Last night I went to a “first Friday” open-house at The Odin in north Austin and met some people working on some very interesting projects. I met one of the co-founders of trilobio, a startup company working on “revolutionizing synthetic biology by changing the way synthetic biologists do science”.
Yesterday, I wrote about Alanine, the first common amino acid assigned a letter by IUPAC for bioinformatics research. The letter B is not assigned to a single amino acid but is instead used for both Aspartic Acid (Asp-D) and Asparagine (Asn-N) when it is either unclear or either amino acid may be found in a peptide sequence. Notice that the 3-letter codes for Asp-D are GAC and GAU and the 3-letter codes for Asn-N are AAC and AAU, so these two amino acids that are very close in molecular weight and size are separated in the genetic code by only a single nucleotide mutation between A and G in the first position.
C is for Cysteine, which is also abbreviated by Cys. It is sometimes abbreviated by the symbol Cyz when acting as a deprotonated catalytic residue. Cym also refers to the deprotonated form. Cyx is sometimes used to refer to Cysteine when the thiol is oxidized to form a disulfide derivative. The two sulfur-containing amino acids are more easily oxidized than the other amino acids.
Cysteine is the smallest and simplest of the two sulfur-containing proteinogenic amino acids (encoded by the genetic code). The other sulfur-containing amino acid is Methionine-Met-M.
Cysteine is encoded by the codons UGC and UGU. Notice that these codons are a single first position mutation (U to A) from the codons AGC and AGU which encode the similarly sized amino acid Serine-Ser-S. Also notice that the nearby UGA codon, which is normally described as a stop codon in the standard genetic code, can also encode for the “21st proteinogenic amino acid”, Selenocysteine-Sec-U, which is a modification of Cysteine in which Selenium replaces Sulfur. Additionally, Cysteine codons UGC and UGU are a single second position mutation (G to A) from the codons UAC and UAU which encode the slightly more acidic amino acid Tyrosine-Try-T, which is somewhat hydrophobic like Cysteine.
Of interest, “Cysteine has been proposed as a preventive or antidote for some of the negative effects of alcohol, including liver damage and hangover” is a quote from the wikipedia article on Cysteine. From the same article, Cysteine is important for flavoring food, breaking disulfide bonds in hair perms, and in detecting protein structure or investigating protein folding processes using site-directed spin labeling techniques.