A door operator system for moving a door of a vehicle between open and closed positions includes a track defined in a base, the track having a curved portion at an end thereof; a drive bracket configured to suspend the door from the base, the drive bracket being slidably movable along the track between an open position and a closed position adjacent to the curved portion; a drive mechanism configured to cause movement of the drive bracket between the open and closed positions; and a locking system configured to retain the drive bracket in the closed position. When the drive bracket is in the closed position, the curved portion engages a cam follower of the locking system to retain the cam follower in a locked position that is over center with respect to a plane perpendicular to the track and a plane parallel to the track.