Molecular orientation of Langmuir-Blodgett films of designed heme protein and lipoprotein maquettes

De novo designed tetra-alpha-helical heme proteins (alpha ss alpha)(2), comprising two identical helix-loop-helix subunits, alpha ss alpha, were immobilized as monolayer films on solid substrate using the Langmuir-Blodgett (LB) technique. These LB heme protein films were characterized by circular dichroism (CD), ultraviolet-visible (UV-vis), and Fourier transformed infrared (FTIR) spectroscopy. During the formation of monolayer films on substrate, the (alpha ss alpha)(2) heme proteins dissociate into their assa subunits, but remain alpha-helical and retain the bis-histidine heme ligation. The alpha-helices are oriented in the film close to parallel to the substrate plane and the heme macrocycle planes are tilted at 40 degrees. There is no detectable ordering of the molecules in the plane of the monolayer. However, when the loop region was palmitoylated to confer amphiphilic character to the heme proteins, a profound change of state at high surface pressure was displayed. Transfer of this high-pressure film onto solid substrate also generates a film with alpha-helices near 0 degrees and hemes planes at 40 degrees, but with added order: remarkably the alpha-helices and one heme edge assume a strong orientation parallel to the direction of withdrawal of the substrate from the LB subphase.