Tissues in human organ systems are strong and resilient partly due to the presense of fibulins, a family of proteins that leverage calcium binding to form strong fibers in connective tissue composites.

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One of the key factors in the evolution of multicellular organisms is the "glue" that hold cells together to form functional tissues. This connective material needs to be strong enough to withstand the constant activity required of many organ systems, yet flexible enough to bounce back from common trauma. A set of proteins, called fibulins, appear to be key components of this connective composite material, particularly because of their ability to bind calcium ions. Calcium ion bonding contributes to strong protein fibers–the reinforcement constituents of these composites.

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"The production of various forms of extracellular matrix (ECM) was an important event in early metazoan evolution—it provided the basis for the organization of multicellular tissues with a high stability that was based on cell–cell and cell–matrix interactions. The ECM is very diverse in vertebrates. It includes structures such as the large collagen fibrils that endow tendons, bones and skin with considerable mechanical strength, the thin basement membranes that maintain the differentiation of sheets of epithelial and endothelial cells, and microfibrils and elastic fibrils that provide elasticity and resilience to specialized tissues such as arteries and lungs. Many proteins have been shown to be involved in these supramolecular structures and they have been classified into several families on the basis of related domain structures and/or functions...A recent addition to the ECM proteins includes the fibulins, and five isoforms have been identified so far. They share tandem arrays of calcium-binding consensus sequences and have a diverse repertoire of interaction potentials, which makes them widespread components of the ECM." (Timpl et al. 2003:479)

"The fibulins represent a newly characterized family of calcium-binding ECM proteins and five isoforms have so far been characterized from mammalian species. The fibulins do not form large homotypic aggregates, in contrast to many other ECM proteins, but they have the ability to join other supramolecular structures as diverse as basement-membrane networks, elastic fibres, several types of microfibrils and proteoglycan aggregates. Their inclusion, in part, stabilizes these structures, but also extends their repertoire of biological functions." (Timpl et al. 2003:488)

Journal article
Fibulins: a versatile family of extracellular matrix proteinsNature Reviews Molecular Cell BiologyMay 30, 2003
Rupert Timpl, Takako Sasaki, Günter Kostka, Mon-Li Chu

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