This is really more a question of semantics. There are signaling peptides that are only a few amino acids, or even a single amino acid, but they lack well-defined secondary or tertiary structure. One of the smallest, if not the smallest, folded protein is the villin headpiece. read more
There are signaling peptides that are only a few amino acids, or even a single amino acid, but they lack well-defined secondary or tertiary structure. One of the smallest, if not the smallest, folded protein is the villin headpiece. read more
A rare exception to the dominance of α-amino acids in biology is the β-amino acid beta alanine (3-aminopropanoic acid), which is used in plants and microorganisms in the synthesis of pantothenic acid (vitamin B 5), a component of coenzyme A. D-amino acid natural abundance. D-isomers are uncommon in live organisms. read more