(633i) Morphological and in Vitro Functional Investigation of Phospholipid-Membrane Associated Protein (PS I)

Morphological and in vitro functional
investigation of phospholipid-membrane
associated protein (PS I)

Hanieh Niroomand,
Sustainable Energy Education and Research Center (SEERC), Department of
Chemical and Biomolecular Engineering, University of
Tennessee, Knoxville, TN

Dibyendu Mukherjee, Sustainable
Energy Education and Research Center (SEERC), Department of Mechanical,
Aerospace and Biomedical Engineering; Department of Chemical and Biomolecular Engineering, University of Tennessee,
Knoxville, TN

Bamin Khomami, Sustainable Energy
Education and Research Center (SEERC), Department of Chemical and Biomolecular Engineering, University of Tennessee,
Knoxville, TN

Membrane protein structural and in-vitro
functional studies rely on synthetic membrane mimics (e.g., detergents and
liposomes) to stabilize the protein fold and maintain function¹. Our
recent investigations² on the cyanobacterial photosynthetic membrane protein complex, Photosystem I
(PS I), reveal that the two prototypical non-ionic detergents,
n-Dodecyl-β-D-Maltoside (DM) and Triton X-100
(TX-100) can uniquely tailor the solution phase PS I-PS I  interactions/aggregations via the  relative PS I/detergent concentrations³.
In the present study, we use in-situ
dynamic light scattering (DLS) and electron microscopy experiments to investigate
the solution-phase aggregation dynamics of PS
I complex reconstituted
into the phospholipid vesicle diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) for different
phospholipid concentrations. Specifically, two well-established transmission electron microscopy (TEM)
techniques⁴, namely negative staining and direct imaging in cryogenic conditions (cryo-TEM),
are utilized. These measurements reveal the complex morphology
arising out of the interactions of the phospholipid small
unilamellar (SUV) and large unilamellar
vesicles (LUV) with the PS I complexes. In
this presentation, the shape evolution of PS I with respect to lipid vesicle,
and its connection to PS I-PS I as well as PS I-lipid interactions in colloidal
solutions are discussed. Furthermore, new approaches for
incorporation of the PS
I complex into phospholipid liposomes with various
head groups and hydrophobic tails are highlighted. Such information is valuable
in mimicking the naturally occurring protein-phospholipid interactions in cell
membranes. In future, these bio-mimetic systems shall facilitate easy
incorporation of these protein-lipid complexes into novel bio-hybrid devices.

1.      Dewald A.H., Hodges J.C., Columbus L. Biophys J. 2011; 100(9): 2131?2140.

2.     
Mukherjee
D, May M, Khomami B. J. Colloid Interface Sci. 2011;358(2):477-484.

3.     
Mukherjee
D, May M, Vaughn M, Bruce BD, Khomami B. Langmuir. 2010;26(20):16048-16054.

4.     
Gennis
R.B. Biomembranes molecular structure and function.
Springer-Verlag, 1989.