To qualify as fulcrum for hinge-motion, residue must bear very little tertiary structure packing constraints on its main chain. The hinge lies outside the interface between the two domains inter-connected by the hinge. On hinge-opening the motion is perpendicular to the plane of the interface, which is lost after opening. The closed conformation is usually stabilised by a bound ligand. This is necessarily so, for if the closed conformation is strongly held together without a ligand, then the hinge opening will have to cross a high energy barrier.
Shear motions occur parallel to the interface between closely packed segments of polypeptides.
This type of motion is more severely constrained with additional packing contacts due to interdigitating side chains. A large enough sheared domain motion is due to the combination of a number of shear movements. Hinged-motion occurs in the context of secondary structure interactions. Hinge motion at extended strand involves a few large changes in main chain torsion angles at the hinge connecting two domains, constrained only by the Ramachandran allowance of torsional angles. In beta-sheets two adjacent strands can move like hinges of a door, with extra constraint of hydrogen bonds that hold the sheet together.