Sub-nanometre mapping of the aquaporin-water interface using multifrequency atomic force microscopy

Area of Science:

• Biophysics
• Membrane Protein Research
• Ocular Biology

Background:

• Aquaporins, like aquaporin-0 (AQP0), are crucial for water and small molecule transport across cell membranes.
• AQP0 is vital for water, ion, and metabolite circulation in the eye lens, enabling water flow beyond diffusion limits.
• AQP0's role in lens function and diseases like cataracts underscores the need to understand its interfacial properties.

Purpose of the Study:

• To investigate the interfacial water behavior around AQP0 in its native lattice arrangement.
• To map the AQP0 protein and its surrounding liquid environment with high resolution.
• To elucidate the effect of AQP0's structure and arrangement on water dynamics at the membrane interface.

Main Methods:

• Utilized multifrequency atomic force microscopy (AFM) for high-resolution imaging.
• Employed the fundamental eigenmode of the AFM cantilever to probe interfacial water.
• Used the second eigenmode of the AFM cantilever to analyze the mechanical response and structure of the AQP0 protein.

Main Results:

• Identified a distinct interfacial region around AQP0 tetramers with higher water affinity.
• Achieved sub-nanometer resolution imaging of both the AQP0 protein and the interfacial liquid.
• Obtained sub-molecular details of the protein surface and subsurface structure, correlating AFM modes with observed phenomena.

Conclusions:

• Multifrequency AFM successfully maps interfacial water and AQP0 structure with high resolution.
• A specific water-rich region with increased protein affinity surrounds AQP0 tetramers.
• This study provides new insights into AQP0's role in water transport and its implications for eye lens physiology and disease.