title: Transmembrane domain modulates sorting of membrane proteins in Toxoplasma gondii.
abstract: Overlapping mechanisms that function simultaneously in the intracellular sorting of mammalian membrane proteins often confound delineation of individual sorting pathways. By analyzing sorting in the evolutionarily simpler organism Toxoplasma gondii, we demonstrate a role for transmembrane domain (TMD) length in modulating the signal-dependent segregation of membrane proteins to distinct intracellular organelles. The dense granule localization of the single pass transmembrane protein GRA4 could be completely rerouted to the Golgi and cell surface simply by replacement of its TMD with that from either vesicular stomatitis virus G or the low density lipoprotein (LDL) receptor. Mutational and biochemical analyses suggested that this effect was not caused by any specific sequence motif or strength of membrane association of the GRA4 TMD. Instead, a property imparted by the vesicular stomatitis virus G or LDL receptor TMDs, both of which are longer than the GRA4 TMD, appeared to be a decisive factor. Indeed, shortening the LDL receptor TMD to a length similar to that of GRA4 resulted in dense granule localization, whereas lengthening the GRA4 TMD resulted in rerouting to the Golgi. From these data, we conclude that although the TMD may not necessarily be a sole determinant in membrane protein sorting, its properties can markedly modulate the utilization of more conventional signal-mediated sorting pathways.
authors.affiliation: Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
authors.forename: Verena
authors.initials: V
authors.lastname: Karsten
authors.forename: Ramanujan S
authors.initials: RS
authors.lastname: Hegde
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Sinai
authors.forename: Mei
authors.initials: M
authors.lastname: Yang
authors.forename: Keith A
authors.initials: KA
authors.lastname: Joiner
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D004252:DNA Mutational Analysis; D006056:Golgi Apparatus / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D007930:Leucine / Q000737:chemistry; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011817:Rabbits; D011973:Receptors, LDL / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014122:Toxoplasma / Q000378:metabolism*; D014709:Vero Cells; D014759:Viral Envelope Proteins / Q000378:metabolism
chemical_list: C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D011973:Receptors, LDL; D011993:Recombinant Fusion Proteins; D014759:Viral Envelope Proteins; D007930:Leucine