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1.
Myelin basic protein: a multifunctional protein 总被引:1,自引:1,他引:0
Boggs JM 《Cellular and molecular life sciences : CMLS》2006,63(17):1945-1961
Myelin basic protein (MBP), the second most abundant protein in central nervous system myelin, is responsible for adhesion
of the cytosolic surfaces of multilayered compact myelin. A member of the ‘intrinsically disordered’ or conformationally adaptable
protein family, it also appears to have several other functions. It can interact with a number of polyanionic proteins including
actin, tubulin, Ca2+-calmodulin, and clathrin, and negatively charged lipids, and acquires structure on binding to them. It may act as a membrane
actin-binding protein, which might allow it to participate in transmission of extracellular signals to the cytoskeleton in
oligodendrocytes and tight junctions in myelin. Some size isoforms of MBP are transported into the nucleus and thus they may
also bind polynucleotides. Extracellular signals received by myelin or cultured oligodendrocytes cause changes in phosphorylation
of MBP, suggesting that MBP is also involved in signaling. Further study of this very abundant protein will reveal how it
is utilized by the oligodendrocyte and myelin for different purposes.
Received 2 March 2006; received after revision 12 April 2006; accepted 16 May 2006 相似文献
2.
3.
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
4.
Myelin sheaths: glycoproteins involved in their formation,maintenance and degeneration 总被引:8,自引:0,他引:8
Quarles RH 《Cellular and molecular life sciences : CMLS》2002,59(11):1851-1871
Myelin sheaths are formed around axons by extending, biochemically modifying and spiraling plasma membranes of Schwann cells
in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS). Because glycoproteins are
prominent components of plasma membranes, it is not surprising that they have important roles in the formation, maintenance
and degeneration of myelin sheaths. The emphasis in this review is on four integral membrane glycoproteins. Two of them, protein
zero (P0) and peripheral myelin protein-22 (PMP-22), are components of compact PNS myelin. The other two are preferentially
localized in membranes of sheaths that are distinct from compact myelin. One is the myelin-associated glycoprotein, which
is localized at the inside of sheaths where it functions in glia-axon interactions in both the PNS and CNS. The other is the
myelin-oligodendrocyte glycoprotein, which is preferentially localized on the outside of CNS myelin sheaths and appears to
be an important target antigen in autoimmune demyelinating diseases such as multiple sclerosis.
Received 8 April 2002; received after revision 13 May 2002; accepted 22 May 2002 相似文献
5.
The myelin proteolipid protein (PLP) gene (Plp) encodes the most abundant protein found in myelin from the central nervous system (CNS). Expression of the gene is regulated in a spatiotemporal manner with maximal levels of expression occurring in oligodendrocytes during the active myelination period of CNS development, although other cell types in the CNS as well as in the periphery can express the gene to a much lower degree. In oligodendrocytes, Plp gene expression is tightly regulated. Underexpression or overexpression of the gene has been shown to have adverse effects in humans and other vertebrates. In light of this strict control, this review provides an overview of the current knowledge of Plp gene regulation.Received 4 August 2003; received after revision 17 September 2003; accepted 24 September 2003 相似文献
6.
Genetic and molecular analysis of the synaptotagmin family 总被引:5,自引:0,他引:5
Secretion is a fundamental cellular process used by all eukaryotes to insert proteins into the plasma membrane and transport
signaling molecules and intravesicular proteins into the extracellular space. Secretion requires the fusion of two phospholipid
bilayers within the cell, an energetically unfavorable process. A conserved repertoire of vesicle-trafficking proteins has
evolved that function to overcome this energy barrier and temporally and spatially control membrane fusion within the cell.
Within neurons, opening of synaptic calcium channels and subsequent calcium entry triggers synchronous synaptic vesicle exocytosis
and neurotransmitter release into the synaptic cleft. After fusion, synaptic vesicles undergo endocytosis, are refilled with
neurotransmitter, and return to the vesicle pool for further rounds of cycling. It is within this local synaptic trafficking
pathway that the synaptotagmin family of calcium-binding synaptic vesicle proteins has been postulated to function. Here we
review the current literature on the function of the synaptotagmin family and discuss the implications for synaptic transmission
and membrane trafficking.
Received 14 August 2000; received after revision 20 September 2000, accepted 14 October 2000 相似文献
7.
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
8.
Summary Measurements of the distribution of Na, P, Cl and K were performed in different structures of the myelinated nerve. Whereas the axon shows a typical intracellular distribution pattern for Na, Cl and K, the interstitial space and the myelin sheath show a typical extracellular pattern. These measurements have demonstrated that Na is present in the myelin sheath close to the node of Ranvier. 相似文献
9.
Measurements of the distribution of Na, P, Cl and K were performed in different structures of the myelinated nerve. Whereas the axon shows a typical intracellular distribution pattern for Na, Cl and K, the interstitial space and the myelin sheath show a typical extracellular pattern. These measurements have demonstrated that Na is present in the myelin sheath close to the node of Ranvier. 相似文献
10.
Robert Renthal 《Cellular and molecular life sciences : CMLS》2010,67(7):1077-1088
Polytopic α-helical membrane proteins cannot spontaneously insert into lipid bilayers without assistance from polytopic α-helical
membrane proteins that already reside in the membrane. This raises the question of how these proteins evolved. Our current
knowledge of the insertion of α-helices into natural and model membranes is reviewed with the goal of gaining insight into
the evolution of membrane proteins. Topics include: translocon-dependent membrane protein insertion, antibiotic peptides and
proteins, in vitro insertion of membrane proteins, chaperone-mediated insertion of transmembrane helices, and C-terminal tail-anchored
(TA) proteins. Analysis of the E. coli genome reveals several predicted C-terminal TA proteins that may be descendents of proteins involved in pre-cellular membrane
protein insertion. Mechanisms of pre-translocon polytopic α-helical membrane protein insertion are discussed. 相似文献
11.
Biological cells harbor a variety of molecular machines that carry out mechanical work at the nanoscale. One of these nanomachines
is the bacterial motor protein SecA which translocates secretory proteins through the protein-conducting membrane channel
SecYEG. SecA converts chemically stored energy in the form of ATP into a mechanical force to drive polypeptide transport through
SecYEG and across the cytoplasmic membrane. In order to accommodate a translocating polypeptide chain and to release transmembrane
segments of membrane proteins into the lipid bilayer, SecYEG needs to open its central channel and the lateral gate. Recent
crystal structures provide a detailed insight into the rearrangements required for channel opening. Here, we review our current
understanding of the mode of operation of the SecA motor protein in concert with the dynamic SecYEG channel. We conclude with
a new model for SecA-mediated protein translocation that unifies previous conflicting data. 相似文献
12.
Sei Yoshida Regina Pacitto Ken Inoki Joel Swanson 《Cellular and molecular life sciences : CMLS》2018,75(7):1227-1239
The growth and proliferation of metazoan cells are driven by cellular nutrient status and by extracellular growth factors. Growth factor receptors on cell surfaces initiate biochemical signals that increase anabolic metabolism and macropinocytosis, an actin-dependent endocytic process in which relatively large volumes of extracellular solutes and nutrients are internalized and delivered efficiently into lysosomes. Macropinocytosis is prominent in many kinds of cancer cells, and supports the growth of cells transformed by oncogenic K-Ras. Growth factor receptor signaling and the overall metabolic status of the cell are coordinated in the cytoplasm by the mechanistic target-of-rapamycin complex-1 (mTORC1), which positively regulates protein synthesis and negatively regulates molecular salvage pathways such as autophagy. mTORC1 is activated by two distinct Ras-related small GTPases, Rag and Rheb, which associate with lysosomal membranes inside the cell. Rag recruits mTORC1 to the lysosomal surface where Rheb directly binds to and activates mTORC1. Rag is activated by both lysosomal luminal and cytosolic amino acids; Rheb activation requires phosphoinositide 3-kinase, Akt, and the tuberous sclerosis complex-1/2. Signals for activation of Rag and Rheb converge at the lysosomal membrane, and several lines of evidence support the idea that growth factor-dependent endocytosis facilitates amino acid transfer into the lysosome leading to the activation of Rag. This review summarizes evidence that growth factor-stimulated macropinocytosis is essential for amino acid-dependent activation of mTORC1, and that increased solute accumulation by macropinocytosis in transformed cells supports unchecked cell growth. 相似文献
13.
Olfactory ensheathing cell phenotype following implantation in the lesioned spinal cord 总被引:5,自引:2,他引:3
Woodhall E West AK Vickers JC Chuah MI 《Cellular and molecular life sciences : CMLS》2003,60(10):2241-2253
14.
Marsh D 《Cellular and molecular life sciences : CMLS》2003,60(8):1575-1580
Magnetic resonance results, principally from 2H-nuclear magnetic resonance, indicate that the mean lipid-chain ordering at the surface of transmembrane proteins is comparable to that in fluid lipid bilayers. Principally, it is the requirement for matching the hydrophobic lengths of lipid and protein that modulates the degree of chain ordering at the lipid-protein interface. The distribution of chain order parameters is, nonetheless, broader in the presence of integral proteins than in fluid lipid bilayers. The chain configurations of the phospholipids that are resolved in crystals of integral membrane proteins display considerable conformational heterogeneity. Chain C–C dihedral angles are, however, not restricted to the energetically allowable trans and gauche rotamers. This indicates that the chains of a given lipid do not have a unique configuration in protein crystals. 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.
Summary The re-formed membranes prepared from butanol extracts of myelin were examined by morphological and biochemical methods. Using freeze-fracturing, re-formed membranes showed 2 types of assembly of membrane particles, i.e., myelin-like and cluster arrangements. Moreover, SDS-urea disc gel electrophoresis indicated that the protein composition of these membranes reflected that of the myelin fragments.Acknowledgment. This work was supported by a research grant (No. 467 384) from the Ministry of Education, Japan. 相似文献
17.
de Keyzer J van der Does C Driessen AJ 《Cellular and molecular life sciences : CMLS》2003,60(10):2034-2052
The major route of protein translocation in bacteria is the so-called general secretion pathway (Sec-pathway). This route has been extensively studied in Escherichia coli and other bacteria. The movement of preproteins across the cytoplasmic membrane is mediated by a multimeric membrane protein complex called translocase. The core of the translocase consists of a proteinaceous channel formed by an oligomeric assembly of the heterotrimeric membrane protein complex SecYEG and the peripheral adenosine triphosphatase (ATPase) SecA as molecular motor. Many secretory proteins utilize the molecular chaperone SecB for targeting and stabilization of the unfolded state prior to translocation, while most nascent inner membrane proteins are targeted to the translocase by the signal recognition particle and its membrane receptor. Translocation is driven by ATP hydrolysis and the proton motive force. In the last decade, genetic and biochemical studies have provided detailed insights into the mechanism of preprotein translocation. Recent crystallographic studies on SecA, SecB and the SecYEG complex now provide knowledge about the structural features of the translocation process. Here, we will discuss the mechanistic and structural basis of the translocation of proteins across and the integration of membrane proteins into the cytoplasmic membrane.Received 10 January 2003; received after revision 2 April 2003; accepted 4 April 2003 相似文献
18.
T Sasaki 《Experientia》1990,46(6):611-616
Glycolipid transfer protein (GL-TP), a nonglycosylated protein with a molecular weight of 22,000 K, has been purified from pig brain. The protein transfers, by a carrier mechanism, glycolipids with a beta-glucosyl or beta-galactosyl residue directly linked to either ceramide or diacylglycerol. GL-TP appears to be present in most animal cells, and evidence has been obtained which indicates that it is a cytoplasmic protein. Little is known about the function of GL-TP. Current evidence indicates that glycosphingolipid glycosylation occurs at the luminal side of the Golgi apparatus, except for the glucosylation of ceramide, which has been shown to occur at the cytoplasmic side of the Golgi or endoplasmic membrane. It appears most likely that GL-TP participates in the intracellular traffic of glucosylceramide. 相似文献
19.
P-glycoprotein (P-gp) is an active membrane transporter responsible for cell detoxification against numerous amphiphilic compounds,
leading to multidrug resistance in tumor cells. It displays entangled connections with its membrane environment since it recognizes
its substrates within the cytosolic leaflet and it also translocates some endogenous lipids to the exoplasmic leaflet. Regarding
its relationships with membrane microdomains, ‘lipid rafts’, a literature analysis concludes that (i) P-gp also exists in
rafts and non-raft membrane domains, depending on the cell considered, the experimental conditions and the method used to
test it; (ii) cholesterol has a positive influence on P-gp function, and this may be a direct effect of the free cholesterol
present in membrane or an indirect effect mediated by the cholesterol-enriched microdomains; (iii) when present in rafts,
P-gp interacts with protein partners regulating its activity; (iv) P-gp is a lipid translocase that handles the raft-constituting
lipids with particular efficiency, and it also influences membrane trafficking in the cell.
Received 18 November 2005; received after revision 23 December 2005; accepted 12 January 2006 相似文献
20.
Periostin is a matricellular protein that is composed of a multi-domain structure with an amino-terminal EMI domain, a tandem repeat of four FAS 1 domains, and a carboxyl-terminal domain. These distinct domains have been demonstrated to bind to many proteins including extracellular matrix proteins (Collagen type I and V, fibronectin, tenascin, and laminin), matricellular proteins (CCN3 and βig-h3), and enzymes that catalyze covalent crosslinking between extracellular matrix proteins (lysyl oxidase and BMP-1). Adjacent binding sites on periostin have been suggested to put the interacting proteins in close proximity, promoting intermolecular interactions between each protein, and leading to their assembly into extracellular architectures. These extracellular architectures determine the mechanochemical properties of connective tissues, in which periostin plays an important role in physiological homeostasis and disease progression. In this review, we introduce the proteins that interact with periostin, and discuss how the multi-domain structure of periostin functions as a scaffold for the assembly of interacting proteins, and how it underlies construction of highly sophisticated extracellular architectures. 相似文献