Biological Sciences
Receptors
Receptors are specialized proteins located on the surface of cells or within cells that can recognize and bind to specific molecules, such as hormones, neurotransmitters, or drugs. When a molecule binds to a receptor, it triggers a specific cellular response, such as a change in the cell's activity or gene expression. Receptors play a crucial role in cell signaling and communication within the body.
Written by Perlego with AI-assistance
Related key terms
1 of 5
6 Key excerpts on "Receptors"
eBook - PDF- Paul Leff(Author)
- 1998(Publication Date)
- CRC Press(Publisher)
(4,5). With this explosion of new information about receptor structure and even their distribution it becomes essential to reconsider the way we approach the characterization and classification of Receptors for neurotransmitters, hormones, and auta-7 8 Humphrey coids. Only two receptor superfamilies will be exemplified here, the hepta-helical G-protein-linked Receptors and the multimeric ligand-gated ion channel Receptors, which in mediating the wide variety of effects of numer-ous neurotransmitters have been the most studied by pharmacologists to date. The two other major structural classes of receptor are the enzyme-linked Receptors (e.g., for insulin and growth factors) and the nuclear recep-tors (e.g., for steroids). Even today, the precise definition of a receptor is problematic. Certainly Stephenson's long-established definition of that spatial arrangement of atoms to which a substance endogenous to the organism attaches itself as an essential step in modifying cellular function no longer seems appropriate (6). Nevertheless it can be argued that it is still essential to classify Receptors according to their natural ligands, because of the critical importance of such information in understanding the functional role of a given receptor or recep-tors in the whole body. In the light of modern knowledge, a receptor must now be regarded as a macromolecule, which may or may not be a single molecular entity, with multiple sites of interaction (7-9). The individual proteins can be defined in terms of their corresponding genes, but there may be local mo-lecular differences according to the host cell, in terms of variable patterns of glycosylation and different transcriptional splice variants (10-14). A modern definition of a receptor has been suggested as the entire protein molecule or cluster of molecules which can selectively recognize and be collectively activated by an endogenous ligand (agonist) to mediate a cellular event (15).
eBook - PDF- Mannfred A. Hollinger(Author)
- 2007(Publication Date)
- CRC Press(Publisher)
Regardless of how rigid one’s denition of receptor is, receptor theory provides a unifying concept for the explanation of the effect of endogenous or xenobiotic chemicals on biological systems. Although the great preponderance of drugs interact with membrane Receptors or some intracellular sites, there are, however, a few exceptions. Examples of nonreceptor-mediated drug action include Drug Receptors 75 antacids such as sodium bicarbonate, which act to buffer excess hydrogen ions; chelating agents such as ethylenediaminetetraacetic acid, which form inactive complexes with inorganic ions; and osmotic cathar- tics such as magnesium sulfate, which produce their pharmacological response by attracting water. NATURE OF Receptors Proteins, glycoproteins, proteolipids, and associated proteinaceous species appear to be particularly suited to act as Receptors because they can assume three-dimensional congurations. The three- dimensional shape is the net result of primary, secondary, and tertiary structures. Three-dimensionality requires that drugs, or any binding ligand, achieve binding specicity, referred to as “induced t.” If the drug is an active one, the result of this binding is believed to be a conformational change in the receptor, with subsequent modication of membrane permeability or activation of intracellular enzymes “downstream.” The concept of a “lock and key” relationship between drug and receptor is based on the analo- gous hypothesis of the German chemist and enzymologist Emil Fischer who originally developed the theory in relation to the interaction between enzymes and substrates. In 1895, Fischer wrote that an enzyme’s specic effect might be explained, “by assuming that the intimate contact between the molecules necessary for the release of the chemical reaction is possible only with similar geometrical congurations.
- Kenneth H. Lundstrom, Mark L. Chiu(Authors)
- 2005(Publication Date)
- CRC Press(Publisher)
Their functions are extremely diverse as they regulate many physiological processes related to neurological and neurodegenerative functions, cardiovascular mechanisms, and metabolic control. 1 GPCRs can also act as co-Receptors for cellular entry of the human immune de fi ciency virus (HIV). 2 Extracellular signaling is triggered through hormones, neurotransmitters, chemokines, calcium ions, light, and odorants and leads to the activation of GPCRs, resulting in a cascade of signaling through various cellular pathways. 3 The GPCR designation relates to the intracellular signaling through guanine nucleotide-binding proteins (G proteins) although alternative mechanisms have been described recently. 4 The estimated number of GPCRs in the human genome is 800. A large number belong to the subfamily of odorant Receptors. Due to their many essential physio-logical functions, GPCRs play an important role in drug discovery. More than 60% of the current drug targets are focused on GPCRs and a quarter of the 200 top selling drugs are based on GPCRs. 5 The various indications and the more detailed mecha-nisms of drug and GPCR interactions are described in subsequent chapters. Common to all GPCRs is their topology of seven transmembrane-spanning domains (7TMs) consisting of a -helical structures and they are therefore also called 7TM Receptors. Each GPCR possesses an extracellular N-terminus and an intracellular C-terminus with various intracellular and extracellular loop regions connecting the transmembrane regions. This chapter will describe the different families of GPCRs, their functions, and their couplings to G proteins. Alternative signaling mechanisms for GPCRs are also discussed. Finally, the cellular traf fi cking of GPCRs is described. 2.2 FAMILIES OF GPCRs The overall amino acid sequence homology among GPCRs is rather low. Certain homologous regions arise from sequence alignment of the 7TMs within the GPCR families.
eBook - PDF- M.G. Ord, L.A. Stocken(Authors)
- 1997(Publication Date)
- Elsevier Science(Publisher)
Chapter 6 TALKING TO CELLS-CELL MEMBRANE Receptors AND THEIR MODES OF ACTION Robin F. Irvine Introduction 173 Membrane Receptors 175 Coupling of Receptors to Intracellular Signals 182 Acknowledgments 196 References 196 INTRODUCTION This chapter is essentially about the field of research that we now know as signal transduction or cellular signaling. Currently this field comprises a significant proportion of the world's total research in the life sciences. This is not surprising if one thinks about it. The cells of our tissues are under the constant control of hormones, neurotransmitters, and growth factors, which are telling the cells to do this, do that, stop doing this, do that instead, etc. The great majority of these outside influences—agonists is a useful all-embracing term—are water-soluble. They have to be because they move and work in an aqueous environment. So, when they come up against the hydrophobic cell membrane (plasma membrane) of any cell, they must either be taken up into the cell by an active process (e.g. endocytosis, active transport) which is necessarily slow, or they must bind to a specific recognition site (a receptor) in the plasma membrane, which then registers their presence by sending a chemical signal into the cell. Signal transduction, therefore, is all 173 174 ROBIN F. IRVINE about the nature of these chemical messages, how they are generated after the receptor has bound its ligand (the agonist), and how the cell uses them to alter its function. Because these receptor-generated signals plug-into and modulate the homeostatic control mechanisms of a cell's functions, it is inevitable that in understanding receptor-mediated signal transduction we will understand the fundamentals of cellular function.
- A. Kleinzeller(Author)
- 2012(Publication Date)
- Elsevier Science(Publisher)
II. Receptor-mediated transmembrane signalling Although the principal function of the cell membrane is to maintain an effective barrier between the extracellular and intracellular milieu, there are highly specialized membrane-localized constituents {e.g. ion channels, nutrient transporters MEMBRANE Receptors 195 and pharmacologic Receptors) that can be singled out as play-ing particularly pivotal roles in terms of selectively transmit-ting information from the external to the internal cellular en-vironment (and in some cases, vice versa). The pharmacologic Receptors situated in the plasma membrane possess not only the ability to recognize extracellular hormonal signalling mol-ecules with high affinity and specificity, but also the capacity, once combined with the specific ligand, to transmit informa-tion across the cell membrane, so as activate intracellular sig-nalling pathways. The possibility of transmitting information from surface Receptors to intracellular sites was visualized early on by Peters (1937) who was impressed by Clark's obser-vations (1937). It is this dual recognition-transmembrane sig-nalling property, by which the receptor per se acts as a mes-sage generating system, that distinguishes Receptors from other cell surface recognition/transport constituents. The sec-tions below will, with selected examples, focus on the general mechanisms whereby cell surface Receptors generate a trans-membrane signal. Receptors for agonists that act via intracel-lular Receptors (e.g. steroid hormones) will not be discussed. 1. GENERAL MECHANISMS OF TRANSMEMBRANE SIGNALLING AND THE MOBILE RECEPTOR PARADIGM To fulfil their recognition/action function, membrane recep-tors must be able to generate an intracellular signal that can be greatly amplified.
eBook - PDF- Bernard L. Horecker, Earl R. Stadtman(Authors)
- 2014(Publication Date)
- Academic Press(Publisher)
Hormone Receptors as Regulators of Hormone Action I RALPH A. BRADSHAW I WILLIAM A. FRAZIER I Departments of Biological I Chemistry and Neurobiology I Division of Biology and Biomedical I Sciences I Washington University I St. Louis, Missouri I. Introduction II. The Elements of the Hormonal Response A. Hormone Structure B. Receptors C. Intracellular Response III. Regulation of the Hormonal Response .. A. Regulation of Receptor Affinity B. Regulation of Receptor Number IV. Mechanism of the Hormonal Response .. A. Cell Surface Receptors B. Intracellular Receptors V. Summary References I. Introduction As multicellular organisms evolved and became more complex, the necessity arose for rapid and specific intercellular communication so that cells and tissues could respond in an appropriately coordinate manner to changing internal and environmental conditions. Two methods have evolved for this purpose. One means by which the or-ganism provides for coordinated metabolic activity is the nervous sys-tem, which allows for extremely rapid communication among cells in even distant parts of the largest multicellular organisms. The other means of coordinated regulation, which probably evolved before chemi-cal neurotransmission as we know it today, is the diffusion of chemical messengers between distant cells. The multiplicity of hormones and the diversity of metabolic processes which they regulate underscore the importance which hormonal regulatory systems have assumed in the maintenance of homeostasis in complex organisms. This chapter will deal primarily with the interaction of so-called target cells with polypeptide hormone-like substances as a representa-tive class of recognitive interactions between a cell and regulatory l l 2 2 6 12 14 15 25 29 29 31 34 35 2 RALPH A. BRADSHAW AND WILLIAM A. FRAZIER messengers.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
