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--- glossary:greek_key [2008/08/07 12:46] – cuff
+++ glossary:greek_key [2008/09/18 13:50] (current) – garner
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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}}

CATH