posted on 2020-03-02, 18:24authored bySourav Nandi, Arghajit Pyne, Meghna Ghosh, Pavel Banerjee, Biswajoy Ghosh, Nilmoni Sarkar
One
of the congenital flaws of metabolism, phenylketonuria
(PKU), is known to be related to the self-assembly of toxic fibrillar
aggregates of phenylalanine (Phe) in blood at elevated concentrations.
Our experimental findings using l-phenylalanine (l-Phe) at millimolar concentration suggest the formation of
fibrillar morphologies in the dry phase, which in the solution phase
interact strongly with the model membrane composed of 1,2-diacyl-sn-glycero-phosphocholine (LAPC) lipid, thereby decreasing
the rigidity (or increasing the fluidity) of the membrane. The hydrophobic
interaction, in addition to the electrostatic attraction of Phe with
the model membrane, is found to be responsible for such phenomena.
On the contrary, various microscopic observations reveal that such
fibrillar morphologies of l-Phe are severely ruptured in
the presence of its enantiomer d-phenylalanine (d-Phe), thereby converting the fibrillar morphologies into crushed
flakes. Various biophysical studies, including the solvation dynamics
experiment, suggest that this l-Phe in the presence of d-Phe, when interacting with the same model membrane, now reverts
the rigidity of the membrane, i.e., increases the rigidity of the
membrane, which was lost due to interaction with l-Phe exclusively.
Fluorescence anisotropy measurements also support this reverse rigid
character of the membrane in the presence of an enantiomeric mixture
of amino acids. A comprehensive understanding of the interaction of
Phe with the model membrane is further pursued at the single-molecular
fluorescence detection level using fluorescence correlation spectroscopy
(FCS) experiments. Therefore, our experimental conclusion interprets
a linear correlation between increased permeability and enhanced fluidity
of the membrane in the presence of l-Phe and certifies d-Phe as a therapeutic modulator of l-Phe fibrillar
morphologies. Further, the study proposes that the rigidity of the
membrane lost due to interaction with l-Phe was reinstatedin
fact, increasedin the presence of the enantiomeric mixture
containing both d- and l-Phe.