Characterization and Computational Engineering of Structural Elements Controlling Gas Permeability in PIP2;1...

Area of Science:

• Membrane biophysics
• Molecular dynamics simulations
• Protein structure-function relationships

Background:

• Aquaporins (AQPs) are integral membrane proteins facilitating water transport.
• AQPs also conduct small gas molecules like oxygen (O2) and carbon dioxide (CO2).
• The central pore of AQPs is a proposed pathway for gas permeation.

Purpose of the Study:

• To comparatively study gas permeability in plant (SoPIP2;1) and mammalian (bAQP1) aquaporins.
• To elucidate the structural determinants of gas transport through the AQP central pore.
• To understand the molecular basis for differential gas permeability between plant and mammalian AQPs.

Main Methods:

• Comparative molecular dynamics (MD) simulations.
• Utilized flooding simulations, umbrella sampling, and implicit ligand sampling.
• Performed in silico alanine substitution and site-directed mutagenesis.

Main Results:

• Plant SoPIP2;1 exhibits lower gas permeability than mammalian bAQP1.
• Residue Trp79 in SoPIP2;1 forms a major constriction, hindering gas permeation.
• Phe207 in SoPIP2;1 stabilizes the Trp79 constriction; bAQP1 has smaller residues (Leu56, Ala179) at analogous positions, facilitating gas transport.

Conclusions:

• Specific amino acid residues, particularly Trp79 and Phe207 in SoPIP2;1, dictate central pore constriction and control gas permeability.
• The replacement of bulky residues with smaller ones in bAQP1 explains its higher gas permeability.
• Engineering bAQP1 with plant-like residues (Trp, Phe) significantly reduces its gas permeability.