Like all plants that produce sugar produce left-handed sugar molecules. And all animals that can digest sugar can only digest left-handed sugar molecules. There was no meeting, this is just the way it worked out.
The meeting was the animals who evolved to not be able to consume this, lived in more harsh conditions than those that had the readily available sugar. Evolution.
Our physiology can still interact with other chiral molecules though right?
Just for example, both the stereoisomers, dextro/levo amphetamine, in my limited understanding of pharmacological interactions, cause a reaction.
One being a powerful stimulant/psychotropic that can cause psychosis, the other benign enough to be sold over the counter as a nasal decongestant with stimulating effects, but orders of magnitude weaker.
You are correct. Protein chirality determines which direction they twist when they fold but the binding sites are all made up of the same functional groups, just arranged differently.
Realistically they have to be compatible because chirality is enforced by a D-handed chiral checkpoint protein that preferentially binds to L-amino acids, excluding the D-amino acids. All living organisms use the “wrong” isomer to make sure only the “right” isomer is used in protein synthesis. The amino acid cysteine is also present in both forms in mammals, so it extends to small molecules too.
