On the Emergence of Orientational Order in Folded Proteins with Implications for Allostery

The beautiful structures of single- and multi-domain proteins are clearly ordered in some fashion but cannot be readily classified using group theory methods that successfully used to describe periodic crystals. For this reason, protein considered aperiodic, may have evolved way for functional purposes, especially instances require a combination softness rigidity within the same molecule. By analyzing solved structures, we show orientational symmetry is broken aperiodic arrangement secondary structure elements (SSEs), which deduce by calculating nematic order parameter, P2. We find folded droplets with broad distribution argue non-zero value P2, leads an SSEs can resist external forces, requirement allosteric proteins. Such proteins, mechanical forces regions while being flexible others, transmit signals from one region another (action at distance) response binding ligands (oxygen, ATP, or other small molecules).