title: The synaptic vesicle protein SV31 assembles into a dimer and transports Zn2.
abstract: The integral synaptic vesicle protein SV31 has been shown to bind divalent cations. Here, we demonstrate that SV31 protein synthesized within a cell-free system binds Zn2+and to a lower extent Ni2+and Cu2+ions. Expression with Zn2+stabilized the protein and increased solubility. SV31 was preferentially monomeric in detergent and revealed specific binding of Zn2+. When co-translationally inserted into defined nanodisc bilayers, SV31 assembled into dimeric complexes, resulting in increased binding of Zn2+. Putative Zn2+-binding motifs within SV31 comprise aspartic acid and histidine residues. Site-directed mutagenesis of two conserved aspartic acid residues leads to a potent decrease in Zn2+binding but did not affect dimerization. Chemical modification of histidine residues abolished some of the Zn2+-binding capacity. We demonstrate proton-dependent transport of Zn2+as by accumulation of fluorescent FluoZin-1 inside of SV31-containing proteoliposomes. Transport activity has a Kmvalue of 44.3 μM and required external Zn2+and internal acidic pH. Our results demonstrate that the synaptic vesicle-integral protein SV31 functions as a proton-dependent Zn2+transporter. SV31 may attribute specific and yet undiscovered functions to subsets of synapses.
authors.affiliation: Institute of Cell Biology and Neuroscience, Goethe-University, Frankfurt am Main, Germany.
authors.forename: Lisa
authors.initials: L
authors.lastname: Waberer
authors.affiliation: Institute of Biophysical Chemistry, Centre for Biomolecular Magnetic Resonance, Goethe-University, Frankfurt am Main, Germany.
authors.forename: Erik
authors.initials: E
authors.lastname: Henrich
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe-University, Frankfurt am Main, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Peetz
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe-University, Frankfurt am Main, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Morgner
authors.affiliation: Institute of Biophysical Chemistry, Centre for Biomolecular Magnetic Resonance, Goethe-University, Frankfurt am Main, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Dötsch
authors.affiliation: Institute of Biophysical Chemistry, Centre for Biomolecular Magnetic Resonance, Goethe-University, Frankfurt am Main, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Bernhard
authors.affiliation: Institute of Cell Biology and Neuroscience, Goethe-University, Frankfurt am Main, Germany.
authors.forename: Walter
authors.initials: W
authors.lastname: Volknandt
mesh_terms: D000818:Animals; D001692:Biological Transport; D002413:Cations, Divalent / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D055503:Protein Multimerization; D051381:Rats; D013572:Synaptic Vesicles / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; C523973:Tmem163 protein, rat; D015032:Zinc
keywords: SV31; Zn2+ binding and transport; cell free; dimerization; membrane protein; synaptic vesicles