Arabidopsis synaptotagmin SYT1, a type I signal-anchor protein, requires tandem C2 domains for delivery to the plasma membrane.
The correct localization of integral membrane proteins to subcellular compartments is important for their functions. Synaptotagmin contains a single transmembrane domain that functions as a type I signal-anchor sequence in its N terminus and two calcium-binding domains (C(2)A and C(2)B) in its C terminus. Here, we demonstrate that the localization of an Arabidopsis synaptotagmin homolog, SYT1, to the plasma membrane (PM) is modulated by tandem C2 domains. An analysis of the roots of a transformant-expressing green fluorescent protein-tagged SYT1 driven by native SYT1 promoter suggested that SYT1 is synthesized in the endoplasmic reticulum, and then delivered to the PM via the exocytotic pathway. We transiently expressed a series of truncated proteins in protoplasts, and determined that tandem C(2)A-C(2)B domains were necessary for the localization of SYT1 to the PM. The PM localization of SYT1 was greatly reduced following mutation of the calcium-binding motifs of the C(2)B domain, based on sequence comparisons with other homologs, such as endomembrane-localized SYT5. The localization of SYT1 to the PM may have been required for the functional divergence that occurred in the molecular evolution of plant synaptotagmins.
Yamazaki
Tomokazu
T
21st Century Center of Excellence Program, Iwate University, Morioka, Iwate 020-8550, Japan.
Takata
Naoki
N
Uemura
Matsuo
M
Kawamura
Yukio
Y
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology* / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D017353:Gene Deletion; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism; D018517:Plant Roots / Q000166:cytology / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism; D050863:Synaptotagmin I / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*
D011993:Recombinant Fusion Proteins; D050863:Synaptotagmin I