Laboratory of Organelle Biology


Associate Professor Masato NAKAI



Tel 81-6-6879-8612
Fax 81-6-6879-8613


In plants and algae, the eukaryotes, photosynthesis is carried out in a specialized organelle called chloroplast. It is now widely accepted that virtually all chloroplasts in today’s photosynthetic eukaryotes derive from one fairly rare primary endosymbiotic event with a cyanobacterium-like ancestor thought to have occurred more than a billion years ago. In the course of evolution, massive transfer of genes from the endosymbiont to the host’s nuclear genome occurred, accompanied with the development of the protein transport system that allows these nuclear-encoded chloroplast proteins back into the endosymbiont. Extant higher plants can synthesize only ~100 proteins inside the chloroplast but must import such 2000-3000 different cytosolically-synthesized nuclear-encoded proteins, across the double envelope membranes surrounding this organelle, to fulfill their complex physiological roles including photosynthetic functions. Two successive protein translocons at the outer and inner envelope membranes, termed TOC and TIC, respectively, are responsible for the task of protein import into chloroplasts. Our recent discovery of the genuine TIC translocon which are well conserved among most land plants as well as green algae could provide us an entirely revised view on the molecular mechanisms of protein translocation across the inner envelope membrane of chloroplasts and also novel insights on the evolution of the chloroplast protein import system.


image1_e_Laboratory of Organelle Biology


Current Research Programs

1. Molecular studies on chloroplast biogenesis.
2. Elucidation of molecular mechanisms of protein translocation across the envelope membranes of chloroplasts.
3. Molecular evolutionary studies on the chloroplast protein import system.


1. The TIC complex uncovered: The alternative view on the molecular mechanism of protein translocation across the inner envelope membrane of chloroplasts. Nakai M. (2015) Biochim Biophys Acta 1847, 957-967.

2. YCF1: A Green TIC. Nakai M. (2015) Plant Cell 27, 1834-1838.

3. Unconvering the Protein Translocon at the Chloroplast Inner Envelope Membrane. Kikuchi S, Nakai M, et al. (2013) Science 339, 571-574.
4. In vivo studies on the roles of two closely related Arabidopsis Tic20 proteins, AtTic20-I and AtTic20-IV. Hirabayashi Y, Kikuchi S, Oishi M, Nakai M. (2011) Plant Cell Physiol., 52, 469-478.
5. A 1-megadalton translocation complex containing Tic20 and Tic21 mediates chloroplast protein import at the inner envelope membrane. Kikuchi S, Oishi M, Hirabayashi Y, Nakai M, et al. (2009) Plant Cell 21, 1781-1797.