Integrin alpha2beta1 is a potential target molecule in drug development. We have established "design" criteria for molecules that bind to the "closed" conformation of alpha2I domain via Mg(2+) in MIDAS (metal ion dependent adhesion site) while simultaneously forming interactions with neighboring amino acid residues. Specific tetracyclic Streptomyces products belonging to the group of aromatic polyketides fulfill our criteria and inhibit alpha2beta1 integrin. All previously described inhibitors of alphaI domain integrins act in an allosteric manner.