A/T Shift Lock System: Description
WARNING: This page is about a different car, the 2008 Infiniti M45 and 2008 Infiniti M35. However, it is still accessible from the selected car via links, so may be relevant.
The mechanical key interlock mechanism also operates as a shift lock:
With the ignition switch turned to ON, the selector lever cannot be shifted from "P" position to any other positions unless the brake pedal is depressed.