Terminology and Usage
As with many biological terms, the use of protein family is somewhat context dependent; it may indicate large groups of proteins with the lowest possible level of detectable sequence similarity, or very narrow groups of proteins with almost identical sequence, function, and three-dimensional structure, or any kind of group in-between. To distinguish between these situations, Dayhoff introduced the concept of a protein superfamily. Other terms such as protein class, protein group, and protein sub-family have been coined over the years, but all suffer similar ambiguities of usage. A common usage is that superfamilies contain families which contain sub-families. It is unlikely that an exact definition will be agreed and to it is up to the reader to discern exactly how these terms are being used in a particular context.
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