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    Integral Membrane Protein

    Integral Membrane Protein

    CR1 is a large integral membrane protein which is a cellular receptor for C3b and C4b, whose function is in binding, rather than activation.

    From: Encyclopedia of Genetics, 2001

    Related terms:

    PeptideTransmembrane DomainC-TerminusN-TerminusNested GeneMutationYeastCell Membrane

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    Dancing Protein Clouds: Intrinsically Disordered Proteins in the Norm and Pathology, Part C

    Brian J. Aneskievich, ... Olga Vinogradova, in Progress in Molecular Biology and Translational Science, 2021

    5 Conclusions

    IMP disorder has been formally hypothesized15 now for over 5 years with many earlier reports of membrane protein dynamics16 open to reinterpretation in such a context. With the premise and existence of disorder within extracellular and cytoplasmic domains of TM proteins further conceptually developed,21 the scene was clearly set for new two-way evaluations of disorder and mechanisms TM proteins utilize to perform their function, including clustering, trafficking, and the inter-relationship of PTM and protein conformation. The single-pass IMPs emphasized here in the context of TM protein disorder highlight the probable impact of regional flexibility in normal physiological function of IMP as well as challenges and possible insight into pharmacological control of regional disorder to modulate IMP function in various disease states. Incorporation of disordered regions into essential cell surface receptors likely enhances formation of functional networks necessary for adaptable and efficient cross-membrane signal transduction. Nevertheless, there is much yet to be deciphered as to the consequences of intrinsic disorder for the conformation and in turn function of IMP with unstructured domains. This includes the specific assignment of presumed increased functionality to regions of disorder as well as the physiological effects of the order-disorder (and vice versa) transitions possibly occurring due to interaction with natural ligands or to pathological mutations. As highlighted in this chapter for a few TM protein examples, some separate facets of this have been done for individual proteins. It is clear that an integrative approach of bioinformatics, biophysical assessments, in vitro assembly models, and targeted mutagenesis will be the vital key for future successes in the field.

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    Analysis of Antigens Recognized by Monoclonal Antibodies

    JAMES W. GODING, in Monoclonal Antibodies (Third Edition), 1996

    Type I and Type II membrane proteins

    Integral membrane proteins may be further subdivided. Many integral membrane proteins possess a single transmembrane sequence. These may be divided into type I membrane proteins, which have a cleavable N-terminal signal sequence and a transmembrane sequence that is usually situated close to the C terminus. Type II membrane proteins have a noncleavable hydrophobic transmembrane region close to the N terminus, which serves as a combined signal/anchor sequence. Examples of type I membrane proteins include the histocompatibility antigens, glycophorin and membrane immunoglobulin. Examples of type II membrane proteins include the transferrin receptor, the asialoglycoprotein receptor, and many ecto-enzymes and glycosyl transferases.

    Many integral membrane proteins span the membrane more than once, and often many times. Either terminus may be inside or outside the cell. Proteins with multiple transmembrane domains include a large family of G-protein-coupled receptors such as rhodopsin, the coloured visual pigments, and receptors for many small molecules, as well as many pumps and channels.

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    The Folding of Proteins and Nucleic Acids

    N.D. DiBartolo, P.J. Booth, in Comprehensive Biophysics, 2012

    Abstract

    Integral membrane proteins adopt diverse structures with differing stability, flexibility, and oligomeric state. How much of this is dictated by the amino acid sequence and how much by the membrane is unknown, as are the key features that have to be mimicked in vitro to stabilize a functional membrane protein fold. Here we summarize successful approaches to fold helical membrane proteins and outline advances in kinetic studies in vitro. We also describe how studies are progressing to more complex, larger, and multisubunit proteins and put the work into context with regard to the insertion machinery involved in vivo.

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    The Erythrocyte

    John W. Harvey, in Clinical Biochemistry of Domestic Animals (Sixth Edition), 2008

    2 Integral Membrane Proteins

    Integral membrane proteins penetrate the lipid bilayer. These glycoproteins express carbohydrate residues on the outside surface of the cell. They contribute negative charge to the cell surface, function as receptors or transport proteins, and carry RBC antigens (Chasis and Mohandas, 1992; Mohandas and Chasis, 1993; Schrier, 1985). Band 3 (anion exchanger 1) is the major integral protein. It accounts for approximately one-fourth of the total membrane protein, with about 106 copies/RBC (Delaunay, 2007; Schrier, 1985). It is important as an anion transporter and provides a site for binding of the cytoskeleton internally. Additional transmembrane glycoproteins called glycophorins also help anchor and stabilize the cytoskeleton (Chasis and Mohandas, 1992).

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    Cell Membranes

    The structure and function of cells are critically dependent on membranes, which not only separate the interior of the cell from its environment but also define the internal compartments of eukaryotic cells, including the nucleus and cytoplasmic organelles. The formation of biological membranes is based on the properties of lipids, and all cell membranes share a common structural organization: bilayers of phospholipids with associated proteins. These membrane proteins are responsible for many specialized functions; some act as receptors that allow the cell to respond to external signals, some are responsible for the selective transport of molecules across the membrane, and others participate in electron transport and oxidative phosphorylation. In addition, membrane proteins control the interactions between cells of multicellular organisms. The common structural organization of membranes thus underlies a variety of biological processes and specialized membrane functions, which will be discussed in detail in later chapters.

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    The Cell: A Molecular Approach. 2nd edition.

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    Cell Membranes

    The structure and function of cells are critically dependent on membranes, which not only separate the interior of the cell from its environment but also define the internal compartments of eukaryotic cells, including the nucleus and cytoplasmic organelles. The formation of biological membranes is based on the properties of lipids, and all cell membranes share a common structural organization: bilayers of phospholipids with associated proteins. These membrane proteins are responsible for many specialized functions; some act as receptors that allow the cell to respond to external signals, some are responsible for the selective transport of molecules across the membrane, and others participate in electron transport and oxidative phosphorylation. In addition, membrane proteins control the interactions between cells of multicellular organisms. The common structural organization of membranes thus underlies a variety of biological processes and specialized membrane functions, which will be discussed in detail in later chapters.

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    Membrane Lipids

    The fundamental building blocks of all cell membranes are phospholipids, which are amphipathic molecules, consisting of two hydrophobic fatty acid chains linked to a phosphate-containing hydrophilic head group (see Figure 2.7). Because their fatty acid tails are poorly soluble in water, phospholipids spontaneously form bilayers in aqueous solutions, with the hydrophobic tails buried in the interior of the membrane and the polar head groups exposed on both sides, in contact with water (Figure 2.45). Such phospholipid bilayers form a stable barrier between two aqueous compartments and represent the basic structure of all biological membranes.

    Figure 2.45

    A phospholipid bilayer. Phospholipids spontaneously form stable bilayers, with their polar head groups exposed to water and their hydrophobic tails buried in the interior of the membrane.

    Lipids constitute approximately 50% of the mass of most cell membranes, although this proportion varies depending on the type of membrane. Plasma membranes, for example, are approximately 50% lipid and 50% protein. The inner membrane of mitochondria, on the other hand, contains an unusually high fraction (about 75%) of protein, reflecting the abundance of protein complexes involved in electron transport and oxidative phosphorylation. The lipid composition of different cell membranes also varies (Table 2.3). The plasma membrane of consists predominantly of phosphatidylethanolamine, which constitutes 80% of total lipid. Mammalian plasma membranes are more complex, containing four major phospholipids—phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, and sphingomyelin—which together constitute 50 to 60% of total membrane lipid. In addition to the phospholipids, the plasma membranes of animal cells contain glycolipids and cholesterol, which generally correspond to about 40% of the total lipid molecules.

    Table 2.3

    Lipid Composition of Cell Membranes .

    An important property of lipid bilayers is that they behave as two-dimensional fluids in which individual molecules (both lipids and proteins) are free to rotate and move in lateral directions (Figure 2.46). Such fluidity is a critical property of membranes and is determined by both temperature and lipid composition. For example, the interactions between shorter fatty acid chains are weaker than those between longer chains, so membranes containing shorter fatty acid chains are less rigid and remain fluid at lower temperatures. Lipids containing unsaturated fatty acids similarly increase membrane fluidity because the presence of double bonds introduces kinks in the fatty acid chains, making them more difficult to pack together.

    Figure 2.46

    Mobility of phospholipids in a membrane. Individual phospholipids can rotate and move laterally within a bilayer.

    Because of its hydrocarbon ring structure (see Figure 2.9), cholesterol plays a distinct role in determining membrane fluidity. Cholesterol molecules insert into the bilayer with their polar hydroxyl groups close to the hydrophilic head groups of the phospholipids (Figure 2.47). The rigid hydrocarbon rings of cholesterol therefore interact with the regions of the fatty acid chains that are adjacent to the phospholipid head groups. This interaction decreases the mobility of the outer portions of the fatty acid chains, making this part of the membrane more rigid. On the other hand, insertion of cholesterol interferes with interactions between fatty acid chains, thereby maintaining membrane fluidity at lower temperatures.

    Figure 2.47

    Insertion of cholesterol in a membrane. Cholesterol inserts into the membrane with its polar hydroxyl group close to the polar head groups of the phospholipids.

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    Membrane Proteins

    Proteins are the other major constituent of cell membranes, constituting 25 to 75% of the mass of the various membranes of the cell. The current model of membrane structure, proposed by Jonathan Singer and Garth Nicolson in 1972, views membranes as a fluid mosaic in which proteins are inserted into a lipid bilayer (Figure 2.48). While phospholipids provide the basic structural organization of membranes, membrane proteins carry out the specific functions of the different membranes of the cell. These proteins are divided into two general classes, based on the nature of their association with the membrane. Integral membrane proteins are embedded directly within the lipid bilayer. Peripheral membrane proteins are not inserted into the lipid bilayer but are associated with the membrane indirectly, generally by interactions with integral membrane proteins.

    Source : www.ncbi.nlm.nih.gov

    Chapter 12 Flashcards

    Study with Quizlet and memorize flashcards terms like (EOC Q12) In a hydrophobic environment, a homopolymer of _____ would most likely form a(n) _____., In phosphoglycerides, fatty acids are esterified at, In the movement of small molecules across a lipid bilayer, the permeability coefficient can be correlated with and more.

    Chapter 12

    (EOC Q12) In a hydrophobic environment, a homopolymer of _____ would most likely form a(n) _____.

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    alanine; α-helix

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    In phosphoglycerides, fatty acids are esterified at

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    glycerol carbons 1 and 2.

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    1/19 Created by Colton_Marshall4

    Terms in this set (19)

    (EOC Q12) In a hydrophobic environment, a homopolymer of _____ would most likely form a(n) _____.

    alanine; α-helix

    In phosphoglycerides, fatty acids are esterified at

    glycerol carbons 1 and 2.

    In the movement of small molecules across a lipid bilayer, the permeability coefficient can be correlated with

    the solubility of the molecule in a nonpolar solvent.

    (EOC Q2) What structure would most likely form if phospholipids were placed in an organic solvent?

    an "inside out" membrane with head groups away from the solvent

    (EOC Q11) What functional group is found in platelet-activating factor that makes it unique in comparison with other phospholipids?

    ether

    (EOC Q6 and 7) Oleic acid has 18 carbons and one double bond, while palmitoleic acid has 16 carbons and one double bond. How would you expect the melting point of trans-oleic acid to compare with that of cis-palmitoleic acid?

    Both the increased length and presence of a trans double bond in trans-oleic acid would significantly increase the melting point relative to cis-palmitoleic acid.

    The most common way in which integral membrane proteins span the membrane is in

    α-helical segments.

    Although salts of fatty acids form micelles, phospholipids and glycolipids form bimolecular sheets because of

    the presence of two fatty acyl chains.

    Lipid molecules are said to be amphipathic, meaning that

    they have a dual nature with part of the molecule being hydrophobic and the other part hydrophilic.

    Of the three major types of membrane lipids, which is NOT found in prokaryotes?

    cholesterol

    (EOC Q15) Each intracellular fusion of a vesicle with a membrane requires a SNARE protein on the vesicle (called the v-SNARE) and a SNARE protein on the target membrane (called the t-SNARE). Assume that a genome encodes 11 members of the v-SNARE family and 7 members of the t-SNARE family. With the assumption of no specificity, how many potential v-SNARE-t-SNARE interactions could take place?

    77

    (EOC Q14) A culture of bacteria growing at 37°C was shifted to 25°C. Which of the following best explains the alteration of fatty acid composition of the membrane phospholipids?

    shorter chains with more cis double bonds

    Unsaturated fatty acids have double bonds that are in the cis, rather than the trans, configuration. One of the consequences of this is

    a bend in the molecule.

    (EOC Q10) Which of the following lipids is least likely to flip-flop across a membrane?

    gangliosides

    The main use of hydropathy plots is to

    identify membrane-spanning helical regions in integral membrane proteins.

    (EOC Q19) Which of the following agents, commonly used in the isolation of membrane proteins, often presents problems in later purification or crystallization steps?

    detergents

    (EOC Q8) Which of the following best explains the difference in the membranes of a hibernating animal when compared with a nonhibernating animal?

    more polyunsaturated fatty acids in the hibernating animal

    Which of the following would be expected to lower the Tm for a phospholipid bilayer?

    replacing a lipid containing 18-C fatty acids with one containing 16-C fatty acids.

    Which of the following is NOT a difference of archaeal membrane lipids relative to those of other organisms?

    A backbone other than glycerol is used.

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