I want to utilize protein-protein interaction knowledge (Human) for my analysis. I find there are many databases provide such information, such as BioGRID, STRING, HPRD, PINA. The problem is that the interaction information from these databases differ a lot. For example by querying APP, it returns 1975 interactors from BioGRID, while by STRING only 10 interactors. Another example that querying ZPBP2 it returns 10 interactors from both BioGRID and STRING, but with 0 overlap. For those who have experience in protein interaction analysis, can you provide some suggestions?