Laminin
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Laminin is a protein found in the extracellular matrix, the sheets of protein that form the substrate of all internal organs also called the basement membrane. It is the major non-collagenous component of the basal lamina, such as those on which cells of an epithelium sit.[1] It has four arms that can bind to four other molecules. The three shorter arms are particularly good at binding to other laminin molecules, which is what makes it so great at forming sheets. The long arm is capable of binding to cells, which helps anchor the actual organs to the membrane.
Structurally, the laminin protein is made up of three polypeptide chains - α, β and γ, giving it a total of six "ends", accounting for a lot of its flexibility in connecting various molecules. Its pliable nature gives it a mixed appearance in the body, but stretched out, as mostly depicted in diagrams, it resembles a cross.[2]
They are a family of glycoproteins that are an integral part of the structural scaffolding in almost every animal tissue. Laminins are secreted and incorporated into cell-associated extracellular matrices.
Laminin is vital to making sure overall body structures hold together. Improper production of laminin can cause muscles to form improperly, leading to a form of muscular dystrophy.
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[edit] Types
Each laminin molecule is a heterotrimer assembled from alpha-, beta-, and gamma-chains.[3]
Fifteen laminin trimers have been identified.
[edit] Networks
Laminins form independent networks and are associated with type IV collagen networks via entactin, and perlecan. They also bind to cell membranes through integrin receptors and other plasma membrane molecules, such as the dystroglycan glycoprotein complex and Lutheran blood group glycoprotein.[1] Through these interactions, laminins critically contribute to cell attachment and differentiation, cell shape and movement, maintenance of tissue phenotype, and promotion of tissue survival.[1][3] Some of these biological functions of laminin have been associated with specific amino-acid sequences or fragments of laminin.[1] For example, the peptide sequence [GTFALRGDNGDNGQ], which is located on the alpha-chain of laminin, promotes adhesion of endothelial cells.[4]
[edit] Pathology
Dysfunctional structure of one particular laminin, laminin-2, is the cause of one form of congenital muscular dystrophy[5]. Laminin-2 is composed of an α2, a β1 and a γ1 chains. This laminin's distribution includes the brain and muscle fibers. In muscle, it binds to alpha dystroglycan and integrin alpha7 – beta1 via the G domain, and via the other end binds to the extracellular matrix.
[edit] Role in Neural Development
Laminin-1 is a major substrate along which nerve axons will grow, both in vivo and in vitro. For example, it lays down a path that developing retinal ganglion cells follow on their way from the retina to the tectum. It is also often used as a substrate in cell culture experiments. Interestingly, the presence of laminin-1 can influence how the growth cone responds to other cues. For example, growth cones are repelled by netrin when grown on laminin-1, but are attracted to netrin when grown on fibronectin. This effect of laminin-1 probably occurs through a lowering of intracellular cyclic AMP.
[edit] References
- ^ a b c d M. A. Haralson and John R. Hassell (1995). Extracellular matrix: a practical approach. Ithaca, N.Y: IRL Press. ISBN 0-19-963220-0.
- ^ page 149 Beck K, Hunter I, Engel J (February 1990). "Structure and function of laminin: anatomy of a multidomain glycoprotein". FASEB J. 4 (2): 148–60. PMID 2404817.
- ^ a b Colognato H, Yurchenco P (2000). "Form and function: the laminin family of heterotrimers". Dev. Dyn. 218 (2): 213–34. doi:. PMID 10842354.
- ^ Beck et al., 1999.
- ^ Hall, TE et al. (2007). Proc Natl Acad Sci USA 104 (17), 7092-7097 doi: 10.1073/pnas.0700942104
[edit] External links
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