Membrane lateral heterogeneity

Andersson, B. and Anderson J.M. 1980. Lateral heterogeneity in the distribution of chlorophyll-protein complexes of the thylakoid membranes of spinach chloroplasts. Biochim. Biophys. Acta 593.427-440. 

This review focusses on certain aspects of the transverse arrangement of the proteins and lipids of thylakoid membranes, and the lateral heterogeneity of these complexes between the appressed and non-appressed regions of Chi b-containing plants. The consequences of lateral heterogeneity will also be examined with the emphasis on areas under debate. 

Early fractionation studies with thylakoids that had been fragmented by detergents [54] or mechanical means [55] followed by collection of the thylakoid submembrane fractions by centrifugation provided the first evidence for lateral heterogeneity. Submembrane fractions derived from granal stacks were enriched in PS II but they also contained PS 1, whereas the stroma thylakoids had mainly PS I. Sane et al. [55] proposed that appressed membranes were the site of non-cyclic electron transport, while the non-appressed membranes carried out cyclic photo-... 

Lateral heterogeneity has profound consequences for thylakoid function and structure [4,6,63] despite some uncertainty prevailing as to the absolute extent of lateral heterogeneity of the PS I complex, and the location of the Cyt 6//complex in both appressed and non-appressed membrane regions. 

B Andersson and JM Anderson (1980) Lateral heterogeneity in the distribution of chlorophyll-protein complexes of the thylakoid membranes of spinach chloroplasts. Biochim Biophys Acta 593 427-440 P-" Albertsson (1985) Partition of Cell Particles and Macromolecules (3rd edition) John Wiley H-E "kerlund, B Andersson and P-" Albertsson (1976) Isolation of photosystem II enriched membrane vesicles from spinach chloroplasts by phase partition. Biochim Biophys Acta 449 525-535 P Grber, A Zickler and H-E "kerlund (1978) Electric evidence for the isolation of inside-out vesicles from spinach chloroplasts. FEES Lett 96 233-237... 

The existence of microdomains within a membrane creates lateral heterogeneity that has consequences in terms of local concentrations of membrane-associated compounds, including membrane-active drugs, and the cooperativity between membrane proteins. It also causes fluctuations in the physicochemical properties of bilayers, including chemical interactions in the interfacial head group regions. These fluctuations can have profound effects on protein function and drug availability. 

Our results reveal two classes of PSII proteins those that are present only in grana lamellae, and those that display lateral heterogeneity in the thylakoids. The LHCII and the three PSII reaction center proteins, 32 kDa, D2 and cytochrome b559 are present both in grana and stroma lamellae. Such distribution is in agreement with previous reports on the dual location of PSII centers in the two membrane regions (1-3). In contrast, we find that the 51 kDa and 43 kDa PSII proteins are located exclusively in grana lamellae. 

The problem of the adequate determination of internal pH is complicated in the heterogeneous populations of vesicles. Chloroplasts are a typical example of such systems. According to electron microscopy data, there are at least two morphologically different membrane systems stroma- and grana-exposed thylakoids (see the sketch in Fig. 3.7). The numerous data in the last two decades brought evidence of the lateral heterogeneity of the chloroplasts lamellar system (see references [60-69]). Stroma- and grana-exposed thylakoids differ with respect to the content of the electron transport and the ATP-synthase complexes. 

Several approaches have been adopted to assess the lateral heterogeneity of acyl lipids in the thylakoid membrane (for reports published until Sept. 1984, see ref. in Siegenthaler and Rawyler ) ... 

In conclusion, the thylakoid membrane is characterized by considerable lateral heterogeneities in the distribution of all major membrane components, including acyl lipids. 

These particle-free areas occur concomitant with the formation of gel-phase lipids.The formation of mlcrodomalns In the plane of a cell membrane Is an Indication that lateral heterogeneity In organization can occur within membranes. These lateral phase separations can also be... 

---