Biological Unit: Difference between revisions
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The ''Biological Unit'', also called the ''Biological Assembly''<ref name="xudunbrackpreprint" /><ref name="xudunbrack" />, is the quaternary structure of a protein that is believed to be the main 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''. | The ''Biological Unit'', also called the ''Biological Assembly''<ref name="xudunbrackpreprint" /><ref name="xudunbrack" />, is the quaternary structure of a protein that is believed to be the main 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, | Of course, the functional form (biological unit) under one set of conditions may change under a different set of conditions, so there may be more than one functional form (biological unit) that includes a given protein chain. For example, phosphorylation or dephosphorylation by protein kinases or phosphatases often change the affinities between proteins, and hence their quaternary assemblies. | ||
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. Interchain contacts that occur in the asymmetric unit that are absent in the biological unit are termed [[crystal contacts]]. 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. Interchain contacts that occur in the asymmetric unit that are absent in the biological unit are termed [[crystal contacts]]. 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. | ||