Relative orientation of close-packed β-pleated sheets in proteins

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Abstract
When β-pleated sheets pack face to face in proteins, the angle between the strand directions of the two β-sheets is observed to be near -30°. We propose a simple model for β-sheet-to-β-sheet packing in concanavalin A, plastocyanin, γ-crystallin, superoxide dismutase, prealbumin, and the immunoglobin fragment V REI . This model shows how the observed relative orientation of two packed β-sheets is a consequence of ( i ) the rows of side chains at the interface being approximately aligned and ( ii ) the β-sheet having a right-handed twist. The special amino acid composition of residues at the β-sheet-to-β-sheet interfaces makes the contact surfaces essentially smooth and hydrophobic.