Due to the fact that glycine has a hydrogen
in place of the beta-carbon
, the alpha-carbon of the backbone
is less sterically constrained and has more freedom of bend and rotation. If you plot backbone dihedral angles on phi-psi Ramachandran plot
, glycine can occupy parts of phase space that are inaccessible to the other 19 natural amino acids
As a result, glycine is often found in protein loops - sections of the protein that bridge secondary structure elements. Becuase of the backbone flexibility, then make good turns between rigid units. They are also found preferentially in 'hinge' regions of a protein where a protein undergoes a conformational change. A conserved glycine in a class of proteins is indicative of conserved need for flexibility.