Knobs-into-holes bonding

Knobs-into-holes bonding 71,334 in coiled coil 71... 

Each coat subunit in the Ff viruses is coiled into an a-helical rod of 7 nm length. These are arranged in the virus in a right-handed helical pattern with a pitch of 1.5 nm and with 4.4 subunits per turn (Fig. 7-7). The protein rods are inclined to the helix axis and extend inward. This arrangement permits a "knobs-in-holes" hydrophobic bonding between subunits. The helix of pitch 1.5 nm is the primary or one-start helix. However, in every regular helical structure we can also trace a two-start helix, a three-start helix, etc. In this instance the five-start helix is easiest to see. 

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