Dear all,
I thank everyone who directed me to coiled coil structures where the alpha
helical chains are related by a crystallographic axis. My question was prompted
by an examination of structures (mainly parallel homodimers) where this is not
the case. In most structures, including 2zta (the classic GCN4 leucine zipper
dimer), a strict 2 fold does not exist. In an instance such as 2zta, is the
'small' deviation from a 2-fold due to the absence of crystallographic symmetry
restraints? Also, in a structure such as tropomyosin, not only is there a
deviation from the 2-fold but the two chains themselves are not structurally
equivalent.
Best regards,
Xie
