[ItsYaBoiGaryOak (OP)]

My goal is to find anything that can stick proteins together. It doesn't matter where or how, just two proteins contently attached.

Transglutaminase bonds glutamine and lysine together, peptidases make peptide bonds.

Is there anything else?

[chiralSPO]

disulfide bonds are a good way to stick cystine-rich proteins together. first reduce them all to SH termination, then you might be able to oxidize them in a high enough concentration to have cross-linking between proteins. You might also use a bis-thiol linker.

[evan_au]

Are there reagents, enzymes, or toxins that bond proteins together?

Just heat them.

The classic example is a boiled egg:
- At room temperature, the proteins in the "white" of the egg form little balls, and they slide over each other easily, forming a viscous fluid.
- Heat it to 100C for 5 minutes, and the proteins denature, and form a tangled knot that is solid and doesn't flow
- Thus binding the proteins together

See: https://en.wikipedia.org/wiki/Denaturation_(biochemistry)