The synaptic vesicle protein SV31 assembles into a dimer and transports Zn2

J Neurochem. 2017 Jan;140(2):280-293. doi: 10.1111/jnc.13886. Epub 2016 Dec 5.

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 Km value 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.

Keywords: SV31; Zn2+ binding and transport; cell free; dimerization; membrane protein; synaptic vesicles.

MeSH terms

  • Animals
  • Biological Transport
  • Cations, Divalent / metabolism
  • Membrane Proteins / metabolism*
  • Membrane Transport Proteins / metabolism
  • Mutagenesis, Site-Directed / methods
  • Nerve Tissue Proteins / metabolism*
  • Protein Multimerization
  • Rats
  • Synaptic Vesicles / metabolism*
  • Zinc / metabolism*

Substances

  • Cations, Divalent
  • Membrane Proteins
  • Membrane Transport Proteins
  • Nerve Tissue Proteins
  • Tmem163 protein, rat
  • Zinc