共查询到20条相似文献,搜索用时 171 毫秒
1.
Kleinschmidt JH 《Cellular and molecular life sciences : CMLS》2003,60(8):1547-1558
The biophysical principles and mechanisms by which membrane proteins insert and fold into a biomembrane have mostly been studied with bacteriorhodopsin and outer membrane protein A (OmpA). This review describes the assembly process of the monomeric outer membrane proteins of Gram-negative bacteria, for which OmpA has served as an example. OmpA is a two-domain outer membrane protein composed of a 171-residue eight-stranded -barrel transmembrane domain and a 154-residue periplasmic domain. OmpA is translocated in an unstructured form across the cytoplasmic membrane into the periplasm. In the periplasm, unfolded OmpA is kept in solution in complex with the molecular chaperone Skp. After binding of periplasmic lipopolysaccharide, OmpA insertion and folding occur spontaneously upon interaction of the complex with the phospholipid bilayer. Insertion and folding of the -barrel transmembrane domain into the lipid bilayer are highly synchronized, i.e. the formation of large amounts of -sheet secondary structure and -barrel tertiary structure take place in parallel with the same rate constants, while OmpA inserts into the hydrophobic core of the membrane. In vitro, OmpA can successfully fold into a range of model membranes of very different phospholipid compositions, i.e. into bilayers of lipids of different headgroup structures and hydrophobic chain lengths. Three membrane-bound folding intermediates of OmpA were discovered in folding studies with dioleoylphosphatidylcholine bilayers. Their formation was monitored by time-resolved distance determinations by fluorescence quenching, and they were structurally distinguished by the relative positions of the five tryptophan residues of OmpA in projection to the membrane normal. Recent studies indicate a chaperone-assisted, highly synchronized mechanism of secondary and tertiary structure formation upon membrane insertion of -barrel membrane proteins such as OmpA that involves at least three structurally distinct folding intermediates. 相似文献
2.
All cells must traffic proteins into and across their membranes. In bacteria, several pathways have evolved to enable protein
transfer across the inner membrane, the periplasm, and the outer membrane. The major route of protein translocation in and
across the cytoplasmic membrane is the general secretion pathway (Sec-pathway). The biogenesis of membrane proteins not only
requires protein translocation but also coordinated targeting to the membrane beforehand and folding and assembly into their
protein complexes afterwards to function properly in the cell. All these processes are responsible for the biogenesis of membrane
proteins that mediate essential functions of the cell such as selective transport, energy conversion, cell division, extracellular
signal sensing, and motility. This review will highlight the most recent developments on the structure and function of bacterial
membrane proteins, focusing on the journey that integral membrane proteins take to find their final destination in the inner
membrane. 相似文献
3.
Biogenesis of mitochondrial porin: the import pathway. 总被引:2,自引:0,他引:2
We review here the present knowledge about the pathway of import and assembly of porin into mitochondria and compare it to those of other mitochondrial proteins. Porin, like all outer mitochondrial membrane proteins studied so far is made as a precursor without a cleavable 'signal' sequence; thus targeting information must reside in the mature sequence. At least part of this information appears to be located at the amino-terminal end of the molecule. Transport into mitochondria can occur post-translationally. In a first step, the porin precursor is specifically recognized on the mitochondrial surface by a protease sensitive receptor. In a second step, porin precursor inserts partially into the outer membrane. This step is mediated by a component of the import machinery common to the import pathways of precursor proteins destined for other mitochondrial subcompartments. Finally, porin is assembled to produce the functional oligomeric form of an integral membrane protein which is characterized by its extreme protease resistance. 相似文献
4.
The biogenesis and function of eukaryotic porins. 总被引:2,自引:0,他引:2
M Dihanich 《Experientia》1990,46(2):146-153
Like most other mitochondrial proteins porin is synthesized in the cytosol and imported posttranslationally into the outer mitochondrial membrane. This transport follows the general rules for mitochondrial protein import with a few aberrations: a) porin contains an uncleaved NH2-terminal signal sequence, b) also its carboxyterminus might be involved in the import process, and c) this transport does not seem to require a membrane potential delta psi, although it is ATP-dependent. Most likely the actual import step occurs at contact sites between the outer and the inner mitochondrial membrane and involves at least one receptor protein. Although porin is known to be the major gate through the outer mitochondrial membrane, its absence only causes transient respiratory problems in yeast cells. This could mean a) that there is a bypass for some mitochondrial functions in the cytosol and/or b) that there are alternative channel proteins in the outer membrane. The first idea is supported by the overexpression of cytosolic virus-like particles in yeast cells lacking porin and the second by the occurrence of residual pore activity in mitochondrial outer membrane purified from porinless mutant cells. 相似文献
5.
C Marchal D Perrin M Hofnung 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,288(2):275-277
We describe a method which should allow construction of bacterial strains able to export a given protein through the cytoplasmic membrane. The principle is to fuse the structural gene of the protein to the proximal part of gene lamB, the structural gene of the lambda receptor, an outer membrane protein of E. coli K-12. 相似文献
6.
Summary We review here the present knowledge about the pathway of import and assembly of porin into mitochondria and compare it to those of other mitochondrial proteins. Porin, like all outer mitochondrial membrane proteins studied so far is made as a precursor without a cleavble signal sequence; thus targeting information must reside in the mature sequence. At least part of this information appears to be located at the amino-terminal end of the molecule. Transport into mitochondria can occur post-translationally. In a first step, the porin precursor is specifically recognized on the mitochondrial surface by a protease sensitive receptor. In a second step, porin precursor inserts partially into the outer membrane. This step is mediated by a component of the import machinery common to the import pathways of precursor proteins destined for other mitochondrial subcompartments. Finally, porin is assembled to produce the functional oligomeric form of an integral membrane protein wich is characterized by its extreme protease resistance. 相似文献
7.
M. Dihanich 《Cellular and molecular life sciences : CMLS》1990,46(2):146-153
Summary Like most other mitochondrial proteins porin is synthesized in the cytosol and imported posttranslationally into the outer mitochondrial membrane. This transport follows the general rules for mitochondrial, protein import with a few aberrations: a) porin contains an,uncleaved NH2-terminal signal sequence, b) also its carboxyterminus might be involved in the import process, and c) this transport does not seem to require a membrane potential , although it is ATP-dependent. Most likely the actual import step occurs at contact sites between the outer and the inner mitochondrial membrane and involved at least one receptor protein.Although porin is known to be the major gate through the outer mitochondrial membrane, its absence only causes transient respiratory problems in yeast cells. This could mean a) that there is a bypass for some mitochondrial functions in the cytosol and/or b) that there are alternative channel proteins in the outer membrane. The first idea is supported by the overexpression of cytosolic virus-like particles in yeast cells lacking porin and the second by the occurrence of residual pore activity in mitochondrial outer membrane purified from porinless mutant cells. 相似文献
8.
Izaurralde E 《Cellular and molecular life sciences : CMLS》2001,58(8):1105-1112
The distinguishing feature of eukaryotic cells is the segregation of RNA biogenesis and DNA replication in the nucleus, separate
from the cytoplasmic machinery for protein synthesis. As a consequence, messenger RNAs (mRNAs) and all cytoplasmic RNAs from
nuclear origin need to be transported from their site of synthesis in the nucleus to their final cytoplasmic destination.
Nuclear export occurs through nuclear pore complexes (NPCs) and is mediated by saturable transport receptors, which shuttle
between the nucleus and cytoplasm. The past years have seen great progress in the characterization of the mRNA export pathway
and the identification of proteins involved in this process. A novel family of nuclear export receptors (the NXF family),
distinct from the well-characterized family of importin β-like proteins, has been implicated in the export of mRNA to the cytoplasm.
Received 23 January 2001; received after revision 12 April 2001; accepted 12 April 2001 相似文献
9.
Gregory Jon Anderson Christopher D. Vulpe 《Cellular and molecular life sciences : CMLS》2009,66(20):3241-3261
Iron is essential for basic cellular processes but is toxic when present in excess. Consequently, iron transport into and
out of cells is tightly regulated. Most iron is delivered to cells bound to plasma transferrin via a process that involves
transferrin receptor 1, divalent metal-ion transporter 1 and several other proteins. Non-transferrin-bound iron can also be
taken up efficiently by cells, although the mechanism is poorly understood. Cells can divest themselves of iron via the iron
export protein ferroportin in conjunction with an iron oxidase. The linking of an oxidoreductase to a membrane permease is
a common theme in membrane iron transport. At the systemic level, iron transport is regulated by the liver-derived peptide
hepcidin which acts on ferroportin to control iron release to the plasma. 相似文献
10.
Ragg H 《Cellular and molecular life sciences : CMLS》2007,64(21):2763-2770
Serpins (serine protease inhibitors) constitute a class of proteins with an unusually wide spectrum of different functions at extracellular sites and within the nucleocytoplasmic compartment that extends from protease inhibition to hormone transport and regulation of chromatin organization. Recent investigations reveal a growing number of serpins acting in secretory pathway organelles, indicating that they are not simply cargo destined for export, but fulfill distinct roles within the classical organelle-coupled trafficking system. These findings imply that some serpins are part of a quality control system that monitors the export and possibly import routes of eukaryotic cells. The molecular targets of these serpins are often unknown, opening new avenues for future research. 相似文献
11.
Despite being relatively insensitive to environmental insult, the spore is responsive to low concentrations of chemical germinants,
which induce germination. The process of bacterial spore germination involves membrane permeability changes, ion fluxes and
the activation of enzymes that degrade the outer layers of the spore. A number of components in the spore that are required
for the germination response have been identified, including a spore-specific family of receptor proteins (the GerA family),
an ion transporter and cortex lytic enzymes. The germinant traverses the outer layers of the spore and interacts with its
receptor in the inner membrane to initiate the cascade of germination events, but the molecular details of this signal transduction
process remain to be identified. 相似文献
12.
Recent work has led to significant advances in our understanding of the late steps of genetic recombination and the post-replicational repair of DNA. The RuvA and RuvB proteins have been shown to interact with recombination intermediates and catalyse the branch migration of Holliday junctions. Although both proteins are required for branch migration, each plays a defined role with RuvA acting as a specificity factor that directs RuvB (an ATPase) to the junction. The RuvB ATPase provides the motor for branch migration. The next step is catalysed by RuvC protein which recognises Holliday junctions and promotes their resolution by endonucleolytic cleavage. New data indicates an alternative pathway for Holliday junction processing. This pathway involves RecG, a branch migration protein which is functionally analogous to RuvAB, and a protein (activated by arus mutation) which works with RecG to process intermediates independently of RuvA, RuvB and RuvC. 相似文献
13.
Jean-Pierre Vilardaga Guillermo Romero Peter A. Friedman Thomas J. Gardella 《Cellular and molecular life sciences : CMLS》2011,68(1):1-13
The parathyroid hormone (PTH) receptor type 1 (PTHR), a G protein-coupled receptor (GPCR), transmits signals to two hormone
systems—PTH, endocrine and homeostatic, and PTH-related peptide (PTHrP), paracrine—to regulate different biological processes.
PTHR responds to these hormonal stimuli by activating heterotrimeric G proteins, such as GS that stimulates cAMP production. It was thought that the PTHR, as for all other GPCRs, is only active and signals through
G proteins on the cell membrane, and internalizes into a cell to be desensitized and eventually degraded or recycled. Recent
studies with cultured cell and animal models reveal a new pathway that involves sustained cAMP signaling from intracellular
domains. Not only do these studies challenge the paradigm that cAMP production triggered by activated GPCRs originates exclusively
at the cell membrane but they also advance a comprehensive model to account for the functional differences between PTH and
PTHrP acting through the same receptor. 相似文献
14.
Harald W. Platta Stefanie Hagen Ralf Erdmann 《Cellular and molecular life sciences : CMLS》2013,70(8):1393-1411
Peroxisomes constitute a dynamic compartment of almost all eukaryotic cells. Depending on environmental changes and cellular demands peroxisomes can acquire diverse metabolic roles. The compartmentalization of peroxisomal matrix enzymes is a prerequisite to carry out their physiologic function. The matrix proteins are synthesized on free ribosomes in the cytosol and are ferried to the peroxisomal membrane by specific soluble receptors. Subsequent to cargo release into the peroxisomal matrix, the receptors are exported back to the cytosol to facilitate further rounds of matrix protein import. This dislocation step is accomplished by a remarkable machinery, which comprises enzymes required for the ubiquitination as well as the ATP-dependent extraction of the receptor from the membrane. Interestingly, receptor ubiquitination and dislocation are the only known energy-dependent steps in the peroxisomal matrix protein import process. The current view is that the export machinery of the receptors might function as molecular motor not only in the dislocation of the receptors but also in the import step of peroxisomal matrix protein by coupling ATP-dependent removal of the peroxisomal import receptor with cargo translocation into the organelle. In this review we will focus on the architecture and function of the peroxisomal receptor export machinery, the peroxisomal exportomer. 相似文献
15.
A dynamic view of peptides and proteins in membranes 总被引:1,自引:0,他引:1
Bechinger B 《Cellular and molecular life sciences : CMLS》2008,65(19):3028-3039
Biological membranes are highly dynamic supramolecular arrangements of lipids and proteins, which fulfill key cellular functions.
Relatively few high-resolution membrane protein structures are known to date, although during recent years the structural
databases have expanded at an accelerated pace. In some instances the structures of reaction intermediates provide a stroboscopic
view on the conformational changes involved in protein function. Other biophysical approaches add dynamic aspects and allow
one to investigate the interactions with the lipid bilayers. Membrane-active peptides fulfill many important functions in
nature as they act as antimicrobials, channels, transporters or hormones, and their studies have much increased our understanding
of polypeptide-membrane interactions. Interestingly several proteins have been identified that interact with the membrane
as loose arrays of domains. Such conformations easily escape classical high-resolution structural analysis and the lessons
learned from peptides may therefore be instructive for our understanding of the functioning of such membrane proteins.
Received 11 March 2008; received after revision 2 May 2008; accepted 5 May 2008 相似文献
16.
Basañez G 《Cellular and molecular life sciences : CMLS》2002,59(9):1478-1490
Membrane fusion constitutes a pivotal process in eukaryotic cell physiology. Both specialized proteins and membrane lipids
play key roles in fusion. Here, our current understanding of the mechanism of membrane fusion is reviewed. The focus is on
the relatively simple and well-understood proteinaceous fusion machinery of enveloped viruses and the physical properties
of lipids that appear to be of great relevance for fusion progression. Recent observations suggest that viral fusion proteins
use packed conformational energy and bilayer-destabilizing domains to (i) bring participating membranes into intimate contact,
(ii) merge proximal lipid monolayers through highly curved stalk/hemifusion intermediates, and (iii) generate a lipid-containing
fusion pore, thereby terminating the fusion process.
Received 4 January 2002; received after revision 3 April 2002; accepted 5 April 2002 相似文献
17.
Lu W Schneider M Neumann S Jaeger VM Taranum S Munck M Cartwright S Richardson C Carthew J Noh K Goldberg M Noegel AA Karakesisoglou I 《Cellular and molecular life sciences : CMLS》2012,69(20):3493-3509
Nesprins-1/-2/-3/-4 are nuclear envelope proteins, which connect nuclei to the cytoskeleton. The largest nesprin-1/-2 isoforms (termed giant) tether F-actin through their N-terminal actin binding domain (ABD). Nesprin-3, however, lacks an ABD and associates instead to plectin, which binds intermediate filaments. Nesprins are integrated into the outer nuclear membrane via their C-terminal KASH-domain. Here, we show that nesprin-1/-2 ABDs physically and functionally interact with nesprin-3. Thus, both ends of nesprin-1/-2 giant are integrated at the nuclear surface: via the C-terminal KASH-domain and the N-terminal ABD-nesprin-3 association. Interestingly, nesprin-2 ABD or KASH-domain overexpression leads to increased nuclear areas. Conversely, nesprin-2 mini (contains the ABD and KASH-domain but lacks the massive nesprin-2 giant rod segment) expression yields smaller nuclei. Nuclear shrinkage is further enhanced upon nesprin-3 co-expression or microfilament depolymerization. Our findings suggest that multivariate intermolecular nesprin interactions with the cytoskeleton form a lattice-like filamentous network covering the outer nuclear membrane, which determines nuclear size. 相似文献
18.
The ATP-binding cassette family is one of the largest groupings of membrane proteins, moving allocrites across lipid membranes,
using energy from ATP. In bacteria, they reside in the inner membrane and are involved in both uptake and export. In eukaryotes,
these transporters reside in the cell’s internal membranes as well as in the plasma membrane and are unidirectional—out of
the cytoplasm. The range of substances that these proteins can transport is huge, which makes them interesting for structure–function
studies. Moreover, their abundance in nature has made them targets for structural proteomics consortia. There are eight independent
structures for ATP-binding cassette transporters, making this one of the best characterised membrane protein families. Our
understanding of the mechanism of transport across membranes and membrane protein structure in general has been enhanced by
recent developments for this family. 相似文献
19.
R Benz 《Experientia》1990,46(2):131-137
The matrix space of mitochondria is surrounded by two membranes. The mitochondrial inner membrane contains the respiration chain and a large number of highly specific carriers for the mostly anionic substrates of mitochondrial metabolism. In contrast to this the permeability properties of the mitochondrial outer membrane are by far less specific. It acts as a molecular sieve for hydrophilic molecules with a defined exclusion limit around 3000 Da. Responsible for the extremely high permeability of the mitochondrial outer membrane is the presence of a pore-forming protein termed mitochondrial porin. Mitochondrial porins have been isolated from a variety of eukaryotic cells. They are basic proteins with molecular masses between 30 and 35 kDa. Reconstitution experiments define their function as pore-forming components with a single-channel conductance of about 0.40 nS (nano Siemens) in 0.1 M KCl at low voltages. In the open state mitochondrial porin behaves as a general diffusion pore with an effective diameter of 1.7 nm. Eukaryotic porins are slightly anion-selective in the open state but become cation-selective after voltage-dependent closure. 相似文献
20.
R. Benz 《Cellular and molecular life sciences : CMLS》1990,46(2):131-137
Summary The matrix space of mitochondria is surrounded by two membranes. The mitochondrial inner membrane contains the respiration chain and a large number of highly specific carriers for the mostly anionic substrates of mitochondrial metabolism. In contrast to this the permeability properties of the mitochondrial outer membrane are by far less specific. It acts as a molecular sieve for hydrophilic molecules with a defined exclusion limit around 3000 Da. Responsible for the extremely high permeability of the mitochondrial outer membrane is the presence of a pore-forming protein termed mitochondrial porin. Mitochondrial porins have been isolated from a variety of eukaryotic cells. They are basic proteins with molecular masses between 30 and 35 kDa. Reconstitution experiments define their function as pore-forming components with a single-channel conductance of about 0.40 nS (nano Siemens) in 0.1 M KCl at low voltages. In the open state mitochondrial porin behaves as a general diffusion pore with an effective diameter of 1.7 nm. Eukaryotic porins are slightly anion-selective in the open state but become cation-selective after voltage-dependent closure. 相似文献