Dear All,
Suppose the protein crystal resolution is about 2-3A, then in the map it should
be rather difficult to distinguish the C and N in the sidechain of HIS. In this
way we may regard the sidechain of HIS is flippable. But suppose in one flipped
conformation of the HIS, the free N in the sidechain of HIS can form H-bond
with the neighbour H of the OH of the Thr, in the other flipped conformation of
the HIS, the free N in the sidechain of HIS cannot form H-bond with the
neighbour H of the OH of the Thr (caused by distance issue).
Suppose whether the H-bond forms between the free N in the sidechain of HIS and
the neighbour H of the OH of the Thr was very important biologically, in this
situation how can we distinguish whether the H-bond forms?
Smith
