Side-Chains Configurations in Coiled Coils Revealed by the 5.15-Å Meridional Reflection on Hard α-Keratin X-Ray Diffraction Patterns
Résumé
The origin of the 5.15-Å meridional reflection on hard-keratin X-ray diffraction patterns is discussed in terms of side-chains conformations. We show it to reveal specific configurations of the side chains which are common to all two-stranded-heli-cal coiled coils. Combining literature data on cryst-allised coiled coil pieces and molecular dynamics results with our X-ray diffraction pattern simulations , we propose rules for the attribution of 1 torsion angles for coiled coils involved in fibres whose structure cannot be resolved at atomic resolution: in a (a b c d e f g) heptad repeat, a and d residues, respectively, adopt mean t and g configurations , whereas statistical rules are given for the other residues. 1999 Academic Press