The paraoxanase1 (PON1) enzyme is always found bound to high-density lipoprotein (HDL)  particles, and its primary biological function appears to be hydrolyzing lactones produced during lipid oxidation.  It also inactivates a variety of organophosphates (OP), including nerve agents, through hydrolyses.  However, the mechanism of nerve agent inactivation by PON1 has not been established.  No one has been able to successfully crystallize human PON1 (hPON1).  On the other hand, a recombinant PON1 (rePON1) protein has been produced that will crystallize, and a structure was recently published (PDB code: 3SRG).  The sequence identity between hPON1 and RePON1 was about 86%.  Our interest is in determining in what ways the rePON1 structure deviates from the hPON1 structure and especially in determining how the interaction of the hPON1 with the lipids of the HDL affects the enzyme's structure.           Using homology modeling we have modeled the 3D structure of hPON1 by using 3SRG as a reference template.  Residues 1-18 (the H1 loop), which insert into the HDL and which are missing in the rePON1, were rebuilt.  The protein was aligned along the z-axis and the H1 loop was immersed into a lipid (POPC) and cholesterol bilayer. The protein and membrane-cholesterol bilayer was then capped with explicit water molecules.  Afterwards, the entire system was equilibrated for 50 ns using Amber12 and the ff12SB force field.       One common, biologically relevant polymorphism is present in hPON1, the Q192R polymorphism.  To study this, the structure was taken after 30 ns of equilibration, and Q192 was mutated to R192.  The R192 system was equilibrated for another 20 ns.   The structural differences between the two models and RMS fluctuations vs. time for various loops will be presented in this poster.

Effects of lipid binding on the structure of human paraoxanase1

245th National Meeting (2013)

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