Nothing. If they fold well and are water soluble, the solution remains transparent because the protein remains solvated. If they don't fold well, they expose hy

Nothing. If they fold well and are water soluble, the solution remains transparent because the protein remains solvated. If they don't fold well, they expose hydrophobic regions that then bind to the hydrophobic regions on neighboring proteins, causing a chain reaction that results in a solid chunk of protein that isn't dissolved. Not all proteins are water soluble in nature, however. Plenty of membrane proteins and other proteins exist that don't fold well when expressed in a micro-organism.