Point mutagenesis and cocrystallization of wild-type and mutant proteins: A study of solid-phase coexistence in two-dimensional protein arrays

We are studying the molecular organization of protein arrays using two-dime nsional streptavidin crystals bound to biotinylated lipid monolayers at the air-water interface. We constructed a mutant form of the streptavidin prot ein that successfully alters the molecular organization of the streptavidin crystals. Cocrystallization of streptavidin carrying this single targeted point mutation with wild-type streptavidin yields two-dimensional crystals displaying a chiral morphology with molecular coexistence, indicating a sol id-phase transition. The phase coexistence and resulting morphologies are r eminiscent of two-dimensional crystal behavior of wild-type streptavidin ne ar its isoelectric point, and this analogy is discussed. These results demo nstrate the potential to manipulate protein array formation through point m utagenesis and cocrystallization.