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First published online August 19, 2005; 10.1104/pp.105.063198 Plant Physiology 139:287-295 (2005) © 2005 American Society of Plant Biologists A Novel Plant Major Intrinsic Protein in Physcomitrella patens Most Similar to Bacterial Glycerol Channels1Department of Plant Biochemistry, Centre for Chemistry and Chemical Engineering, Lund University, SE221 00 Lund, Sweden (S.G., K.N., U.J.); and Unité de Biochimie Physiologique, Institut des Sciences de la Vie, Université Catholique de Louvain, B1348 Louvain-la-Neuve, Belgium (A.-S.L., F.C.)
A gene encoding a novel fifth type of major intrinsic protein (MIP) in plants has been identified in the moss Physcomitrella patens. Phylogenetic analyses show that this protein, GlpF-like intrinsic protein (GIP1;1), is closely related to a subclass of glycerol transporters in bacteria that in addition to glycerol are highly permeable to water. A likely explanation of the occurrence of this bacterial-like MIP in P. patens is horizontal gene transfer. The expressed P. patens GIP1;1 gene contains five introns and encodes a unique C-loop extension of approximately 110 amino acid residues that has no obvious similarity with any other known protein. Based on alignments and structural comparisons with other MIPs, GIP1;1 is suggested to have retained the permeability for glycerol but not for water. Studies on heterologously expressed GIP1;1 in Xenopus laevis oocytes confirm the predicted substrate specificity. Interestingly, proteins of one of the plant-specific subgroups of MIPs, the NOD26-like intrinsic proteins, are also facilitating the transport of glycerol and have previously been suggested to have evolved from a horizontally transferred bacterial gene. Further studies on localization and searches for GIP1;1 homologs in other plants will clarify the function and significance of this new plant MIP.
1 This work was supported by the Erik Philip-Sörensen Foundation and the Swedish Research Council for Environment, Agricultural Sciences, and Spatial Planning (FORMAS; grants to U.J.) and by the Belgian Fund for Scientific Research and the Interuniversity Attraction Poles Programme-Belgian Science Policy (grants to F.C.). Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.063198. * Corresponding author; e-mail urban.johanson{at}plantbio.lu.se; fax 46462224116. Received March 22, 2005; returned for revision June 12, 2005; accepted June 16, 2005. Related articles in Plant Physiol.:
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