An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the pathogen, called an antigen. Each tip of the "Y" of an antibody contains a paratope that is specific for one particular epitope on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize it directly.
CD32, also known as FcγRII or FCGR2, is a surface receptor glycoprotein belonging to the Ig gene superfamily. CD32 can be found on the surface of a variety of immune cells. CD32 has a low-affinity for the Fc region of IgG antibodies in monomeric form, but high affinity for IgG immune complexes. CD32 has two major functions: cellular response regulation, and the uptake of immune complexes. Cellular responses regulated by CD32 include phagocytosis, cytokine stimulation, and endocytic transport. Dysregulated CD32 is associated with different forms of autoimmunity, including systemic lupus erythematosus. In humans, there are three major CD32 subtypes: CD32A, CD32B, and CD32C. While CD32A and CD32C are involved in activating cellular responses, CD32B is inhibitory.
Immunoglobulin M (IgM) is the largest of several isotypes of antibodies that are produced by vertebrates. IgM is the first antibody to appear in the response to initial exposure to an antigen; causing it to also be called an acute phase antibody. In humans and other mammals that have been studied, plasmablasts in the spleen are the main source of specific IgM production.
Protein tags are peptide sequences genetically grafted onto a recombinant protein. Tags are attached to proteins for various purposes. They can be added to either end of the target protein, so they are either C-terminus or N-terminus specific or are both C-terminus and N-terminus specific. Some tags are also inserted at sites within the protein of interest; they are known as internal tags.
The immunoglobulin heavy chain (IgH) is the large polypeptide subunit of an antibody (immunoglobulin). In human genome, the IgH gene loci are on chromosome 14.
In immunology, an Fc receptor is a protein found on the surface of certain cells – including, among others, B lymphocytes, follicular dendritic cells, natural killer cells, macrophages, neutrophils, eosinophils, basophils, human platelets, and mast cells – that contribute to the protective functions of the immune system. Its name is derived from its binding specificity for a part of an antibody known as the Fc region. Fc receptors bind to antibodies that are attached to infected cells or invading pathogens. Their activity stimulates phagocytic or cytotoxic cells to destroy microbes, or infected cells by antibody-mediated phagocytosis or antibody-dependent cell-mediated cytotoxicity. Some viruses such as flaviviruses use Fc receptors to help them infect cells, by a mechanism known as antibody-dependent enhancement of infection.
Protein A is a 42 kDa surface protein originally found in the cell wall of the bacteria Staphylococcus aureus. It is encoded by the spa gene and its regulation is controlled by DNA topology, cellular osmolarity, and a two-component system called ArlS-ArlR. It has found use in biochemical research because of its ability to bind immunoglobulins. It is composed of five homologous Ig-binding domains that fold into a three-helix bundle. Each domain is able to bind proteins from many mammalian species, most notably IgGs. It binds the heavy chain within the Fc region of most immunoglobulins and also within the Fab region in the case of the human VH3 family. Through these interactions in serum, where IgG molecules are bound in the wrong orientation, the bacteria disrupts opsonization and phagocytosis.
Protein G is an immunoglobulin-binding protein expressed in group C and G streptococcal bacteria much like protein A but with differing binding specificities. It is a ~60-kDA cell surface protein that has found application in purifying antibodies through its binding to the Fab and Fc region. The native molecule also binds albumin, but because serum albumin is a major contaminant of antibody sources, the albumin binding site has been removed from recombinant forms of protein G. This recombinant protein G, either labeled with a fluorophore or a single-stranded DNA strand, was used as a replacement for secondary antibodies in immunofluorescence and super-resolution imaging.
The immunoglobulin light chain is the small polypeptide subunit of an antibody (immunoglobulin).
In immunology, antibodies are classified into several types called isotypes or classes. The variable (V) regions near the tip of the antibody can differ from molecule to molecule in countless ways, allowing it to specifically target an antigen . In contrast, the constant (C) regions only occur in a few variants, which define the antibody's class. Antibodies of different classes activate distinct effector mechanisms in response to an antigen . They appear at different stages of an immune response, differ in structural features, and in their location around the body.
Protein A/G is a recombinant fusion protein that combines IgG binding domains of both protein A and protein G. Protein A/G contains four Fc binding domains from protein A and two from protein G, yielding a final mass of 50,460 daltons. The binding of protein A/G is less pH-dependent than protein A, but otherwise has the additive properties of protein A and G.
Nuclear transcription factor Y subunit beta is a protein that in humans is encoded by the NFYB gene.
Immunoglobulin kappa constant, also known as IGKC, is a human gene that encodes the constant domain of kappa-type light chains for antibodies. It is found on chromosome 2, in humans, within the Immunoglobulin kappa locus, IGK@.
Ig gamma-1 chain C region is a protein that in humans is encoded by the IGHG1 gene.
Immunoglobulin heavy constant alpha 1 is a immunoglobulin gene with symbol IGHA1. It encodes a constant (C) segment of Immunoglobulin A heavy chain. Immunoglobulin A is an antibody that plays a critical role in immune function in the mucous membranes. IgA shows the same typical structure of other antibody classes, with two heavy chains and two light chains, and four distinct domains: one variable region, and three variable regions. As a major class of immunoglobulin in body secretions, IgA plays a role in defending against infection, as well as preventing the access of foreign antigens to the immunologic system.
The basic structure of immunoglobulin (Ig) molecules is a tetramer of two light chains and two heavy chains linked by disulphide bonds. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). There are five types of heavy chains: alpha, delta, epsilon, gamma and mu, all consisting of a variable domain (VH) and three or four constant domains. Ig molecules are highly modular proteins, in which the variable and constant domains have clear, conserved sequence patterns. The domains in Ig and Ig-like molecules are grouped into four types: V-set, C1-set, C2-set and I-set. Structural studies have shown that these domains share a common core Greek-key beta-sandwich structure, with the types differing in the number of strands in the beta-sheets as well as in their sequence patterns.
Affitins are artificial proteins with the ability to selectively bind antigens. They are structurally derived from the DNA binding protein Sac7d, found in Sulfolobus acidocaldarius, a microorganism belonging to the archaeal domain. By randomizing the amino acids on the binding surface of Sac7d and subjecting the resulting protein library to rounds of ribosome display, the affinity can be directed towards various targets, such as peptides, proteins, viruses, and bacteria.
In molecular biology, the protein domain b1 refers to the domain b1 of Protein L. L is a bacterial protein with immunoglobulin (Ig) light chain-binding properties. It contains a number of homologous b1 repeats towards the N terminus. These repeats have been found to be responsible for the interaction of protein L with Ig light chains. N-terminus domain contains five homologous B1 repeats of 72-76 amino acids each.
Protein M is an immunoglobulin-binding protein originally found on the cell surface of the human pathogenic bacterium Mycoplasma genitalium. It is presumably a universal antibody-binding protein, as it is known to be reactive against all antibody types tested so far. It is capable of preventing the antigen-antibody interaction due to its high binding affinity to any antibody. The Scripps Research Institute announced its discovery in 2014. It was detected from the bacterium while investigating its role in patients with a cancer, multiple myeloma.
Anti-immunoglobulin antibodies are defined as a protein that detects other antibodies from an organism. Specifically, anti-immunoglobulin antibodies are created by B-cells as antibodies to bind to other immunoglobulins. Immunoglobulins have two regions: the constant region and the variable region. The constant region is involved in effector function, while the variable region is involved in recognizing and binding to antigens. Anti-immunoglobulin antibodies may bind to either the variable or constant region of the immunoglobulin. Anti-immunoglobulin antibodies are a type of secondary antibody. They are able to detect primary antibodies through multiple methods such as a Western blot, immunohistochemistry, immunofluorescence staining, flow cytometry, and ELISA.
