Search results for: Steven M. Theg

Items from 1 to 19 out of 19 results

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Structural considerations of folded protein import through the chloroplast TOC/TIC translocons

Iniyan Ganesan, Steven M. Theg

Protein import into chloroplasts is carried out by the protein translocons at the outer and inner envelope membranes (TOC and TIC). Detailed structures for these translocons are lacking, with only a low‐resolution TOC complex structure available. Recently, we showed that the TOC/TIC translocons can import folded proteins, a rather unique feat for a coupled double membrane system. We also determined...

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Chloroplast transport and import

Steven M. Theg

Photosynthesis Research > 2018 > 138 > 3 > 261-262

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Evolution of protein transport to the chloroplast envelope membranes

Philip M. Day, Steven M. Theg

Photosynthesis Research > 2018 > 138 > 3 > 315-326

Chloroplasts are descendants of an ancient endosymbiotic cyanobacterium that lived inside a eukaryotic cell. They inherited the prokaryotic double membrane envelope from cyanobacteria. This envelope contains prokaryotic protein sorting machineries including a Sec translocase and relatives of the central component of the bacterial outer membrane β-barrel assembly module. As the endosymbiont was integrated...

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A new fluorescence-based method to monitor the pH in the thylakoid lumen using GFP variants

Hong Yang, Xiaojun Pu, Lu Wang, Li Liu, more

Biochemical and Biophysical Research Communications > 2017 > 486 > 1 > 1-5

The ΔpH-dependent/Tat pathway is unique for using only the proton motive force for driving proteins transport across the thylakoid membrane in chloroplasts. 9-aminoacridine fluorescence quenching is widely used to monitor the ΔpH developed across the thylakoid membrane in the light. However, this method suffers from limited sensitivity to low ΔpH values and to spurious fluorescence signals due to...

chapter

Protein Transport and Post-translational Processing in Photosystem II Biosynthesis and Homeostasis

Steven M. Theg, Lan-Xin Shi

Advances in Photosynthesis and Respiration > Photosystem II > Assembly and Biodynamics of Photosystem II > 669-682

Summary The biogenesis, repair and homeostasis of Photosystem II (PS II) requires both protein targeting and post-translational modification. The various chloroplast targeting pathways for both nuclear-encoded and chloroplast-encoded proteins are described, with emphasis on the subunits of PS II. Also discussed are three post-translational processing events required for the development of PS II activity—removal...

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Photoheterotrophic growth of Physcomitrella patens

Terry M. Bricker, Adam J. Bell, Lan Tran, Laurie K. Frankel, more

Planta > 2014 > 239 > 3 > 605-613

Physcomitrella patens is a model bryophyte representing an early land plant in the green plant lineage. This organism possesses many advantages as a model organism. Its genome has been sequenced, its predominant life cycle stage is the haploid gametophyte, it is readily transformable and it can integrate transformed DNA into its genome by homologous recombination. One limitation for the use of P. patens...

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The chloroplast protein import system: From algae to trees

Lan-Xin Shi, Steven M. Theg

BBA - Molecular Cell Research > 2013 > 1833 > 2 > 314-331

Chloroplasts are essential organelles in the cells of plants and algae. The functions of these specialized plastids are largely dependent on the ~3000 proteins residing in the organelle. Although chloroplasts are capable of a limited amount of semiautonomous protein synthesis – their genomes encode ~100 proteins – they must import more than 95% of their proteins after synthesis in the cytosol. Imported...

article

Role of Vesicle‐Inducing Protein in Plastids 1 in cpTat transport at the thylakoid

Shari M. Lo, Steven M. Theg

The Plant Journal > 71 > 4 > 656 - 668

VIPP1 has been shown to be required for the proper formation of thylakoid membranes. However, studies on VIPP1 itself, as well as on PspA, its bacterial homolog, suggests that this protein may be involved in a number of additional functions, including protein translocation. The role of VIPP1 in protein translocation in the chloroplast has not been investigated. To this end, we conducted in vitro thylakoid...

article

The Chloroplast Tat Pathway Utilizes the Transmembrane Electric Potential as an Energy Source

Nikolai A. Braun, Andrew W. Davis, Steven M. Theg

Biophysical Journal > 2007 > 93 > 6 > 1993-1998

The thylakoid membrane, located inside the chloroplast, requires proteins transported across it for plastid biogenesis and functional photosynthetic electron transport. The chloroplast Tat translocator found on thylakoids transports proteins from the plastid stroma to the thylakoid lumen. Previous studies have shown that the chloroplast Tat pathway is independent of NTP hydrolysis as an energy source...

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Evidence for an ER to Golgi to chloroplast protein transport pathway

Resmi N. Radhamony, Steven M. Theg

Trends in Cell Biology > 2006 > 16 > 8 > 385-387

Chloroplast protein import is generally believed to occur posttranslationally through the interaction of a precursor protein with the Toc and Tic transport apparatus in the plastid envelope membranes. The cleavable N-terminal transit peptide present on translocated proteins has been considered to be essential and sufficient for targeting. This idea was recently challenged when an analysis of the chloroplast...

article

Methodological differences account for different conclusions regarding protein and energy requirements for chloroplast outer membrane protein targeting

Nancy R. Hofmann, Steven M. Theg

Trends in Plant Science > 2005 > 10 > 9 > 450-457

Proteins in the chloroplast outer envelope membrane are nuclear encoded and post-translationally targeted to the chloroplast. The targeting and membrane insertion of these proteins is not well understood. Although early work suggested otherwise, the best-studied outer membrane proteins (OMPs) use both proteins within the chloroplast and NTPs for insertion. There have been conflicting reports in the...

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The energetics of the chloroplast Tat protein transport pathway revisited

Steven M. Theg, Kenneth Cline, Giovanni Finazzi, Francis-André Wollman

Trends in Plant Science > 2005 > 10 > 4 > 153-154

article

Energy use by biological protein transport pathways

Nathan N. Alder, Steven M. Theg

Trends in Biochemical Sciences > 2003 > 28 > 8 > 442-451

The targeting of proteins into and across biological membranes to their correct cellular locations is mediated by a variety of transport pathways. These systems must couple the thermodynamically unfavorable processes of substrate translocation and integration with the expenditure of metabolic energy, using the free energy of ATP and GTP hydrolysis and/or a transmembrane protonmotive force. Several...

article

Protein transport via the cpTat pathway displays cooperativity and is stimulated by transport-incompetent substrate

Natahan N Alder, Steven M Theg

FEBS Letters > 2003 > 540 > 1-3 > 96-100

Kinetic analyses of cpTat-mediated protein transport across the thylakoid membrane were conducted, revealing three important characteristics of this translocation pathway. First, transport via the cpTAT system displays a non-Michaelis-Menten, sigmoidal rate-substrate relationship with an apparent Hill coefficient of 1.80, indicative of positive homotropic cooperativity. Second, the presence of transport-incompetent...

article

Energetics of Protein Transport across Biological Membranes - A Study of the Thylakoid ΔpH-Dependent/cpTat Pathway

Nathan N. Alder, Steven M. Theg

Cell > 2003 > 112 > 2 > 231-242

Among the pathways for protein translocation across biological membranes, the ΔpH-dependent/Tat system is unusual in its sole reliance upon the transmembrane pH gradient to drive protein transport. The free energy cost of protein translocation via the chloro-plast ΔpH-dependent/Tat pathway was measured by conducting in vitro transport assays with isolated thylakoids while concurrently monitoring energetic...

article

Physcomitrella patens as a model for the study of chloroplast protein transport: conserved machineries between vascular and non-vascular plants

Nancy Rosenbaum Hofmann, Steven M. Theg

Plant Molecular Biology > 2003 > 53 > 5 > 643-654

A single general import pathway in vascular plants mediates the transport of precursor proteins across the two membranes of the chloroplast envelope, and at least four pathways are responsible for thylakoid protein targeting. While the transport systems in the thylakoid are related to bacterial secretion systems, the envelope machinery is thought to have arisen with the endosymbiotic event and to...

article

Chemical Modification of Amine Groups on PS II Protein(s) Retards Photoassembly of the Photosynthetic Water-Oxidizing Complex ^†

Yasuo Ishikawa, Yasusi Yamamoto, Mayuko Otsubo, Steven M. Theg, more

Biochemistry > 2002 > 41 > 6 > 1972 - 1980

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Unassembled subunits of the photosynthetic oxygen-evolving complex present in the thylakoid lumen are long-lived and assembly-competent

Akiko Hashimoto, Yasusi Yamamoto, Steven M. Theg

FEBS Letters > 1996 > 391 > 1-2 > 29-34

Physiologically healthy pea chloroplasts contain unassembled, soluble subunits of the oxygen-evolving complex in the thylakoid lumen. We report that the lifetimes of two of these subunits, both on and off the membrane, exceed 8 h in vitro. We also demonstrate that each of the subunits present in the thylakoid lumen is competent for assembly into the membrane-bound complex. These data are consistent...