Cellular and Molecular Life Sciences
Protein transport across and into cell membranes in bacteria and archaea
Jijun Yuan • Jessica C. Zweers • Jan Maarten van Dijl Ross E. Dalbey
Received: 16 June 2009 / Revised: 13 September 2009 / Accepted: 21 September 2009 / Published online: 10 October 2009 ¨ ÓBirkhauser Verlag, Basel/Switzerland 2009
Abstract In the three domains of life, the Sec, YidC/ Oxa1, and Tat translocases play important roles in protein translocation across membranes and membrane protein insertion. While extensive studies have been performed on the endoplasmic reticular and Escherichia coli systems, far fewer studies have been done on archaea, other Gramnegative bacteria, andGram-positive bacteria. Interestingly, work carried out to date has shown that there are differences in the protein transport systems in terms of the number of translocase components and, in some cases, the translocation mechanisms and energy sources that drive translocation. In this review, we will describe the different systems employed to translocate and insert proteins across or into thecytoplasmic membrane of archaea and bacteria. Keywords Archaea Á Gram-positive Á SecYEG Á Tat Á YidC Introduction All living cells are compartmentalized, irrespective of whether they belong to the eukaryotic, prokaryotic, or
J. Yuan and J. C. Zweers contributed equally to this work. J. Yuan Á R. E. Dalbey (&) Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, OH 43210, USAe-mail: firstname.lastname@example.org J. C. Zweers Á J. M. van Dijl (&) Department of Medical Microbiology, University Medical Center Groningen and University of Groningen, Hanzeplein 1, 30001, 9700 RB Groningen, The Netherlands e-mail: J.M.van.Dijl@med.umcg.nl
archaeal domains of life. The most complex cells are found in eukaryotes, and these contain a number of membranebound organelles,such as the endoplasmic reticulum (ER), nucleus, mitochondrion, peroxisome, golgi, nucleus, and lysosome. In total, there are over ten aqueous compartments and ten membrane subcellular locations in eukaryotic cells, each containing a unique set of proteins. Cells of bacteria and archaea are relatively simpler, with fewer aqueous compartments and intracellular membranes. Gram-negative bacteriacontain at least four subcellular locations (cytoplasm, inner membrane, periplasm, and outer membrane), while Gram-positive bacteria and archaea each contain at least three subcellular locations (cytoplasm, membrane, and cell wall). Proteins are sorted to their correct intracellular destinations or the extracellular space from their site of synthesis, which is typically in the cytoplasm. This processcan be very complex, as in the case of a chloroplast protein localized to the thylakoid lumen, which involves protein import into the chloroplast across the outer and inner membranes, followed by translocation across the internal thylakoid membrane. Approximately 25% of all proteins in a cell must cross at least one membrane to be properly localized, and roughly 20–25% of all proteins are membraneproteins that must insert into the lipid bilayer. Archaea, bacteria, and eukaryotes possess specialized translocases and insertases that catalyze the translocation of proteins into the membrane. The Sec machinery operates to insert proteins into the ER of eukaryotes and into the cytoplasmic membrane (plasma membrane) of bacteria and archaea, but it cannot translocate folded substrates across themembrane. In contrast, the Tat (twin-arginine translocation) system functions to translocate folded proteins across the cytoplasmic membrane in bacteria and archaea
J. Yuan et al.
as well as across the chloroplast thylakoid membrane in eukaryotes. The YidC/Oxa1 insertase inserts proteins into the membrane in mitochondria, chloroplasts, bacteria and, possibly, certain archaea. Whereas...