After conducting research based on the available information, I found that Lipitor primarily binds to HMG-CoA reductase, which is not a protein but an enzyme. HMG-CoA reductase plays a crucial role in the production of cholesterol in the body. Lipitor, a statin drug, works by inhibiting this enzyme, thereby reducing the liver's cholesterol production and increasing the uptake of low-density lipoprotein (LDL) from the bloodstream [1].

For clarification, Lipitor does not directly bind to a protein; instead, it targets an enzyme that plays a significant role in cholesterol synthesis.

Sources:
[1] DrugPatentWatch.com. (n.d.). Lipitor (Atorvastatin) Drug Patent Expiration & Generic Launch Dates. Retrieved from https://www.drugpatentwatch.com/lipitor-atorvastatin-generic-launch-dates/