What is the function of this fixed protrusion on the tail?
That is almost certainly a navigation antenna. 

From the E190 AOM (Airplane Operations Manual):  



You can see the VOR2/LOC2 antenna rather more clearly in this photo:  



(The VOR1/LOC1 and VOR3 antennae are embedded within the tailfin.)

Similar nav antennae are used on many smaller aircraft such as (more modern) light aircraft, utility aircraft, business jets and some regional jets.