The gran turismo model of the 535i means that it's a 5-door fastback version of previous 5-series model ranges. Fastback refers to the style of the back of the vehicle, where the car has a slope from the roof to the rear bumper. Gran turismo models have had the option of a turbocharged petrol engine, straight 6-diesel engine, or V8 petrol engine. The 535i was a part of the sixth generation of the BMW series that was in production from 2010-2017.
When you need to make repairs on your 535i GT, which you will have to do at some point with any car you drive, you'll want to make sure you're getting only the best OEM parts for the job. Quality can suffer greatly when you're shopping for aftermarket parts, because they are mass produced and the specific model that you drive is not considered in the production process. OEM parts almost always come with a one-year warranty, and OEM parts are guaranteed to be of the same quality that your original BMW parts were. This can save you a lot of time and headache when shopping for parts, because you don't have to second guess if they'll fit.