Protein domain
<p>Feb 05, 2017 05:58 PM essential!</p>
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A <b >protein domain</b> is a conserved part of a given protein sequence and <a href="https://en.wikipedia.org/wiki/Tertiary_structure" class="mw-redirect" title="Tertiary structure" >(tertiary) structure</a> that can <a href="https://en.wikipedia.org/wiki/Biological_evolution" class="mw-redirect" title="Biological evolution" >evolve</a>, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and <a href="https://en.wikipedia.org/wiki/Protein_folding" title="Protein folding" >folded</a>. Many proteins consist of several structural domains. One domain may appear in a variety of different proteins. <a href="https://en.wikipedia.org/wiki/Molecular_evolution" title="Molecular evolution" >Molecular evolution</a> uses domains as building blocks and these may be recombined in different arrangements to create <a href="https://en.wikipedia.org/wiki/Protein" title="Protein" >proteins</a> with different functions. Domains vary in length from between about 25 amino acids up to 500 amino acids in length<sup class="noprint Inline-Template Template-Fact" >[<i><a href="https://en.wikipedia.org/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed" >citation needed</a></i>]</sup>. The shortest domains such as <a href="https://en.wikipedia.org/wiki/Zinc_fingers" class="mw-redirect" title="Zinc fingers" >zinc fingers</a> are stabilized by metal ions or <a href="https://en.wikipedia.org/wiki/Disulfide_bond" class="mw-redirect" title="Disulfide bond" >disulfide bridges</a>. Domains often form functional units, such as the calcium-binding <a href="https://en.wikipedia.org/wiki/EF-hand" class="mw-redirect" title="EF-hand" >EF hand domain</a> of <a href="https://en.wikipedia.org/wiki/Calmodulin" title="Calmodulin" >calmodulin</a>. Because they are independently stable, domains can be "swapped" by <a href="https://en.wikipedia.org/wiki/Genetic_engineering" title="Genetic engineering" >genetic engineering</a> between one protein and another to make <a href="https://en.wikipedia.org/wiki/Chimera_(protein)" class="mw-redirect" title="Chimera (protein)" >chimeric proteins</a>.</p>
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