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.

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

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