Journal
EUROPEAN JOURNAL OF BIOCHEMISTRY
Volume 267, Issue 24, Pages 6989-6995Publisher
BLACKWELL SCIENCE LTD
DOI: 10.1046/j.1432-1327.2000.01776.x
Keywords
freeze-fracture; G protein; GPI-anchored; plant; plasma membrane
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Low density Triton X-100-insoluble plasma membrane microdomains can be isolated from different mammalian cell types and are proposed to be involved in membrane trafficking, cell morphogenesis and signal transduction. Heterotrimeric G-proteins and their receptors are often associated with such domains, suggesting that these structures are involved in G-protein-coupled signaling. Here we report that detergent-insoluble plasma membrane microdomains also exist in higher plants and contain about 15% of membrane-bound heterotrimeric G-protein beta-subunit (G beta). Plasma membrane microdomains were isolated from tobacco leaves. They have low buoyant density relative to the surrounding plasma membrane, and are insoluble in Triton X-100 at 4 degreesC. Detergent-insoluble vesicles were examined by freeze-fracture electron microscopy. They have sizes in the range 100-400 nm, and often contain aggregated protein complexes. The majority of plasma membrane proteins cannot be detected in the Triton X-100-insoluble fraction, while few polypeptides are highly enriched. We identified six proteins with molecular masses of 22, 28, 35, 60, 67 and 94 kDa in detergent-insoluble fractions that are glycosylphosphatidylinositol (GPI)-anchored.
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