The L27 domain is a

protein domain In molecular biology, a protein domain is a region of a protein's polypeptide chain that is self-stabilizing and that folds independently from the rest. Each domain forms a compact folded three-dimensional structure. Many proteins consist of s ...

that is found in receptor targeting proteins Lin-2 and Lin-7 (

LIN7A Lin-7 homolog A is a protein that in humans is encoded by the ''LIN7A'' gene. Interactions LIN7A has been shown to interact with: * CASK, * DLG1, and * KCNJ12 ATP-sensitive inward rectifier potassium channel 12 is a lipid-gated ion channel t ...

LIN7B Lin-7 homolog B is a protein that in humans is encoded by the ''LIN7B'' gene. Interactions LIN7B has been shown to interact with: * ACCN3, * GRIN2B, * KCNJ12 ATP-sensitive inward rectifier potassium channel 12 is a lipid-gated ion channel t ...

LIN7C Lin-7 homolog C is a protein that in humans is encoded by the ''LIN7C'' gene. Interactions LIN7C has been shown to interact with: * DLG1, * KCNJ12 ATP-sensitive inward rectifier potassium channel 12 is a lipid-gated ion channel that in human ...

), as well as some

protein kinase A protein kinase is a kinase which selectively modifies other proteins by covalently adding phosphates to them (phosphorylation) as opposed to kinases which modify lipids, carbohydrates, or other molecules. Phosphorylation usually results in a fu ...

s and human

MPP2 MAGUK p55 subfamily member 2 is a protein that in humans is encoded by the ''MPP2'' gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' ...

protein. The L27 domain is a

protein interaction Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

module that exists in a large family of scaffold proteins, functioning as an organisation centre of large protein assemblies required for the establishment and maintenance of

cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

polarity. L27 domains form specific

heterotetrameric A tetrameric protein is a protein with a quaternary structure of four subunits (tetrameric). Homotetramers have four identical subunits (such as glutathione S-transferase), and heterotetramers are complexes of different subunits. A tetramer ...

complexes, in which each domain contains three

alpha-helices The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues ear ...

. The L27_2 domain is a protein-protein interaction domain capable of organising

scaffold protein In biology, scaffold proteins are crucial regulators of many key signalling pathways. Although scaffolds are not strictly defined in function, they are known to interact and/or bind with multiple members of a signalling pathway, tethering them in ...

s into supramolecular assemblies by formation of

heteromeric A heteromer is something that consists of different parts; the antonym of homomeric. Examples are: Biology * Spinal neurons that pass over to the opposite side of the spinal cord. * A protein complex that contains two or more different polypeptide ...

L27_2 domain complexes. L27_2 domain-mediated

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

assemblies have been shown to play essential roles in

cellular Cellular may refer to: *Cellular automaton, a model in discrete mathematics * Cell biology, the evaluation of cells work and more * ''Cellular'' (film), a 2004 movie *Cellular frequencies, assigned to networks operating in cellular RF bands *Cell ...

processes including asymmetric

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

, establishment and maintenance of

cell polarity Cell polarity refers to spatial differences in shape, structure, and function within a cell. Almost all cell types exhibit some form of polarity, which enables them to carry out specialized functions. Classical examples of polarized cells are desc ...

, and clustering of

receptor Receptor may refer to: * Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...

s and

ion channels Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...

. Members of this family form specific heterotetrameric complexes, in which each domain contains three

. The two

N-terminal The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the ami ...

helices A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helices, ...

of each L27_2 domain pack together to form a tight, four-helix bundle in the

heterodimer In biochemistry, a protein dimer is a macromolecular complex formed by two protein monomers, or single proteins, which are usually non-covalently bound. Many macromolecules, such as proteins or nucleic acids, form dimers. The word ''dimer'' has ...

, whilst the third

helix A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helices, ...

of each L27_2 domain forms another four-helix bundle that assembles the two units of the

into a

tetramer A tetramer () (''tetra-'', "four" + '' -mer'', "parts") is an oligomer formed from four monomers or subunits. The associated property is called ''tetramery''. An example from inorganic chemistry is titanium methoxide with the empirical formula Ti ...

. The L27_N domain is often found at the N-terminus of the L27 domain. It plays a role in the

biogenesis Spontaneous generation is a superseded scientific theory that held that living creatures could arise from nonliving matter and that such processes were commonplace and regular. It was hypothesized that certain forms, such as fleas, could arise fr ...

tight junction Tight junctions, also known as occluding junctions or ''zonulae occludentes'' (singular, ''zonula occludens''), are multiprotein junctional complexes whose canonical function is to prevent leakage of solutes and water and seals between the epith ...

s and in the establishment of cell polarity in

epithelial cell Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

s. Each L27_N domain consists of three alpha-helices, the first two of which form an antiparallel

coiled-coil A coiled coil is a structural motif in proteins in which 2–7 alpha helix, alpha-helices are coiled together like the strands of a rope. (Protein dimer, Dimers and Protein trimer, trimers are the most common types.) Many coiled coil-type protei ...

. Two L27 domains come together to form a four-helical bundle with the antiparallel coiled-coils formed by the first two

. The third

of each domain forms another coiled-coil packing at one end of the four-helix bundle, creating a large

hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, th ...

interface: the

interactions are the major force that drives

formation.

References

Further reading