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. 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" 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''. | ||
Biological units displayed in the 'Structure Boxes' on Proteopedia pages for PDB entries are predicted by the [[Protein Interfaces, Surfaces and Assemblies Server|PISA]] (PISA). | |||
Of course, what is 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. | Of course, what is 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. | ||
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Sometimes, the specific oligomers were not known at the time the asymmetric unit was published. Also, some authors failed to specify the biological unit even when it was known. Rarely, the specified biological units might be incorrect. For all these reasons, it is advisable to consult sources other than REMARK 350. | Sometimes, the specific oligomers were not known at the time the asymmetric unit was published. Also, some authors failed to specify the biological unit even when it was known. Rarely, the specified biological units might be incorrect. For all these reasons, it is advisable to consult sources other than REMARK 350. | ||
===Protein Interfaces, Surfaces and Assemblies Server ( | ===Protein Interfaces, Surfaces and Assemblies Server (PISA)=== | ||
The [ | The [[Protein Interfaces, Surfaces and Assemblies Server|PISA]] (PISA) at the European Bioinformatics Institute uses improved methods to predict the biological unit or probable quaternary assembly, compared to its predecessor PQS (see next section). | ||
===Probable Quaternary Structure Server (PQS)=== | ===Probable Quaternary Structure Server (PQS)=== | ||
