Pyrrolysine
Pyrrolysine is a naturally-occurring, genetically encoded amino acid, sometimes called the "22nd amino acid". For more information, please see Pyrrolysine in Wikipedia.
OccurrenceOccurrence
Some proteins in methanogenic archaea include pyrrolysine (Pyl). Methanosarcina barkeri monomethylamine methyltransferase (MtmB, 1nth, 1l2q) was the first identified structure containing this amino acid, and in the crystal structure it is identified as BGX, with the rest of the amnio acid identified as LYS202[1]. Chemically modified forms of pyrrolysine are present in the MtmB structures 1tv2, 1tv3, and 1tv4[2]. The PDB also contains several structures for pyrrolysyl-tRNA synthetase, including 2zce which includes pyrrolysine designated PYH.