Is excess protein converted and stored as body fat?

I am not a nutritionist, but I have been a personal trainer for over 10 years, have a Master of Science degree and have taken several nutrition classes and seminars/conferences on nutrition. I have always understood that any excess calories are stored as fat. Recently, I got into a discussion with a new gym member who has had success with weight loss through a high protein diet--he insists that the body utilizes all protein, no matter if it exceeds calorie output. I have been researching protein specifically, if it actually is converted/stored as fat, and have not found any solid research results. Are there any Registered Dieticians or Nutritionists who can answer this question?