Plasma membrane intrinsic proteins of Beta vulgaris L.
The plasma membrane (PM) of higher plants contains numerous proteins; however, due to their low abundance, only a few have been identified and characterized by direct biochemical approaches. The major intrinsic protein (MIP) family is a class of highly hydrophobic integral membrane proteins thought to function as channels that facilitate the passage of water, small solutes, and possibly other moieties through the membrane. A family of PM intrinsic proteins was purified and characterized from PM vesicles derived from storage tissue of Beta vulgaris L. using the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate. This PM intrinsic protein-enriched fraction also contains high levels of UDP-glucose:(1,3)-beta-glucan (callose) synthase activity. Dithiothreitol is required to visualize the monomeric species of these highly hydrophobic integral membrane proteins. Sequence analysis of tryptic fragments derived from polypeptides of 31 and 27 kD revealed significant homologies to plant MIPs identified from cloned sequences. These MIPs include clone 7a from pea and RD28 from Arabidopsis, both of which are water-stress proteins, a tomato ripening-associated membrane protein, and PIP 2b, a PM-bound water channel protein from Arabidopsis. MIPs, therefore, represent abundantly occurring components of PMs derived from beet storage tissue.
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Department of Food Science, New Jersey Agricultural Experiment Station, Cook College, Rutgers University, New Brunswick 08903-0231, USA.
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Wasserman
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D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005964:Glucosyltransferases / Q000302:isolation & purification / Q000378:metabolism; D015151:Immunoblotting; D008565:Membrane Proteins / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D010944:Plants / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins; D017386:Sequence Homology, Amino Acid
D008565:Membrane Proteins; D010446:Peptide Fragments; D010940:Plant Proteins; D029702:Schizosaccharomyces pombe Proteins; D005964:Glucosyltransferases; C020570:1,3-beta-glucan synthase