In coiled-coil (CC) protein structures α-helices wrap around one another to form rope-like assemblies. Most natural and designed CCs have two-four helices and cyclic (C n ) or dihedral (D n ) symmetry. Increasingly, CCs with five or more helices are being reported ...
In coiled-coil (CC) protein structures α-helices wrap around one another to form rope-like assemblies. Most natural and designed CCs have two-four helices and cyclic (C n ) or dihedral (D n ) symmetry. Increasingly, CCs with five or more helices are being reported. A subset of these higher-order CCs is of interest as they have accessible central channels that can be functionalised; they are α-helical barrels. These extended cavities are surprising given the drive to maximise buried hydrophobic surfaces during protein folding and assembly in water. Here, we show that α-helical barrels can be maintained by the strategic placement of β-branched aliphatic residues lining the lumen. Otherwise, the structures collapse or adjust to give more-complex multi-helix assemblies without C n or D n symmetry. Nonetheless, the structural hallmark of CCs-namely, knobs-into-holes packing of side chains between helices-is maintained leading to classes of CCs hitherto unobserved in nature or accessed by design.
Organizational Affiliation:
School of Biochemistry, University of Bristol, Medical Sciences Building, University Walk, Bristol, BS8 1TD, UK. D.N.Woolfson@bristol.ac.uk.
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