Nexus

The Nexus is the heart of a Protoss base. Unlike most other protoss buildings it can be warped in without a Pylon. It constructs Probes and serves as a processing center for Minerals and Vespene gas.

Psionic Matrix
Protoss structures and units, to a lesser extent, draw their energy from a great psionic energy matrix that emanates from Aiur. While a Nexus provides a link to this matrix, Khaydarin Crystal-based Pylons are needed to actually tap into the energy required to provide psionic energy to new colonies. Each Pylon generates a short-ranged aura of energy, which can provide the power needed by structures and warp gates. If a Protoss building loses its connection to the Psionic Matrix, it will shut down until it is reconnected, and new units cannot be gated in if there is insufficient psionic energy to provide them with power.

Upgrades

 * Plasma Shields