>>16771649
>It’s the same thing as enzymatic promiscuity...It’s all incidental
Enzymes and other functional proteins are incredibly complex molecular machines that must be very precisely built to do anything they do.
Let's go back to chitinase as an example. Human chitinase is purpose‑built piece of nanomachinery for cutting chitin's β‑1,4 links. It needs extremely precise construction to do this.
First it grips a single chitin chain inside a deep, aromatic‑lined groove and flat rings from tryptophan/tyrosine side chains clamp several sugars into ordered subsites, centering the bond to be cut.
The sugar sitting at −1 is then forced out of what might be compared chemically to a comfy chair shape into a strained, transition‑state‑like conformation which prepares the bond for chemical action.
Next the catalytic D‑x‑D‑x‑E motif goes to work: the Glu acts as a general acid, protonating the glycosidic oxygen so the +1 sugar can depart. In the same instant, the carbonyl oxygen of the −1 sugar's own 2‑acetamido group, precisely oriented and polarized by the neighboring Asp residues, attacks the anomeric carbon, forming an oxazolinium intermediate.
Next, that same Glu switches to a general base, activates a tightly positioned water, and the resulting hydroxide strikes C1, collapsing the intermediate and finishing the cut. A tiny product sugar diffuses out; the remaining polymer (or a newly bound segment) is positioned for the next cycle along the same aromatic track.
Every move depends on angstrom‑level distances and angles: the acids must be close enough to hand off protons on cue, the -1 pocket must impose exactly the right distortion, the catalytic water must sit at the right spot and approach from the right angle, etc.
This is a customized machine. This is as absolutely and hopelessly impossible for a random protein sequence to hope to just happen upon as a microchip with 4chan's source code in silicon and copper ores.
