Substitution of the two carboxyl-terminal serines by alanine causes retention of MAL, a component of the apical sorting machinery, in the endoplasmic reticulum.
MAL, a selective resident of glycolipid-enriched membranes (GEMs), is an integral membrane protein necessary for apical transport and accurate sorting of the influenza virus hemagglutinin in MDCK cells. The carboxyl-terminal end of MAL has the sequence Phe-Ser-Leu-Ile-Arg-Trp-Lys-Ser-Ser (FSLIRWKSS), which includes the LIRW motif necessary for sorting MAL to GEMs, and whose last five amino acids resemble dilysine-based signals involved in endoplasmic reticulum (ER) retention. We have addressed the influence of the carboxyl-terminal serines in both MAL distribution and incorporation into GEMs. Substitution of the serines by alanine impeded the access of MAL to GEMs and changed its distribution from a perinuclear distribution to an ER pattern. The RWKSS sequence appended to the carboxyl-terminus of CD4 caused retention of the chimera in the ER. Thus, although this pentapeptide can function producing ER retention in other protein context, the presence of the carboxyl-terminal serines in the intact MAL molecule prevents its use as an ER-retention signal.
Puertollano
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Centro de Biología Molecular "Severo Ochoa,", Universidad Autónoma de Madrid, Consejo Superior de Investigaciones Científicas, Cantoblanco, Madrid, 28049-, Spain.
Alonso
M A
MA
D000409:Alanine / Q000502:physiology*; D000818:Animals; D015704:CD4 Antigens / Q000378:metabolism; D019556:COS Cells; D002135:Calcium-Binding Proteins / Q000378:metabolism; D037281:Calnexin; D051242:Caveolin 1; D022461:Caveolins; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D006825:Hybridomas; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D051379:Mice; D016296:Mutagenesis; D009185:Myelin Proteins; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D011510:Proteolipids / Q000737:chemistry / Q000378:metabolism*; D012694:Serine / Q000502:physiology*
D015704:CD4 Antigens; D002135:Calcium-Binding Proteins; D051242:Caveolin 1; D022461:Caveolins; C569026:MAL protein, human; C569027:Mal protein, mouse; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009185:Myelin Proteins; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D011510:Proteolipids; D037281:Calnexin; D012694:Serine; D000409:Alanine