Verification of the <i>Saccharina japonica</i> Translocon <i>Tic20</i> and its Localization in the Chloroplast Membrane in Diatoms

• Main Authors: Zhihang Chen, Xiuliang Wang, Shuang Li, Jianting Yao, Zhanru Shao, Delin Duan
• Format: Article
• Language: English
• Published: MDPI AG 2019-08-01
• Series: International Journal of Molecular Sciences
• Subjects: Tic20; EF-hand; <i>Phaeodactylum tricornutum</i>; <i>Saccharina japonica</i>; subcellular localization; transmembrane topology
• Online Access: https://www.mdpi.com/1422-0067/20/16/4000

Tic20 is an important translocon protein that plays a role in protein transport in the chloroplast. The sequence of Tic20 was determined in the lower brown alga <i>Saccharina japonica</i>. Structural analysis of SjTic20 revealed a noncanonical structure consisting of an N-terminal non-cyanobacterium-originated EF-hand domain (a helix-loop-helix structural domain) and a C-terminal cyanobacterium-originated Tic20 domain. Subcellular localization and transmembrane analysis indicated that SjTic20 featured an &#8220;M&#8221;-type N_in-C_in-terminal orientation, with four transmembrane domains in the innermost membrane of the chloroplast in the microalga <i>Phaeodactylum tricornutum</i>, and the EF-hand domain was entirely extruded into the chloroplast stroma. Our study provides information on the structure, localization, and topological features of SjTic20, and further functional analysis of SjTic20 in <i>S. japonica</i> is needed.