Your body can’t store extra protein in the same way it can store extra carbohydrate (glycogen in muscle and liver) and fat (in fat cells).
The fact we cannot store protein for later use is one of the reasons why we recommend including protein in every meal.
So what happens to this extra protein?
Once your protein needs are met any extra protein consumed is either used as energy or stored as fat.
This requires amino acids (broken down protein) to either be converted into molecules which can be used as energy or into to fatty acids to be stored.
The fate of this extra protein (used for energy or stored as fat) depends on energy balance. For example, if you are in an energy deficit extra protein will be used for energy. If you are in positive energy balance i.e. an energy surplus protein will be stored as fat.