Proteins (Or the ability to make them) is not requisite for life, nor are nerve impulses, nor is evolution. If we encountered an immortal (Does not evolve), sterile (Does not reproduce), silicon-based alien (No proteins), that would most certainly be heralded as finding extraterrestrial life.

Reasoning about much large systems than our own is difficult. Imagine a bacteria attempting to reason about a human - the existence of fluid transport and centralized heating may seem a bit odd, as bacteria have developed to solve an entirely different class of problems at the organism level.