%0 Journal Article
%T Assembly of the ¦Â-Barrel Outer Membrane Proteins in Gram-Negative Bacteria, Mitochondria, and Chloroplasts
%A Rajeev Misra
%J ISRN Molecular Biology
%D 2012
%R 10.5402/2012/708203
%X In the last decade, there has been an explosion of publications on the assembly of ¦Â-barrel outer membrane proteins (OMPs), which carry out diverse cellular functions, including solute transport, protein secretion, and assembly of protein and lipid components of the outer membrane. Of the three outer membrane model systems¡ªGram-negative bacteria, mitochondria and chloroplasts¡ªresearch on bacterial and mitochondrial systems has so far led the way in dissecting the ¦Â-barrel OMP assembly pathways. Many exciting discoveries have been made, including the identification of ¦Â-barrel OMP assembly machineries in bacteria and mitochondria, and potentially the core assembly component in chloroplasts. The atomic structures of all five components of the bacterial ¦Â-barrel assembly machinery (BAM) complex, except the ¦Â-barrel domain of the core BamA protein, have been solved. Structures reveal that these proteins contain domains/motifs known to facilitate protein-protein interactions, which are at the heart of the assembly pathways. While structural information has been valuable, most of our current understanding of the ¦Â-barrel OMP assembly pathways has come from genetic, molecular biology, and biochemical analyses. This paper provides a comparative account of the ¦Â-barrel OMP assembly pathways in Gram-negative bacteria, mitochondria, and chloroplasts. 1. Introduction The outer membrane encircles Gram-negative bacteria, mitochondria, and chloroplasts. Embedded within this membrane is a unique class of proteins that fold into a ¦Â-barrel structure consisting of 8 to 22 antiparallel ¦Â-strands, interacting through hydrogen bonding to the neighboring strands, with the first strand being frequently hydrogen bonded to the last strand. Atomic structures of an impressive number of the ¦Â-barrel outer membrane proteins (OMPs) have been solved [1]. In general, the nonpolar side chains of a folded ¦Â-barrel are oriented outwardly towards the lipid bilayer of the membrane, while the polar side chains are exposed inwardly towards the interior of the barrel that often forms a channel. The two main activities of the ¦Â-barrel OMPs are to permit transport/insertion of proteins and diffusion of solutes across the outer membrane. The latter class of proteins is called porin [2]. These fundamental activities make the outer membrane an immensely important cellular structure of Gram-negative bacteria and eukaryotes. In Gram-negative bacteria, the assembly and insertion of porin and non-porin proteins are catalyzed by the ¦Â-barrel assembly machinery (BAM) [3¨C6]. The BAM complex also assists
%U http://www.hindawi.com/journals/isrn.molecular.biology/2012/708203/