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| + | {{tag>beta}} | ||
| + | ====== Greek Key ======= | ||
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| + | This is a four-stranded [[glossary:beta_sheet | beta sheet ]] [[glossary:motif | motif]] which is characterised by +3, -1, -1 | ||
| + | connectivities in a two-dimensional schematic diagram of a protein structure, as shown here. The diagram on the left shows an N-type Greek key motif, whilst on the right is a C-type Greek key. | ||
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| + | {{:glossary:greek_keyn.gif?400|}}{{:glossary:greek_keyc.gif?400|}} | ||
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| + | In three dimensions, the motif adopts a variety of structures. | ||
| + | The Greek key can be considered as a chain folded in half, then twisted | ||
| + | around to form a pattern like that commonly seen on Greek vases. | ||
| + | Greek keys can occur with all four participating strands in the same beta sheet, or in two different sheets. A four-stranded Greek key motif can be defined by the following rules: | ||
| + | four sequential strands must be either in one, or at most, in two different beta sheets; | ||
| + | within any one sheet the participating strands must be hydrogen bonded together; hydrogen-bonded strands within one sheet must be antiparallel; and strands 1 and 4 must be hydrogen bonded. | ||
| + | |||
| + | The example structure shown here is the beta/gamma crystallin domain (CATH domain ID 1prrA01). | ||
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| + | {{cath:feature>1prrA01}} | ||
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| + | ===== References ===== | ||
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| + | {{pubmed>long:7020376}} | ||
| + | {{pubmed>long:8506258}} | ||
