α/β coiled coils

• Main Authors: Marcus D Hartmann, Claudia T Mendler, Jens Bassler, Ioanna Karamichali, Oswin Ridderbusch, Andrei N Lupas, Birte Hernandez Alvarez
• Format: Article
• Language: English
• Published: eLife Sciences Publications Ltd 2016-01-01
• Series: eLife
• Subjects: α-helix; fiber; heptad repeat; sequence periodicity; supercoil
• Online Access: https://elifesciences.org/articles/11861

Coiled coils are the best-understood protein fold, as their backbone structure can uniquely be described by parametric equations. This level of understanding has allowed their manipulation in unprecedented detail. They do not seem a likely source of surprises, yet we describe here the unexpected formation of a new type of fiber by the simple insertion of two or six residues into the underlying heptad repeat of a parallel, trimeric coiled coil. These insertions strain the supercoil to the breaking point, causing the local formation of short β-strands, which move the path of the chain by 120° around the trimer axis. The result is an α/β coiled coil, which retains only one backbone hydrogen bond per repeat unit from the parent coiled coil. Our results show that a substantially novel backbone structure is possible within the allowed regions of the Ramachandran space with only minor mutations to a known fold.