Why do the standard amino acids that occur in proteins not form intramolecular amide bonds?
revernance asked:
Beta-Amino acids can form an intramolecular amide bond, which results in the formation of the four-membered Beta-Lactam ring. This structure is the characteristic feature of Beta Lacta antibiotics, such as penicillin.
Beta-Amino acids can form an intramolecular amide bond, which results in the formation of the four-membered Beta-Lactam ring. This structure is the characteristic feature of Beta Lacta antibiotics, such as penicillin.
Well, being a beta lactam ring, it’s very strained, requiring a lot of energy put in to make the reaction happen. In a more typical scenario, the ribosome structure simply doesn’t allow the right conformation to make intramolecular amide bonds. Besides, stuff like penicillin isn’t make enzymatically, but using very specific organic methods.
However, that isn’t to say that amino acids don’t naturally undergo intramolecular condensations. Some organisms possess enzymes capable of making things like oxazole and thiazole rings (5 member), an intramolecular serine/threonine or cysteine condensation. These go on to form molecules that the organism probably excretes to kill other stuff. (telomestatin is an example off my head). as for amide bonding lysines/arginines, I’m sure there are examples of this, but I can’t remember. Then again, even if they are to condense, if I’m counting properly, they shouldn’t be forming 4 member rings…