title: N-glycosylation enables high lateral mobility of GPI-anchored proteins at a molecular crowding threshold.
abstract: The protein density in biological membranes can be extraordinarily high, but the impact of molecular crowding on the diffusion of membrane proteins has not been studied systematically in a natural system. The diversity of the membrane proteome of most cells may preclude systematic studies. African trypanosomes, however, feature a uniform surface coat that is dominated by a single type of variant surface glycoprotein (VSG). Here we study the density-dependence of the diffusion of different glycosylphosphatidylinositol-anchored VSG-types on living cells and in artificial membranes. Our results suggest that a specific molecular crowding threshold (MCT) limits diffusion and hence affects protein function. Obstacles in the form of heterologous proteins compromise the diffusion coefficient and the MCT. The trypanosome VSG-coat operates very close to its MCT. Importantly, our experiments show that N-linked glycans act as molecular insulators that reduce retarding intermolecular interactions allowing membrane proteins to function correctly even when densely packed.
authors.affiliation: Department of Cell and Developmental Biology, Theodor-Boveri-Institute, Biocenter, University of Würzburg, Würzburg 97074, Germany.
authors.forename: Andreas J W
authors.initials: AJ
authors.lastname: Hartel
authors.affiliation: Department of Cell and Developmental Biology, Theodor-Boveri-Institute, Biocenter, University of Würzburg, Würzburg 97074, Germany.
authors.forename: Marius
authors.initials: M
authors.lastname: Glogger
authors.affiliation: Department of Cell and Developmental Biology, Theodor-Boveri-Institute, Biocenter, University of Würzburg, Würzburg 97074, Germany.
authors.forename: Nicola G
authors.initials: NG
authors.lastname: Jones
authors.affiliation: Physical Chemistry of Biosystems, Institute of Physical Chemistry, University of Heidelberg, Heidelberg 69120, Germany.
authors.forename: Wasim
authors.initials: W
authors.lastname: Abuillan
authors.affiliation: Department of Cell and Developmental Biology, Theodor-Boveri-Institute, Biocenter, University of Würzburg, Würzburg 97074, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Batram
authors.affiliation: Department of Cell and Developmental Biology, Theodor-Boveri-Institute, Biocenter, University of Würzburg, Würzburg 97074, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Hermann
authors.affiliation: Department of Cell and Developmental Biology, Theodor-Boveri-Institute, Biocenter, University of Würzburg, Würzburg 97074, Germany.
authors.forename: Susanne F
authors.initials: SF
authors.lastname: Fenz
authors.affiliation: Physical Chemistry of Biosystems, Institute of Physical Chemistry, University of Heidelberg, Heidelberg 69120, Germany.|Institute for Integrated Cell-Material Science (WPI iCeMS), Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Motomu
authors.initials: M
authors.lastname: Tanaka
authors.affiliation: Department of Cell and Developmental Biology, Theodor-Boveri-Institute, Biocenter, University of Würzburg, Würzburg 97074, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Engstler
mesh_terms: D006031:Glycosylation; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D014345:Trypanosoma; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000502:physiology*
chemical_list: D017261:Glycosylphosphatidylinositols; D014643:Variant Surface Glycoproteins, Trypanosoma