Proline (abbreviated as Pro or P) is an α- amino acid, one of the twenty main amino acids. Its codons are CCU, CCC, CCA, and CCG.It isn't essential, meaning the human body can make it. Uniquely among the 23 protein-forming amino acids, its amine nitrogen is bound to not one but two alkyl groups, thus making it a secondary amine (proline is sometimes called an imino acid).The more common.roline is one of the two amino acids that do not follow along with the typical Ramachandran plot, along with glycine. Due to the ring formation connected to the beta carbon, the ψ and φ angles about the peptide bond have fewer allowable degrees of rotation.