effector protein

In biology, an effector is a general term that can refer to several types of molecules or cells. In the context of biological system regulation, an effector is an element of a regulation loop controlling a regulated quantity. Small molecule effectors * A

small molecule In molecular biology and pharmacology, a small molecule or micromolecule is a low molecular weight (≤ 1000 daltons) organic compound that may regulate a biological process, with a size on the order of 1 nm. Many drugs are small molecules; ...

that selectively binds to a protein to regulate its

biological activity In pharmacology, biological activity or pharmacological activity describes the beneficial or adverse effects of a drug on living matter. When a drug is a complex chemical mixture, this activity is exerted by the substance's active ingredient or ...

can be called an effector. In this manner, effector molecules act as

ligands In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ...

that can increase or decrease

enzyme activity Enzyme assays are laboratory methods for measuring enzyme, enzymatic activity. They are vital for the study of enzyme kinetics and enzyme inhibitor, enzyme inhibition. Enzyme units The quantity or concentration of an enzyme can be expressed in Mo ...

gene expression Gene expression is the process (including its Regulation of gene expression, regulation) by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, proteins or non-coding RNA, ...

, influence

cell signaling In biology, cell signaling (cell signalling in British English) is the Biological process, process by which a Cell (biology), cell interacts with itself, other cells, and the environment. Cell signaling is a fundamental property of all Cell (biol ...

, or other protein functions. An example of such an effector is oxygen, which is an

allosteric In the fields of biochemistry and pharmacology an allosteric regulator (or allosteric modulator) is a substance that binds to a site on an enzyme or receptor distinct from the active site, resulting in a conformational change that alters the p ...

effector of

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

- oxygen binding to one of the four hemoglobin subunits greatly increases the affinity of the rest of the subunits to oxygen. Certain drug molecules also fall into this category - for example the antibiotic

rifampicin Rifampicin, also known as rifampin, is an ansamycin antibiotic used to treat several types of bacterial infections, including tuberculosis (TB), ''Mycobacterium avium'' complex, leprosy, and Legionnaires' disease. It is almost always used tog ...

used in the treatment of tuberculosis binds the initiation σ factor subunit of the bacterial RNA polymerase, preventing the transcription of bacterial genes. * The term can also be used to describe small molecules that can directly bind to and regulate the expression of

mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein. mRNA is ...

s. One example for such an effector is guanine, which can be recognised by specific sequences (known as

riboswitch In molecular biology, a riboswitch is a regulatory segment of a messenger RNA molecule that binds a small molecule, resulting in a change in Translation (biology), production of the proteins encoded by the mRNA. Thus, an mRNA that contains a ribo ...

es) found on mRNAs, and its binding to those sequences prevents the

translation Translation is the communication of the semantics, meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The English la ...

of the mRNA into a protein. See also: purine riboswitch. Protein effectors * An effector can also be used to refer to a protein that is involved in cellular signal transduction cascades. Such an example are RAS effector proteins, which are all able to bind RAS.GTP, but trigger different cell pathways upon doing so - such as the Ras-Raf-MEK-ERK pathway, the PI3K pathway or several others. * An effector hormone is a hormone that acts on a particular tissue - an example of such a hormone is

thyroxine Thyroxine, also known as T4, is a hormone produced by the thyroid gland. It is the primary form of thyroid hormone found in the blood and acts as a prohormone of the more active thyroid hormone, triiodothyronine (T3). Thyroxine and its acti ...

(T4), which regulates metabolism in many tissues throughout the body. * Antibody Effectors are effectors involved with the production and secretion of molecules involved in pathogen defense, such as Immunoglobulin. Many antibodies then act as effector molecules for the immune system of the organism. * Bacterial effector proteins are proteins injected by (usually

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

ic) bacterial cells into the cells of their host. The injected proteins serve different functions dependent on the bacteria of origin, but typically serve the purpose of inhibiting the host cells immune response. An example of these are the Transcription activator-like effector (TALE) proteins secreted by bacteria from the genus ''Xanthomonas''. * Fungal effectors are secreted by pathogenic or beneficial fungi into and around host cells by invasive hyphae to disable defense components or facilitate colonization. Protein secretion systems in fungi involve the

Spitzenkörper The Spitzenkörper (German language, German for 'pointed body', SPK) is a structure found in fungal hyphae that is the organizing center for hyphal growth and morphogenesis. It consists of many small vesicle (biology), vesicles and is present in ...

. RNA effectors * Certain plant pathogens, such as ''Botrytis cinerea,'' secrete

small RNA Small RNA (sRNA) are polymeric RNA molecules that are less than 200 nucleotides in length, and are usually non-coding RNA, non-coding. RNA silencing is often a function of these molecules, with the most common and well-studied example being RNA int ...

s (sRNAs) into the host cells and downregulate plant proteins involved in the immune response by

RNA interference RNA interference (RNAi) is a biological process in which RNA molecules are involved in sequence-specific suppression of gene expression by double-stranded RNA, through translational or transcriptional repression. Historically, RNAi was known by ...

. Effector cells * In immunology, effector cells are cells of either the

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