Clustering and lateral concentration of raft lipids by the MAL protein.
MAL, a compact hydrophobic, four-transmembrane-domain apical protein that copurifies with detergent-resistant membranes is obligatory for the machinery that sorts glycophosphatidylinositol (GPI)-anchored proteins and others to the apical membrane in epithelia. The mechanism of MAL function in lipid-raft-mediated apical sorting is unknown. We report that MAL clusters formed by two independent procedures-spontaneous clustering of MAL tagged with the tandem dimer DiHcRED (DiHcRED-MAL) in the plasma membrane of COS7 cells and antibody-mediated cross-linking of FLAG-tagged MAL-laterally concentrate markers of sphingolipid rafts and exclude a fluorescent analogue of phosphatidylethanolamine. Site-directed mutagenesis and bimolecular fluorescence complementation analysis demonstrate that MAL forms oligomers via xx intramembrane protein-protein binding motifs. Furthermore, results from membrane modulation by using exogenously added cholesterol or ceramides support the hypothesis that MAL-mediated association with raft lipids is driven at least in part by positive hydrophobic mismatch between the lengths of the transmembrane helices of MAL and membrane lipids. These data place MAL as a key component in the organization of membrane domains that could potentially serve as membrane sorting platforms.
Magal
Lee Goldstein
LG
Department of Pathology, Tel-Aviv University, Israel.
Yaffe
Yakey
Y
Shepshelovich
Jeanne
J
Aranda
Juan Francisco
JF
de Marco
Maria del Carmen
Mdel C
Gaus
Katharina
K
Alonso
Miguel Angel
MA
Hirschberg
Koret
K
D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D017261:Glycosylphosphatidylinositols / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism*; D021962:Membrane Microdomains / Q000737:chemistry* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009185:Myelin Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D011487:Protein Conformation; D011510:Proteolipids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
D017261:Glycosylphosphatidylinositols; C569026:MAL protein, human; D008563:Membrane Lipids; D026901:Membrane Transport Proteins; D009185:Myelin Proteins; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D011510:Proteolipids; D011993:Recombinant Fusion Proteins