Methionine and cysteine influence on proteins?

[icakeov]

Hello, I was just wondering what are the distinct features that methionine and cysteine add to proteins when they happen to be in them, as opposed to proteins that contain only non-sulfur-containing amino acids?

I am especially if they create unique conformations for the proteins, that other amino acids don't.

Any thoughts appreciated!

 

[Ygggdrasil]

Cysteine plays a number of important structural roles in proteins that cannot be easily substituted by other amino acids: https://en.wikipedia.org/wiki/Cysteine#Biological_functions

I'm not sure if methionine has any unique roles in protein structure (aside from Met being the start codon).

 

[icakeov]

Great! thanks Ygggdrasil!
I was mainly wondering the introduction of Sulphur does to the overall system.

 

[Ygggdrasil]

It's not really the sulfur that gives cysteine it's special properties (methionine also has a sulfur atom and it can't perform some of the same functions), but rather the presence of a thiol functional group.

 

[icakeov]

Interesting! Thanks.
Are the 20 amino acids contained in all life? Or are there some species that have extra amino acids, with "extensions" like these that create completely different proteins from any other species?

 

[Ygggdrasil]

Some species have extra amino acids like selenocysteine and pyrolysine. I am not aware of any organism that encodes fewer than 20 amino acids, though I would not be surprised if some did. Researchers have re-engineered the genetic code to create organisms that use unnatural amino acids.