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Macromolecules consisting of long sequences of α-amino acid s [H2N–CHR–COOH] in peptide (amide) linkage (elimination of H2O between the α-NH2 and α-COOH of successive residues). P. is three-fourths of the dry weight of most cell matter and is involved in structures, hormones, enzymes, muscle contraction, immunologic response, and essential life functions. The amino acid s involved are generally the 20 α-amino acid s (glycine, l-alanine, etc.) recognized by the genetic code. Cross-links yielding globular forms of p. are often effected through the –SH groups of two l-cysteinyl residues, as well as by noncovalent forces (hydrogen bonds, lipophilic attractions, etc.). [G. protos, first, + -in]
- p. 4.1 a peripheral p. that binds tightly to spectrin in the red cell membrane; it also binds to certain glycophorins and helps determine the shape and flexibility of the red blood cell.
- p. A a component of some strains of Staphyloccocus aureus.
- acute phase p. plasma proteins associated with inflammation including C-reactive p. (CRP), mannose-binding p., serum amyloid P component, α1-antitrypsin, fibrinogen, ceruloplasmin, and complement components C9 and factor B, the concentrations of which increase in response to interleukins 1, 6, and 11.
- acyl carrier p. (ACP) one of the proteins of the complex in cytoplasm that contains all of the enzymes required to convert acetyl-CoA (and, in certain cases, butyryl-CoA or propionyl-CoA) and malonyl-CoA to palmitic acid. This complex is tightly bound together in mammalian tissues and in yeast, but that from Escherichia coli is readily dissociated. The ACP thus isolated is a heat-stable p. with a molecular weight of about 10,000. It contains a free –SH that binds the acyl intermediates in the synthesis of fatty acid s as thioesters. This –SH group is part of a 4′-phosphopantetheine, added to the apoprotein by ACP phosphodiesterase, which thus plays the same role that it does in coenzyme A. ACP is involved in every step of the fatty acid synthetic process.
- androgen binding p. (ABP) a p. secreted by testicular Sertoli cells along with inhibin and müllerian inhibiting substance. Androgen binding p. probably maintains a high concentration of androgen in the seminiferous tubules.
- antitermination p. a p. that permits RNA polymerase to transcribe through certain termination sites.
- antiviral p. (AVP) a human or animal factor, induced by interferon in virus-infected cells, which mediates interferon inhibition of virus replication.
- autologous p. any p. found normally in the fluids or tissues of the body.
- Bence Jones proteins proteins with unusual thermosolubility found in the urine of patients with multiple myeloma, consisting of monoclonal immunoglobulin light chains. See Bence Jones reaction. SEE ALSO: immunoglobulin. [H. Bence Jones, English physician, 1813–1873]
- p. C a vitamin K–dependent glycoprotein that inhibits coagulation by enzymatic cleavage of the activated forms of factors V and VIII, and thus interferes with the regulation of intravascular clot formation; a deficiency of p. C leads to impaired regulation of blood coagulation. There is an autosomal dominant deficiency [MIM*176860] that, like antithrombin III deficiency and plasminogen deficiency, is associated with an increased risk of severe or premature thrombosis.
- capping proteins proteins that bind to one end of actin filaments, preventing both addition and loss of actin monomers.
- catabolite (gene) activator p. (CAP) a p. that can be activated by cAMP, whereupon it affects the action of RNA polymerase by binding it with it or near it on the DNA to be transcribed. SYN: cAMP receptor p., catabolite gene activator.
- cholesterol ester transport proteins a p. that transports cholesterol esters from HDL to VLDL and LDL; a deficiency of this p. is associated with elevated HDL cholesterol.
- circumsporozoite p. one of two proteins (the other is thrombospondin-related adhesive p.) involved in sporozoite recognition of host cells in malaria.
- cis-acting p. a p. that acts on the molecule of DNA from which it was expressed.
- compound p. SYN: conjugated p..
- conjugated p. p. attached to some other molecule or molecules (not amino acid in nature) otherwise than as a salt; e.g., flavoproteins; chromoproteins, hemoglobins. SEE ALSO: prosthetic group. Cf.:simple p.. SYN: compound p..
- corticosteroid-binding p. SYN: transcortin.
- C-reactive p. (CRP) a β-globulin found in the serum of various persons with certain inflammatory, degenerative, and neoplastic diseases; although the p. is not a specific antibody, it precipitates in vitro the C polysaccharide present in all types of pneumococci.
- denatured p. a p. whose characteristics or properties have been altered in some way, as by heat, enzyme action, or chemicals, and in so doing has lost its biologic activity.
- docking p. in the process of translating proteins that are to be secreted from the cell, translation is arrested until the growing polypeptide chain that is complexed by a specific particle (signal recognition particle) comes in contact with this integral p. of the endoplasmic reticulum.
- eosinophil cationic p. (ECP) p. the level of which in serum of clotted blood reflects the rate of activation of circulating eosinophils.
- extrinsic proteins SYN: peripheral proteins.
- fatty acid –binding p. SYN: Z-p..
- fibrous p. any insoluble p., including the collagens, elastins, and keratins, involved in structural or fibrous tissues.
- foreign p. a p. that differs from any p. normally found in the organism in question. SYN: heterologous p..
- G proteins intracellular membrane-associated proteins activated by several ( e.g., β-adrenergic) receptors; they serve as second messengers or transducers of the receptor-initiated response to intracellular elements such as enzymes to initiate an effect. These proteins have a high affinity for guanine nucleotides and hence are named G proteins. SYN: G-p., GTP binding proteins.
- G-p. SYN: G proteins.
- glial fibrillary acidic p. a cytoskeletal p. of 51 kd found in fibrous astrocytes; stains for this p. are frequently used to assist in the differential diagnosis of neurologic lesions.
- globular p. any p. soluble in water, usually with added acid, alkali, salt, or ethanol, and roughly so classified (albumins, globulins, histones, and protamines), in contrast to fibrous p..
- GTP binding proteins SYN: G proteins.
- heat shock proteins (hsp) specific proteins whose synthesis is increased immediately after sudden elevation of temperature; their function is to help diminish the harmful effects of high temperature.
- heterologous p. SYN: foreign p..
- integral proteins proteins that cannot be easily separated from a biomembrane. SYN: intrinsic proteins.
- iron-sulfur proteins proteins containing one or more iron atoms that are linked to sulfur bridges and/or sulfur of cysteinyl residues; e.g., certain proteins in the electron transport pathway.
- p. kinase C any of a number of cytoplasmic calcium-activated kinases involved in numerous processes, including hormonal binding, platelet activation, and tumor promotion.
- p. kinases a class of enzymes that phosphorylates other proteins; many of these kinases are responsive to other effectors ( e.g., cAMP, cGMP, insulin, epidermal growth factor, calcium and calmodulin, calcium and phospholipids).
- M p. 1. SYN: Streptococcus M antigen. SEE ALSO: β-hemolytic streptococci, under streptococcus, Streptococcus pneumoniae. 2. SYN: monoclonal immunoglobulin.
- macrophage inflammatory p. (MIP) (mak′ro-faj in′flam-ma-to-re) a member of the chemokine family that is chemotactic for certain lymphocyte subsets such as T cytotoxic cells.
- mannose-binding p. a p. involved in innate immunity that can bind mannosylated microorganisms and activate the complement pathway.
- microtubule-associated proteins (MAPs) proteins that have a specific association with α- and/or β-tubulin; e.g., tau, MAP1, MAP2; several have been found in the plaques observed in Alzheimer disease.
- monoclonal p. SYN: monoclonal immunoglobulin.
- monocyte chemoattractant p.-1 (MCP-1) secreted by endothelial cells of a blood vessel wall; it induces extravasation of monocytes.
- myelin p. A1 SYN: encephalithogenic p..
- native p. the concept of a p. in its natural state, in the cell, unaltered by heat, chemicals, enzyme action, or the exigencies of extraction.
- neutrophil-activating p. old term for interleukin-8.
- nonspecific p. a p. substance that elicits a response not mediated by specific antigen-antibody reaction.
- odorant binding p. proteins in nasal mucus that bind lipophilic odor-producing molecules and transfer them to the olfactory receptors. Similar proteins may mediate taste.
- p. p53 a multifunctional p. that modulates gene transcription and controls DNA repair, apoptosis, and the cell cycle.
- parathyroid hormone-related p. a 140–amino acid p. secreted by some cancer cells; it causes hypercalcemia. SYN: parathyroid hormonelike p..
- pathologic proteins paraprotein.
- peripheral proteins pathways that can be easily removed from a biomembrane ( E.G., by altering the pH or the ionic strength). SYN: extrinsic proteins.
- phenylthiocarbamoyl p. formed by the reaction of phenylisothiocyanate with a terminal α-amino group of a peptide or p. SEE ALSO: phenylisothiocyanate, phenylthiohydantoin. SYN: PhNCS p., PTC p..
- PhNCS p. SYN: phenylthiocarbamoyl p..
- p. phosphatases a class of enzymes that catalyze the dephosphorylation of specific phosphorylated proteins.
- plasma proteins dissolved proteins (>100) of blood plasma, mainly albumins and globulins (normally 6–8 g/100 mL); they hold fluid in blood vessel s by osmosis and include antibodies and blood-clotting proteins. SYN: serum proteins.
- protective p. SYN: antibody.
- PTC p. SYN: phenylthiocarbamoyl p..
- receptor p. an intracellular p. (or p. fraction) that has a high specific affinity for binding a known stimulus to cellular activity, such as a steroid hormone or adenosine 3′,5′-cyclic phosphate.
- S p. the major fragment produced from pancreatic ribonuclease by the limited action of subtilisin, which cleaves the ribonuclease between residues 20 and 21; the smaller fragment (residues 1–20) is S peptide.
- simple p. p. that yields only α-amino acid s or their derivatives by hydrolysis; e.g., albumins, globulins, glutelins, prolamines, albuminoids, histones, protamines. Cf.:conjugated p..
- stimulatory p. 1 (SP1) an RNA polymerase II transcription factor in vertebrates; binds to DNA in regions rich in G and C residues; a general promoter-binding factor necessary for the activation of many genes.
- structure proteins proteins whose role is for structure and support in tissue and within the cell; E.G., the collagens.
- surfactant-specific proteins the p. components of pulmonary surfactant, including surfactant p. A, B, C.
- thrombospondin-related adhesive p. one of two proteins (the other is circumsporozoite p.) involved in sporozoite recognition of host cells in malaria.
- thyroxine-binding p. (TBP) 1. SYN: thyroxine-binding globulin. 2. SYN: thyroxine-binding prealbumin.
- unwinding proteins enzymes that uncoil the DNA allowing recombination events to occur.
- whey p. the soluble p. contained in the whey of milk clotted by rennin; e.g., lactoglobulin, α-lactalbumin, lactoferrin.
- Z-p. a fatty acid –binding p. that participates in the intracellular movement of fatty acid s. SYN: fatty acid –binding p..
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pro·tein 'prō-.tēn, 'prōt-ē-ən n, often attrib
1) any of numerous naturally occurring extremely complex substances (as an enzyme or antibody) that consist of amino acid residues joined by peptide bonds, contain the elements carbon, hydrogen, nitrogen, oxygen, usu. sulfur, and occas. other elements (as phosphorus or iron), that are essential constituents of all living cells, that are synthesized from raw materials by plants but assimilated as separate amino acids by animals, that are both acidic and basic and usu. colloidal in nature although many have been crystallized, and that are hydrolyzable by acids, alkalies, proteolytic enzymes, and putrefactive bacteria to polypeptides, to simpler peptides, and ultimately to alpha-amino acids
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n.
one of a group of organic compounds of carbon, hydrogen, oxygen, and nitrogen (sulphur and phosphorus may also be present). The protein molecule is a complex structure made up of one or more chains of amino acid, which are linked by peptide bonds. Proteins are essential constituents of the body; they form the structural material of muscles, tissues, organs, etc., and are equally important as regulators of function, as enzymes and hormones. Proteins are synthesized in the body from their constituent amino acids, which are obtained from the digestion of protein in the diet. Excess protein, not required by the body, can be converted into glucose and used as an energy source.
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pro·tein (proґtēn) [Gr. prōtos first] any of a group of complex organic compounds which contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur, the characteristic element being nitrogen. Proteins, the principal constituents of the protoplasm of all cells, are of high molecular weight and consist essentially of combinations of α-amino acids in peptide linkages. Twenty different amino acids are commonly found in proteins, and each protein has a unique genetically defined amino acid sequence which determines its specific shape and function. Their roles include enzymatic catalysis, transport and storage, coordinated motion, nerve impulse generation and transmission, control of growth and differentiation, immunity, and mechanical support. proteinic adjMedical dictionary. 2011.