The tyrosine corner: a feature of most Greek key beta-barrel proteins.
The Tyr corner is a conformation in which a tyrosine (residue "Y") near the beginning or end of an antiparallel beta-strand makes an H bond from its side-chain OH group to the backbone NH and/or CO of residue Y - 3, Y - 4, or Y - 5 in the nearby connection. The most common "classic" case is a delta 4 Tyr corner (more than 40 examples listed), in which the H bond is to residue Y - 4 and the Tyr chi 1 is near -60 degrees. Y - 2 is almost always a glycine, whose left-handed beta or very extended beta conformation helps the backbone curve around the Tyr ring. Residue Y - 3 is in polyproline II conformation (often Pro), and residue Y - 5 is usually a hydrophobic (often Leu) that packs next to the Tyr ring. The consensus sequence, then, is LxPGxY, where the first x (the H-bonding position) is hydrophilic. Residues Y and Y - 2 both form narrow pairs of beta-sheet H-bonds with the neighboring strand. delta 5 Tyr corners have a 1-residue insertion between the Gly and Tyr, forming a beta-bulge. One protein family has a delta 4 corner formed by a His rather than a Tyr, and several examples use Trp in place of Tyr. For almost all these cases, the protein or domain is a Greek key beta-barrel structure, the Tyr corner ends a Greek key connection, and it is well-conserved in related proteins. Most low-twist Greek key beta-barrels have 1 Tyr corner. "Reverse" delta 4 Tyr corners (H bonded to Y + 4) and other variants are described, all less common and less conserved. It seems likely that the more classic Tyr corners (delta 4, delta 5, and delta 3 Tyr, Trp, or His) contribute to the stability of a Greek key connection over a hairpin connection, and also that they may aid in the process of folding up Greek key structures.
Hemmingsen
J M
JM
Department of Biochemistry, Duke University, Durham, North Carolina 27710.
Gernert
K M
KM
Richardson
J S
JS
Richardson
D C
DC
D000595:Amino Acid Sequence; D001400:Azurin / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry; D003459:Crystallins / Q000737:chemistry; D005353:Fibronectins / Q000737:chemistry; D006860:Hydrogen Bonding; D007136:Immunoglobulins / Q000737:chemistry; D008969:Molecular Sequence Data; D011228:Prealbumin / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013482:Superoxide Dismutase / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry*; D009353:Zinostatin / Q000737:chemistry
D001426:Bacterial Proteins; D003459:Crystallins; D005353:Fibronectins; D007136:Immunoglobulins; D011228:Prealbumin; C017079:mauC protein, Methylobacterium extorquens; D001400:Azurin; D014443:Tyrosine; D009353:Zinostatin; D013482:Superoxide Dismutase