Go your own way: membrane-targeting sequences

Abstract

Membrane-targeting sequences, connected targeting mechanisms, and co-factors orchestrate primary targeting of proteins to membranes.

Engineered Accumulation of Bicarbonate in Plant Chloroplasts: Known Knowns and Known Unknowns

“…While changing lipid composition to control orientation is unrealistic in plants (but was achieved in bacteria; Dowhan et al, 2019), rational design of TMDs, and interconnecting loops (Rapp et al, 2007) from HCO 3 − uptake systems might be an option. As shown for the secretory pathway in plant endoplasmic reticulum, membrane protein signal peptides may also play a role in the orientation of some proteins (Wojcik and Kriechbaumer, 2021). Hence, it is reasonable to assume that correct targeting and orientation of membrane proteins in the chloroplast IEM are dependent on both the cargo protein and its targeting sequence (Rolland et al, 2016;Uehara et al, 2016Uehara et al, , 2020.…”

“…Proteins translated in the cytosol and destined for the chloroplast either remain unfolded with the help of chaperones ( Jarvis, 2008 ), or can be imported to the chloroplast in a fully-formed state ( Ganesan et al, 2018 ), prior to translocation across the chloroplast envelope. These chaperones are crucial to prevent the premature folding of large proteins and aggregation and/or degradation of pre-proteins ( Wojcik and Kriechbaumer, 2021 ).…”

“…Correct targeting to the chloroplast membranes is further complicated by the presence of additional organelles in plant cells, and dual targeting between chloroplasts and mitochondria is commonly observed ( Peeters and Small, 2001 ; Sharma et al, 2018 ). This complexity of organelle targeting ( Bruce, 2000 ; Wojcik and Kriechbaumer, 2021 ) requires specific choice of cTP in proposed photosynthetic engineering strategies, and we suggest that the direction of foreign proteins to the appropriate cellular compartment is unlikely to be a one-size-fits-all solution ( Rolland et al, 2017 ). There are also likely to be protein cargo-specific requirements which determine the choice of cTP for each heterologous membrane protein directed to the chloroplast IEM, thus identifying the need to test and tailor genetic constructs on an individual basis.…”

An Interplay between Mitochondrial and ER Targeting of a Bacterial Signal Peptide in Plants

“…Proteins targeted to chloroplasts, mitochondria, peroxisomes and the nucleus generally do not follow the co-translational pathway to the ER and instead are targeted post-translationally from the cytosol to the respective organelles [ 11 ]. N-terminal targeting sequences with specific characteristics, such as the transit peptide, pre-sequence, peroxisomal targeting sequence, and nuclear localisation signal, determine the sorting of proteins to the chloroplast, mitochondria, peroxisome and nucleus, respectively [ 11 ]. Targeting sequences have low primary sequence conservation and are, therefore, predicted based on their physicochemical properties or tested empirically [ 12 , 13 ].…”

“…For example, a number of chloroplast proteins are targeted to the plastid via the ER and Golgi bodies [ 18 ]. Some peroxisomal membrane proteins are also targeted via an ER-derived compartment [ 11 ]. Mitochondrial proteins targeted via the ER have not been reported in plants.…”