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glossary:greek_key [2008/09/17 11:46]
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glossary:greek_key [2008/09/18 13:50] (current)
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 +
 +{{tag>beta}}
 +====== Greek Key =======
 +
 +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.
 +
 +{{:glossary:greek_keyn.gif?400|}}{{:glossary:greek_keyc.gif?400|}}
 +
 +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). 
 +
 +{{cath:feature>1prrA01}}
 +
 +===== References =====
 +
 +{{pubmed>long:7020376}}
 +{{pubmed>long:8506258}}
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