Tic110 family

The Chloroplast Envelope Anion Channel-forming Tic110 (Tic110) Family (TC#1.A.18) consists of proteins of the inner chloroplast envelope membrane. This family consists of the inner membrane protein import apparatus, and appears to be a protein import-related anion-selective channel. It has also been designated (1) IEP110, (2) IAP100 and (3) protein import-related anion channel (PIRAC).

Location

Most of the Tic110 protein is probably in the intermembrane space.[1] Transport across the outer and inner membranes probably occurs by two independent processes.[2]

Structure

Arabidopsis thaliana Tic 110 is 996 amino acyl residues long and exhibits 2 putative transmembrane segments (TMSs) near its N-terminus at positions 74-92 and 101-120. Biochemical analyses suggest that this protein is part of a 600 kDa complex. Tic110 has two proposed functions with naturally exclusive structures; a protein-conducting channel with 6 TMSs, and a scaffold with 2 N-terminal TMSs followed by a large soluble domain for binding transit peptides and other stromal translocon components. The C-terminal half of Tic110 possesses a rod-shaped helix-repeat structure that is too flattened and elongated to be a channel. The structure is most similar to the HEAT-repeat motif that functions as scaffolds for protein-protein interactions.[3] The pore size was estimated to be about 6.5 Å.[4]

Transport Reaction

The transport reactions across the chloroplast inner membrane catalyzed by Tic110 are:

(1) anions (out) ⇌ anions (in)
(2) proteins (out) → proteins (in)

References
  1. Lübeck, J.; Soll, J.; Akita, M.; Nielsen, E.; Keegstra, K. (1996-08-15). "Topology of IEP110, a component of the chloroplastic protein import machinery present in the inner envelope membrane". The EMBO Journal. 15 (16): 4230–4238. doi:10.1002/j.1460-2075.1996.tb00797.x. ISSN 0261-4189. PMC 452148. PMID 8861951.
  2. Kessler, F.; Blobel, G. (1996-07-23). "Interaction of the protein import and folding machineries of the chloroplast". Proceedings of the National Academy of Sciences of the United States of America. 93 (15): 7684–7689. Bibcode:1996PNAS...93.7684K. doi:10.1073/pnas.93.15.7684. ISSN 0027-8424. PMC 38807. PMID 8755536.
  3. Tsai, Jia-Yin; Chu, Chiung-Chih; Yeh, Yi-Hung; Chen, Lih-Jen; Li, Hsou-Min; Hsiao, Chwan-Deng (2013-09-01). "Structural characterizations of the chloroplast translocon protein Tic110". The Plant Journal. 75 (5): 847–857. doi:10.1111/tpj.12249. ISSN 1365-313X. PMC 3823011. PMID 23711301.
  4. van den Wijngaard, P. W.; Vredenberg, W. J. (1999-09-03). "The envelope anion channel involved in chloroplast protein import is associated with Tic110". The Journal of Biological Chemistry. 274 (36): 25201–25204. doi:10.1074/jbc.274.36.25201. ISSN 0021-9258. PMID 10464239.

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