Protein Import Into Chloroplasts: Who, When, and How?

Vothknecht, Ute C.; Soll, Jürgen

doi:10.1007/978-1-4020-4061-0_3

Cited by 5 publications

(2 citation statements)

References 152 publications

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“…If one assumes that the chloroplast vesicle system was adopted from the cytosol of its endosymbiotic host, it could have needed modifications which prokaryotic proteins may have evolved to fulfill. If so, it would be similar to the protein import machinery where TOC and TIC protein components are of both prokaryotic and eukaryotic origin (Celedon and Cline 2013 ; Keeling 2013 ; Vothknecht and Soll 2007 ). The evolutionary benefit of a chloroplast vesicle system could be to gain a repair system, and/or to provide capacity to remodel thylakoid membranes in response to environmental cues, an important consideration given the extended life span of a plant compared to that of cyanobacteria.…”

Section: Discussionmentioning

confidence: 99%

Chloroplast vesicle transport

Lindquist

Aronsson

2018

Photosynth Res

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Photosynthesis is a well-known process that has been intensively investigated, but less is known about the biogenesis of the thylakoid membrane that harbors the photosynthetic machinery. Thylakoid membranes are constituted by several components, the major ones being proteins and lipids. However, neither of these two are produced in the thylakoid membranes themselves but are targeted there by different mechanisms. The interior of the chloroplast, the stroma, is an aqueous compartment that prevents spontaneous transport of single lipids and/or membrane proteins due to their hydrophobicities. Thylakoid targeted proteins are encoded either in the nucleus or plastid, and thus some cross the envelope membrane before entering one of the identified thylakoid targeting pathways. However, the pathway for all thylakoid proteins is not known. Lipids are produced at the envelope membrane and have been proposed to reach the thylakoid membrane by different means: invaginations of the envelope membrane, direct contact sites between these membranes, or through vesicles. Vesicles have been observed in chloroplasts but not much is yet known about the mechanism or regulation of their formation. The question of whether proteins can also make use of vesicles as one mechanism of transport remains to be answered. Here we discuss the presence of vesicles in chloroplasts and their potential role in transporting lipids and proteins. We additionally discuss what is known about the proteins involved in the vesicle transport and the gaps in knowledge that remain to be filled.

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Section: Discussionmentioning

confidence: 99%

Chloroplast vesicle transport

Lindquist

Aronsson

2018

Photosynth Res

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“…The evidence indicates that LHCP precursors achieve location and topology as they are guided by the transit sequence through translocons on the outer and inner envelope membranes. The transit sequence is removed soon after the N-terminal domain gains access to the stroma (Soll and Schleiff 2004 ; Vothknecht and Soll 2006 ). Membrane-spanning, nonpolar sequences that serve as stop-transfer domains are minimally 14–16 amino acids in length (Davis and Model 1985 ; Adams and Rose 1985 ; Popot and Engelman 2000 ).…”

Section: Model Of Lhcii Assemblymentioning

confidence: 99%

Chlorophylls, ligands and assembly of light-harvesting complexes in chloroplasts

2007

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Chlorophyll (Chl) b serves an essential function in accumulation of light-harvesting complexes (LHCs) in plants. In this article, this role of Chl b is explored by considering the properties of Chls and the ligands with which they interact in the complexes. The overall properties of the Chls, not only their spectral features, are altered as consequences of chemical modifications on the periphery of the molecules. Important modifications are introduction of oxygen atoms at specific locations and reduction or desaturation of sidechains. These modifications influence formation of coordination bonds by which the central Mg atom, the Lewis acid, of Chl molecules interacts with amino acid sidechains, as the Lewis base, in proteins. Chl a is a versatile Lewis acid and interacts principally with imidazole groups but also with sidechain amides and water. The 7-formyl group on Chl b withdraws electron density toward the periphery of the molecule and consequently the positive Mg is less shielded by the molecular electron cloud than in Chl a. Chl b thus tends to form electrostatic bonds with Lewis bases with a fixed dipole, such as water and, in particular, peptide backbone carbonyl groups. The coordination bonds are enhanced by H-bonds between the protein and the 7-formyl group. These additional strong interactions with Chl b are necessary to achieve assembly of stable LHCs.

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