Not sure what you mean by "constrained", but it you mean more rigid, then you are right.
All proteinogenic (
Except for Proline, the R-chain (" Residu "-chain) is only connected to the "backbone" via the
The structure for Proline is slightly different, in that the Aminogroup is part of the sidechain ( R):
This imposes some structural constraints on the peptide:
Due to it's sharp angle formed in the peptide bond between the Proline N -atom and the Carboxyl-group of the next AA, Proline is usually found at breaks in the secondary structure of the chain.
It is often found at the start and end of