Protein”s 3d structure and how it can be modified

When spider silk leaves a spider it’s a liquid, but it rapidly converts to a solid when the spider squirts an acidic solution onto the silk (a protein) as it leaves the spider’s body.  Explain, on a molecular level, what happened to the protein-no details-just describe in terms of what we learned in class about protein’s 3D structure and how it can be modified.