Xx. Chen et al., Engineering oriented heme protein maquette monolayers through surface residue charge distribution patterns, J PHYS CH B, 103(42), 1999, pp. 9029-9037
We have designed and synthesized four-alpha-helix-bundle proteins that acco
mmodate heme groups to act as molecular "maquettes" of more complex natural
electron-transfer proteins. These bundles can be oriented at an air-water
interface and transferred onto solid surfaces to facilitate the exploration
of the factors that govern biological electron transfer. We find that the
orientation of these maquettes on an air-water interface can be controlled
by choosing the distribution of charged amino acids along the sides of the
helices exposed to water. The four alpha-helices were assembled either as t
wo subunits, where each subunit consists of two alpha-helices linked by a t
erminal cysteine disulfide bond, or as a single, four-helix covalent unit c
onsisting of two helix-loop-helix molecules linked by a terminal cysteine.
In either case, when each alpha-helix contains both positively charged lysi
nes and negatively charged glutamates, addition of the heme binding bundles
to an air-water interface causes them to open up and lie on the surface wi
th alpha-helical axes oriented parallel to the interface. In contrast, when
the positive and negative charges are segregated on different helices (two
negative, two positive) of the single covalent four-alpha-helix-bundle uni
t, the bundle preserved its integrity on transfer to the air-water interfac
e. Moreover, the presence of heme dictates the orientation of the alpha-hel
ical axes of the bundle with respect to the surface plane. The alpha-helice
s adopt a parallel orientation in the absence of heme and a perpendicular o
rientation in the presence of heme. Circular dichroism (CD) and ultraviolet
-visible (UV-vis) spectroscopy supported by linear dichroism demonstrate th
at these molecular orientations are preserved in Langmuir-Blodgett monolaye
r films on solid substrate surfaces.