Membrane proteins detergent-resistant fractions

Borner et al. (2005) took a different approach to address the specific localization of DRM proteins to lipid rafts. In this smdy the relative enrichment of proteins in the detergent-resistant fraction versus total cell membranes was used as a measure of the specificity of putative lipid raft proteins. In their study Bomer et al. used Arabidopsis thaliana as the model system so a direct comparison with mammalian DRM reports is difficult and perhaps unfair since it is not always clear what the human homologue of a plant protein is. However, it is interesting to note that Bomer et al. also found that the common contaminants in DRMs are certain highly abundant mitochondrial and endoplasmic reticulum proteins. 

FIG U RE 20.5 Two-dimensional eleciropherogtams of each differential detergent fraction. The digitonin fraction (A) is the cytosolic proteins, the Triton fraction (B) is the membrane/organelle proteins, the Tween fraction (C) is the nuclear-membrane proteins, and the detergent resistant fraction (D) is the eytoskeletal proteins. (Reprinted from Fazal,M. A., etal.,7. Chromatogr. A, 1130,182-189, 2006. Copyright 2006. With permission from Elsevier.)... 

Both mPA-PLAjU and mPA-PLAj/ , like many phosphate-recognizing enzymes such as phosphatase and ATPase [40], are inhibited by vanadate [51]. When expressed in insect Sf9 cells, neither mPA-PLAja nor mPA-PLAj/ were secreted. Both were recovered from the Triton X-lOO-insoluble fraction of the cell membrane. An immunofluorescence analysis confirmed that these proteins are localized exclusively to the plasma membrane. Both mPA-PLAja and -fi may locahze in the detergent-resistant membrane domain, referred to as raft structures, and function as lysoPA-producers under certain conditions [51]. 

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