The Protectobots' headquarters is an Autobot base from the Generation 1 continuity family.

So then Optimus Prime said: "Protectobots, transform and move out!"

The Protectobots' headquarters serves as the base of operations for the Protectobots. It is located in an unknown city and disguised as an inconspicuous apartment building with a billboard advertising for E Cola on top. The streetside wall can open to let the Protectobots in or out. To keep in touch with Autobot Headquarters safely, the Protectobots' headquarters houses equipment that is uniquely capable of receiving messages on a sub-frequency range.

Fiction

The Transformers cartoon

It'll look more comfy once they've put some beanbags in.

On receiving a request to evacuate civilians ahead of an Autobot assault on the Insecticon army, the Protectobots rolled out of a building that was, we presume, their headquarters. The Revenge of Bruticus

When Megatron was preparing to deploy a moon-blasting cannon, the Protectobots received a request for assistance from Autobot Headquarters. They left their base to go kick Bruticus's tailpipe. B.O.T.

Notes

• As in most such cases, the apparent proximity of this city to Autobot Headquarters presumably makes it another "appearance" of Central City.