Arabidopsis Synaptotagmin SYT1, a Type I Signal-anchor Protein,Requires Tandem C2 Domains for Delivery to the Plasma Membrane |
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Authors: | Tomokazu Yamazaki Naoki Takata Matsuo Uemura Yukio Kawamura |
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Institution: | From the ‡21st Century Center of Excellence Program.;¶Cryobiofrontier Research Center, Faculty of Agriculture, and ;§United Graduate School of Agricultural Sciences, Iwate University, Morioka, Iwate 020-8550, Japan |
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Abstract: | 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 (C2A and C2B) 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 C2A-C2B 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 C2B 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. |
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Keywords: | Arabidopsis Membrane Biogenesis Membrane Proteins Plant Plasma Membrane Protein Targeting C2 Domain Synaptotagmin |
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