1 research outputs found
Membrane-Induced p<i>K</i><sub>a</sub> Shifts in <i>wt</i>-pHLIP and Its L16H Variant
The pH (low) insertion peptides (pHLIPs)
is a family of peptides
that are able to insert into a lipid bilayer at acidic pH. The molecular
mechanism of pHLIPs insertion, folding, and stability in the membrane
at low pH is based on multiple protonation events, which are challenging
to study at the molecular level. More specifically, the relation between
the experimental p<i>K</i> of insertion (p<i>K</i><sup>exp</sup>) of pHLIPs and the p<i>K</i><sub>a</sub> of the key residues is yet to be clarified. We carried out a computational
study, complemented with new experimental data, and established the
influence of (de)protonation of titrable residues on the stability
of the peptide membrane-inserted state. Constant-pH molecular dynamics
simulations were employed to calculate the p<i>K</i><sub>a</sub> values of these residues along the membrane normal. In the <i>wt</i>-pHLIP, we identified Asp14 as the key residue for the
stability of the membrane-inserted state, and its p<i>K</i><sub>a</sub> value is strongly correlated with the experimental p<i>K</i><sup>exp</sup> measured in thermodynamics studies. Also,
in order to narrow down the pH range at which pHLIP is stable in the
membrane, we designed a new pHLIP variant, L16H, where Leu in the
16th position was replaced by a titrable His residue. Our results
showed that the L16H variant undergoes two transitions. The calculated
p<i>K</i><sub>a</sub> and experimentally observed p<i>K</i><sup>exp</sup> values are in good agreement. Two distinct
p<i>K</i><sup>exp</sup> values delimit a pH range where
the L16H peptide is stably inserted in the membrane, while, outside
this range, the membrane-inserted state is destabilized and the peptide
exits from the bilayer. pHLIP peptides have been successfully used
to target cancer cells for the delivery of diagnostics and therapeutic
agents to acidic tumors. The fine-tuning of the stability of the pHLIP
inserted state and its restriction to a narrow well-defined pH range
might allow the design of new peptides, able to discriminate between
tissues with different extracellular pH values