Scientists Directly Visualize the Hidden Water Structure Around Proteins for the First Time

An international team of researchers from Japan, Finland, Italy and the United States has produced the first direct three-dimensional images of the water structure that surrounds peptides, the building blocks of proteins. Published in the journal Nature Communications, the study used an advanced imaging method called three-dimensional atomic force microscopy (3D-AFM) to map the water at subnanometer resolution, working with a self-assembled peptide called GrBP5-WT placed on a graphite surface.

The images show that water near peptide surfaces is not a passive solvent. It forms highly organized, multilayered structures shaped by the underlying amino acid sequence and surface chemistry. These hydration layers extend several layers out from the peptide surface and carry distinct patterns linked to hydrophobic, polar, aromatic and charged amino acids, creating what the researchers call a hydration fingerprint.

"Our findings suggest that proteins cannot be fully understood by sequence and structure alone," said Professor Mehmet Sarikaya of the University of Washington. He and his colleagues propose a new concept, the "protein superstructure": the protein together with its uniquely organized hydration architecture. "A protein never exists in isolation," said Dr. Takeshi Fukuma of Kanazawa University. "It exists together with its hydration architecture."

The researchers say the study does not propose a new form of "biological water," but shows that interfacial water forms dynamic, sequence-dependent structures imposed by the peptide's surface chemistry. "Directly visualizing that hidden architecture opens an entirely new dimension in protein science," said Dr. Ayhan Yurtsever, one of the study's authors. The team said future work would extend the measurements to more complex proteins and biological systems.