact allows one to establish an interesting strategy, i.e., to perform comparative studies among artificial lipid mixtures, natural lipid mixtures (both with and without membrane proteins) and finally membranes containing the full composition under controlled environmental conditions (Bernardino de la Serna et al. 2004). tte reader can find additional information about the giant vesicle field in an excellent review by Menger and Keiper (1998) and a book completely devoted to giant vesicles edited by Luisi and Walde (2000).

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