title: Molecular and structural transmembrane determinants critical for embedding claudin-5 into tight junctions reveal a distinct four-helix bundle arrangement.
abstract: The mechanism of TJ (tight junction) assembly and the structure of TJ strand-forming Cldns (claudins) are unclear. To identify determinants of assembly of blood-brain barrier-related Cldn3 and Cldn5, chimaeric mutants were analysed by cellular reconstitution of TJ strands and live-cell imaging. On the basis of the rescue of mutants deficient for strand formation, we identified Cldn5 residues (Cys128, Ala132, Ile142, Ala163, Ile166 and Leu174) involved in Cldn folding and assembly. Experimental results were combined with structural bioinformatics approaches. Initially the experimentally validated previous model of the ECL2 (extracellular loop 2) of Cldn5 was extended to the flanking transmembrane segments (TM3/TM4). A coiled-coil interface probably caused by alternating small and large residues is supported by concomitant knob-into-hole interactions including Cldn5-specific residues identified in the present paper. To address arrangement of the TMs in a four-helix bundle, data from evolutionary sequence couplings and comparative modelling of intramolecular interfaces in the transmembrane region of Cldns led to a complete Cldn5 model. Our suggested Cldn subtype-specific intramolecular interfaces that are formed by conserved coiled-coil motifs and non-conserved residues in distinct TM positions were confirmed by the recently released crystal structure of Cldn15. The identified molecular and structural determinants essentially contribute to assembly of Cldns into TJ strands.
authors.affiliation: *Leibniz-Institut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Rossa
authors.affiliation: *Leibniz-Institut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany.
authors.forename: Jonas
authors.initials: J
authors.lastname: Protze
authors.affiliation: *Leibniz-Institut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Kern
authors.affiliation: *Leibniz-Institut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Piontek
authors.affiliation: †Institute of Clinical Physiology, Charité-Universitätsmedizin Berlin, 12203 Berlin, Germany.
authors.forename: Dorothee
authors.initials: D
authors.lastname: Günzel
authors.affiliation: *Leibniz-Institut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Krause
authors.affiliation: †Institute of Clinical Physiology, Charité-Universitätsmedizin Berlin, 12203 Berlin, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Piontek
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D062507:Claudin-5 / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D019108:Tight Junctions / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism
chemical_list: D062507:Claudin-5; C491511:Cldn5 protein, mouse