An intein is a segment of a protein that is able to excise itself and rejoin the remaining portions (the exteins) with a peptide bond. Inteins have also been called "protein introns". A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O). ... Diagram of the location of introns and exons within a gene. ...

Most reported inteins also contain an endonuclease domain that plays a role in intein propagation. In fact, many genes have unrelated intein-coding segments inserted at different positions. For these and other reasons, inteins (or more properly, the gene segments coding for inteins) are sometimes called selfish genetic elements but it may be more accurate to call them parasitic. Endonucleases are enzymes that cleave the phosphodiester bond within a nucleotide chain. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... A parasite is an organism that spends a significant portion of its life in or on the living tissue of a host organism and which causes harm to the host without immediately killing it. ...

Intein-mediated protein splicing occurs after mRNA has been translated into a protein. This precursor protein contains three segements - an N-extein followed by the intein followed by a C-extein. After splicing has taken place, the result is also called an extein. Protein splicing is an intramolecular reaction of a particular protein in which an internal protein segment (called an intein) is removed from a precursor protein with a ligation of C-terminal and N-terminal external proteins (called exteins) on both sides. ... The interaction of mRNA in a eukaryote cell. ...

The first intein was discovered in 1987. Since then, inteins have been found in all three domains of life (eukaryotes, bacteria, and archaea). The mechanism for the splicing effect is nature's analogy to the technique for chemically generating medium-sized proteins called native chemical ligation, which was developed at the same time as inteins were discovered. 1987 (MCMLXXXVII) was a common year starting on Thursday of the Gregorian calendar. ... Native chemical ligation is a technique for constructing a large peptide from two smaller peptides, a C-terminal thioester peptide and a N-terminal cysteine peptide. ...

Inteins in biotechnology

Inteins are very efficient at protein splicing and they have accordingly found an important role in biotechnology. There are more than 200 inteins identified to date, sizes range from 100-800 aa. Inteins have been engineered for particular applications such as protein synthesis, and the selective labeling of protein segments, which is useful for NMR studies of large proteins. Biotechnology is a technology based on biology, especially when used in agriculture, food science, and medicine. ... Pacific Northwest National Laboratorys high magnetic field (800 MHz) NMR spectrometer being loaded with a sample. ...

Pharmaceutical inhibition of intein excision may be useful tool for drug development, the protein that contains the intein will not carry out its normal function if the intein does not excise since its structure will be disrupted. It has been suggested that this article or section be merged into Pharmacology. ...

Intein naming conventions

The first part of an intein name is based on the scientific name of the organism in which it is found, and the second part is based on the name of the corresponding gene or extein. For example, the intein found in Thermoplasma acidophilum and associated with 'Vacuolar ATPase subunit A' (VMA) is called 'Tac VMA'. In biology, binomial nomenclature is the formal method of naming species. ... In biology and ecology, an organism (in Greek organon = instrument) is a complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. ...

Normally, as in this example, just three letters suffice to specify the organism, but there are variations. For example, additional letters may be added to indicate a strain. If more than one intein is encoded in the corresponding gene, the inteins are given a numerical suffix starting from 5' to 3' or in order of their identification. For example, "Msm dnaB-1".

The segment of the gene that encodes the intein is usually given the same name as the intein, but to avoid confusion, the name of the intein proper is usually capitalized (e.g. Pfu RIR1-1), whereas the name of the corresponding gene segment is italicized.

Full and mini inteins

Inteins can contain a homing endonuclease gene domain in addition to the splicing domains. This domain is responsible for the spread of the intein by cleaving DNA at an intein free allele on the homologous chromosome, triggering the DNA double-stranded break repair system, which then repairs the break, thus copying the intein into a previously intein free site. The HEG domain is not necessary for intein splicing, and so it can be lost, forming a minimal, or mini intein. Several studies have demonstrated the modular nature of inteins by adding or removing HEG domains and determining the activity of the new construct. Two chromosomes are said to be homologous when they have the same alleles at the same positions (loci) for all the genes they contain, besides being of the same length. ...

Split inteins

Sometimes, the intein of the pre-cursor protein comes from two genes. In this case, the intein is said to be a split intein. For example, in Cyanobacteria, DnaE, the catalytic subunit alpha of DNA polymerase III, is encoded by two separate genes, dnaE-n and dnaE-c. The dnaE-n product consists of an N-extein sequence followed by a 123-aa (amino acid) intein sequence, whereas the dnaE-c product consists of a 36-aa intein sequence followed by a C-extein sequence. Orders The taxonomy of the Cyanobacteria is currently under revision. ...

External links

• The Intein Database
• Shmuel Pietrokovski's Intein database