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 Langm uir-Blodgett (LB) technique. These LB heme protein films were characte rized by circular dichroism (CD), ultraviolet-visible (UV-vis), and Fo urier transformed infrared (FTIR) spectroscopy. During the formation o f monolayer films on substrate, the (alpha ss alpha)(2) heme proteins dissociate into their assa subunits, but remain alpha-helical and reta in the bis-histidine heme ligation. The alpha-helices are oriented in the film close to parallel to the substrate plane and the heme macrocy cle planes are tilted at 40 degrees. There is no detectable ordering o f the molecules in the plane of the monolayer. However, when the loop region was palmitoylated to confer amphiphilic character to the heme p roteins, a profound change of state at high surface pressure was displ ayed. Transfer of this high-pressure film onto solid substrate also ge nerates a film with alpha-helices near 0 degrees and hemes planes at 4 0 degrees, but with added order: remarkably the alpha-helices and one heme edge assume a strong orientation parallel to the direction of wit hdrawal of the substrate from the LB subphase.