title: Targeting and biogenesis of transporters and channels in chloroplast envelope membranes: Unsolved questions.
abstract: Chloroplasts produce carbohydrates, hormones, vitamins, amino acids, pigments, nucleotides, ATP, and secondary metabolites. Channels and transporters are required for the movement of molecules across the two chloroplast envelope membranes. These transporters and channel proteins are grouped into two different types, including β-barrel proteins and transmembrane-domain (TMD) containing proteins. Most β-barrel proteins are localized at the outer chloroplast membrane, and TMD-containing proteins are localized at the inner chloroplast membrane. Many of these transporters and channels are encoded by nuclear genes; therefore, they have to be imported into chloroplasts after translation on cytosolic ribosomes. These proteins should have specific targeting signals for their final destination in the chloroplast membrane and for assembly into specific complexes. In this review, we summarize recent progress in the identification, functional characterization, and biogenesis of transporters and channels at the chloroplast envelope membranes, and discuss outstanding questions regarding transporter and channel protein biogenesis.
authors.affiliation: Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea.
authors.forename: Young Jun
authors.initials: YJ
authors.lastname: Oh
authors.affiliation: Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea; Department Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea. Electronic address: ihhwang@postech.ac.kr.
authors.forename: Inhwan
authors.initials: I
authors.lastname: Hwang
mesh_terms: D017360:Arabidopsis / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D017136:Ion Transport; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D026901:Membrane Transport Proteins; D002118:Calcium
keywords: Biogenesis; Chloroplasts; Molecular machinery for biogenesis; Outer and inner envelope membranes; Targeting signals; Transporters and channels