In addition to the specific amino acid codes, placeholders are used in cases where chemical or crystallographic analysis of a peptide or protein cannot conclusively determine the identity of a residue.
Ambiguous Amino Acids
3-Letter
1-Letter
Asparagine or aspartic acid
Asx
B
Glutamine or glutamic acid
Glx
Z
Leucine or Isoleucine
Xle
J
Unspecified or unknown amino acid
Xaa
X
Unk is sometimes used instead of Xaa, but is less standard.
In addition, many non-standard amino acids have a specific code. For example, several peptide drugs, such as Bortezomib and MG132, are artificially synthesized and retain their protecting groups, which have specific codes. Bortezomib is Pyz-Phe-boroLeu, and MG132 is Z-Leu-Leu-Leu-al. To aid in the analysis of protein structure, photocrosslinking amino acid analogues are available. These include photoleucine (pLeu) and photomethionine (pMet).[97]
A The codon AUG both codes for methionine and serves as an initiation site: the first AUG in an mRNA‘s coding region is where translation into protein begins.[30]
Amino Acid and Codon Table
Table of standard amino acid abbreviations and properties
neutral(90%)
In addition, there are two additional amino acids that are incorporated by overriding stop codons:
In addition to the specific amino acid codes, placeholders are used in cases where chemical or crystallographic analysis of a peptide or protein cannot conclusively determine the identity of a residue.
Unk is sometimes used instead of Xaa, but is less standard.
In addition, many non-standard amino acids have a specific code. For example, several peptide drugs, such as Bortezomib and MG132, are artificially synthesized and retain their protecting groups, which have specific codes. Bortezomib is Pyz-Phe-boroLeu, and MG132 is Z-Leu-Leu-Leu-al. To aid in the analysis of protein structure, photocrosslinking amino acid analogues are available. These include photoleucine (pLeu) and photomethionine (pMet).[97]
RNA codon table
more