What are Amino acids?

Download Amino Acid Chart as PDF:  Download

Amino Acid Table

Download Amino Acid Table as PDF:  Download

2. Non-Proteinogenic Amino Acids

Unusual or non-proteinogenic amino acids (aa) are distinct from the 22 proteinogenic amino acids that are naturally encoded in the genome for protein biosynthesis. More than 140 non-proteinogenic amino acids naturally occur in proteins. They play significant biological roles as intermediates in biosynthesis, in post-translational modification of proteins, as components of bacterial cell walls, and as neurotransmitters or toxins. 

There are different groups of natural non-proteinogenic amino acids:

Non-alpha amino acids

The amino group is located not at α carbon but second or third carbon. Examples are β-alanine and GABA (γ-aminobutyric acid).

D-amino acids

D-amino acids are of opposite chirality than the standard L-amino acids, which is the case D-alanine and D-glutamate contained in bacterial peptidoglycan.

Amino acids with no hydrogen at α carbon 

These occur in fungal aminoisobutyric acid or in dehydroamino acids whereas all proteinogenic amino acids have at least one hydrogen at the α-arbon.

Amino acids with two stereocenters

Two stereocenters will emerge when two amino acids crosslink for example if two cysteine residues form a disulfide bond to form cysteine.

Amino acid variants

Straight side chain variants occur on homoalanine, norvaline and norleucine. Variations of serine, and cysteine are homoserine, homocysteine, selenocysteine, selenohomocysteine, selenomethionine.

Post-translational modified amino acids (PTMs)

Some non-proteinogenic amino acids are nevertheless found in proteins because they are post-translationally modified variants of proteinogenic amino acids. Examples are hydroxyproline, phosphorylated aa and hypusine. 

These non-proteinogenic amino acids can be incorporated into peptides during custom peptide synthesis for all kinds of applications. In addition to the commercially available amino acids, we are able to synthesize a wide range of amino acids that are not commercially available. Please inquire about your specific requirements.

3. Unnatural Amino Acids

Besides the naturally occurring amino acids (both proteinogenic and non-proteinogenic) thousands more can be chemically synthesized. They have proven to be powerful tools in peptide synthesis, offering researchers unprecedented control over peptide structure and function. These unnatural amino acids (UAAs) are often modifications of their native analogues with a versatility of unique chemical properties, which can introduce novel functionalities and structural motifs into peptides.

Unnatural amino acids are incorporated into custom peptides for various purposes, such as increasing activity, selectivity, or plasma stability of peptides, for example to be used as inhibitors in drug discovery projects. They are also useful for investigating the structure and dynamics of proteins, to study protein interactions, or to modulate the activity of proteins in living cells. In materials science, peptides containing unnatural amino acids are used to design functional biomaterials with tailored mechanical, electrical, or optical properties. 

Unnatural amino acids can be classified into several categories based on their structural features, including non-natural side chains, modified backbone structures, and non-proteinogenic amino acids derived from natural sources or synthesized de novo. Commonly used unnatural amino acids include 

• D-amino acids
• homo amino acids
• N-methyl amino acids
• alpha-methyl amino acids
• beta (homo) amino acids
• gamma amino acids
• helix/turn stabilizing motifs
• backbone modifications (such as peptoids). 

In addition to the readily available amino acids, we can also synthesize a wide range of non-commercial amino acids for the synthesis of modified peptides. Please request a quote for your specific peptide sequence! Our peptide library service allows the incorporation of up to 200 unnatural amino acids per synthesis run, enabling the rapid generation of large combinatorial peptide libraries.

4. Chirality in Amino Acids

In proteinogenic amino acids, the α–carbon is bound to the carboxyl and amino groups as well as the R group or side chain specific to each amino acid and an hydrogen atom. With these four different groups at the α–carbon all α-amino acids are chiral except glycine (which has a second hydrogen as side chain), which means that there are two versions of a molecule that cannot by any rotation or translation be made to cover its mirror image (like our two hands). Amino acids can exist in the L and the D confirmation but all chiral proteogenic amino acids have the L configuration. However, some D-amino acids exist in nature, e.g. in bacteria, as a neuromodulator (D-serine), and in some antibiotics.

5. Amino acids in proteins

The amino acid sequence of a protein determines its three-dimensional structure and its function. Many proteins are subject to post-translational modifications, such as phosphorylation, acetylation, and glycosylation, which may change their structure and functions. Amino acids are not only the building blocks of proteins, but some are also precursors for neurotransmitters (e.g., serotonin, dopamine), signaling molecules (e.g., nitric oxide), and metabolic intermediates (e.g., α-ketoglutarate, oxaloacetate).