Pma Case Study

Decent Essays
We next studied the effect of PMA alone on A1-40 conformation. As speculated, we observed a PMA directed rapid sheet induction in A1-40 at equimolar concentration at pH 7.4 where A1-40 carries a net charge of -2.9 (Fig 2b). A decrease in the buffer pH from 7.4 to 2.5 reduces the electrostatic interaction between PMA and A1-40 (net charge +6.7) and resulted a random coil A1-40 conformation (Fig 2b, red graphs). Moreover, we observed -helical CD spectra for A1-40 interacting to DMPC nanodiscs at pH=5.5 where A1-40 nearly carries no charge (Fig 2b). Overall the CD results suggested that at physiological pH, the cationic PMA binds strongly to the anionic A1-40 followed by a rapid structural conversion. To understand the role of…show more content…
Binding kinetics of A1-40 and nanodiscs The interactions between A1-40 and nanodiscs was studied using ITC measurements. In reference to our CD results which showed a typical sheet conformation in A1-40 in both zwitterionic and anionic nanodiscs, we measured the binding affinity (Kd) of A1-40 in DMPC (100%) and DMPC mixed with variable percentage of anionic lipids such as DMPG and cardiolipin (CL). A1-40 was observed to induce an intermediate -helix conformation in the presence of anionic lipids such as GM1 and phosphatidylserine and phosphatidylglycerol. Thus, we targeted anionic lipids to examine how the membrane compositions in nanodiscs affect the binding kinetics. As shown in Fig 2b, distinct therograms were obtained for A1-40 (20 M) in the targeted nanodiscs (400 M lipids) containing 85 M PMA. A recent study showed that A1-40 doesn’t bind to zwitterionic membranes using fluorescence titrations [35]. On the other hand, studies have shown that different sizes of zwitterionic liposomes (DPOC and POPC) accelerate A1-40 aggregation significantly at micro-molar concentration [19]. Moreover, we showed in a recent study that zwitterionic lipids such as DLPC accelerates A1-40 aggregation at very low concentrations and also inhibits and remodel fibrillation [33]. Structural studies using NMR and computational methods also
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