Membrane Accelerator
Background
As there is no compartment in prokaryotic cells, enzymes involved in a biochemical pathway diffuse all over the cytoplasm. Intermediates produced from one enzyme cannot be passed efficiently to the next due to spatial obstacles.
Assemblies of enzymes could help substrates flow by decreasing distance that intermediates have to travel between enzymes, and thus increase yields of sequential biological reactions. If we attach those enzymes to engineered membrane proteins which constitutively assemble together, the reactions are going to proceed much faster.
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Construction
File:12SJTU 2PDZ.gif
File:12SJTU GBD.gif
File:12SJTU SH3.gif
_Fig.1:PDZ domain & ligand __|_Fig.2:GBD domain & ligand _|__Fig.3:SH3 domain & ligand__
___from PDB 2PDZ ____________|______from PDB 1T84_________|_______from PDB 1CKB_________
As demonstrated before, we built our device on E.coli inner membrane protein Lgt. SRP-dependent signaling sequence of DsbA is fused to N-terminus to localize fusion proteins to membrane.
To assemble and arrange enzymes onto inner membrane of E.coli, we incorporate three protein domains that can interact with their cognate ligands. (Dueber, Wu et al. 2009) Protein-protein interaction domains and ligands from metazoan cells (mouse SH3 and PDZ domains and rat GBD domain) were recruited to assemble enzymes on membrane. Each domain could assemble with its cognate ligand.
Fluorescence Complementation Assay
To prove whether our membrane protein equipped with those interacting protein could assemble with each other, we conducted fluorescence complementation assay. (Valencia-Burton, McCullough et al. 2007)
EGFP was split into two halves, named 1EGFP and 2EGFP respectively. If there is interaction between the two proteins which were fused with 1EGFP and 2EGFP, it is expected that fluorescence should be observed. Otherwise, no fluorescence could be observed.
 Fig.5 :Group 1, 2, 3 were designed to test the interaction of SH3domain & ligand, PDZdomain & ligand and GBDdomain & ligand respectively. Proteins within each group were expressed in E.coli. If there exists interaction within membrane proteins of each group, we expected to observe fluorescence on E.coli membrane.
Figure
arabinose concentration
induction time
It is proved that membrane proteins with interacting proteins could interact and dimerize with each other. Thus, by recruiting E.coli native membrane protein Lgt, interacting proteins (SH3, PDZ, GBD) and downstream enzymes, we can easily build a Membrane Accelerator.
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