Can you describe what happens when milk is converted into curd or yoghurt, from your understanding of proteins?
Microorganisms like lactobacillus, secrete lactic acid which changes the pH of milk and proteins, are very sensitive to change in pH. So this pH change due to lactic acid leads to the destruction of secondary and tertiary structures of protein (called denaturation), which leads to precipitation of milk proteins and curd formation.
Milk has many globular proteins. Milk is converted into curd or yoghurt by the action of bacteria.