Biological Unit: Difference between revisions
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The "Biological Unit" is the quaternary structure of a protein that is believed to be the functional form of the molecule. It can be a single chain, or a quaternary assembly of multiple identical or non-identical chains. For example, the biological unit of hemoglobin includes two alpha chains and two beta chains, making it a tetrameric α<sub>2</sub>β<sub>2</sub> structure. | ==Definition== | ||
The "Biological Unit" is the quaternary structure of a protein that is believed to be the functional form of the molecule. It can be a single chain, or a quaternary assembly of multiple identical or non-identical chains. For example, the biological unit of hemoglobin includes two alpha chains and two beta chains, making it a tetrameric α<sub>2</sub>β<sub>2</sub> structure. When a biological unit contains multiple chains that have co-evolved to bind to each other, it may also be referred to as a ''specific oligomer''. | |||
Of course, what is the biological unit under one set of conditions may change under a different set of conditions, so there may be more than one biological unit that includes a given protein chain. | Of course, what is the biological unit under one set of conditions may change under a different set of conditions, so there may be more than one biological unit that includes a given protein chain. | ||
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Published macromolecular structure data files ([[Atomic coordinate files]], often in the [[PDB file format]]) contain the [[Asymmetric Unit]], which may be identical with the biological unit, or only a portion of it, or may contain multiple biological units. When publishing a macromolecular structure, the authors may elect to specify the biological unit. In the [[PDB file format]], this is done in REMARK 350. | Published macromolecular structure data files ([[Atomic coordinate files]], often in the [[PDB file format]]) contain the [[Asymmetric Unit]], which may be identical with the biological unit, or only a portion of it, or may contain multiple biological units. When publishing a macromolecular structure, the authors may elect to specify the biological unit. In the [[PDB file format]], this is done in REMARK 350. | ||
Atomic coordinates for biological units, when specified by the authors of a published structure, are available from the [[Protein Data Bank]]. When this was written (April, 2008), biological units were available at the bottom of the list under the ''Download Files'' section, under the ''Structure'' tab (upper left of the page). | ==Sources of Biological Unit Models== | ||
===REMARK 350 in the PDB File Header=== | |||
Atomic coordinates for biological units, when specified by the authors of a published structure, are available from the [[Protein Data Bank]]. When this was written (April, 2008), biological units were available at the bottom of the list under the ''Download Files'' section, under the ''Structure'' tab (upper left of the page). One technical problem with these files is that when they contain more than one copy of the asymmetric unit, the chains all have identical names. | |||
===Probable Quaternary Structure=== | |||
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