The human cyclophilin family, as represented by the structures of the isomerase domains of some of its members
A protein family is a group of evolutionarily related proteins. In many cases, a protein family has a corresponding gene family, in which each gene encodes a corresponding protein with a 1:1 relationship. The term "protein family" should not be confused with family as it is used in taxonomy.
Proteins in a family descend from a common ancestor and typically have similar three-dimensional structures, functions, and significant sequence similarity.[1][2] Sequence similarity (usually amino-acid sequence) is one of the most common indicators of homology, or common evolutionary ancestry.[3][4] Some frameworks for evaluating the significance of similarity between sequences use sequence alignment methods. Proteins that do not share a common ancestor are unlikely to show statistically significant sequence similarity, making sequence alignment a powerful tool for identifying the members of protein families.[3][4] Families are sometimes grouped together into larger clades called superfamilies based on structural similarity, even if there is no identifiable sequence homology.
Currently, over 60,000 protein families have been defined,[5] although ambiguity in the definition of "protein family" leads different researchers to highly varying numbers.
^"What are protein families? Protein classification". EMBL-EBI. Retrieved 2023-11-14.
^Orengo, Christine; Bateman, Alex (2013). "Introduction". In Orengo, Christine; Bateman, Alex (eds.). Protein Families: Relating Protein Sequence, Structure, and Function. Hoboken, New Jersey: John Wiley & Sons, Inc. pp. vii–xi. doi:10.1002/9781118743089.fmatter. ISBN 9781118743089.
^ abPearson, William R. (2013). "An Introduction to Sequence Similarity ("Homology") Searching". Current Protocols in Bioinformatics. 3: 3.1.1–3.1.8. doi:10.1002/0471250953.bi0301s42. ISSN 1934-3396. PMC 3820096. PMID 23749753.
^ abChen, Junjie; Guo, Mingyue; Wang, Xiaolong; Liu, Bin (2018-03-01). "A comprehensive review and comparison of different computational methods for protein remote homology detection". Briefings in Bioinformatics. 19 (2): 231–244. doi:10.1093/bib/bbw108. ISSN 1477-4054. PMID 27881430.
^Kunin, Victor; Cases, Ildefonso; Enright, Anton J.; de Lorenzo, Victor; Ouzounis, Christos A. (2003). "Myriads of protein families, and still counting". Genome Biology. 4 (2): 401. doi:10.1186/gb-2003-4-2-401. ISSN 1474-760X. PMC 151299. PMID 12620116.
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a family of related proteins that are expressed in all animal cell lineages and organs. All Ras proteinfamily members belong to a class of protein called...
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