Imaging of individual concanavalin a proteins by atomic force microscopy

Abstract

Determining the monomolecular structure of lectins, such as concanavalin A (Con A), is crucial for understanding immune recognition mechanisms. However, most current studies focus on the cellular effects of Con A, leaving a gap in the understanding of its individual protein structure. This study uses tapping-mode atomic force microscopy (AFM) to directly visualize individual Con A proteins on mica surfaces. This approach overcomes the limitations of previous cellular-level studies and provides a new method to explore protein substructures at the single-molecule level. We also investigate how varying concentrations of Ni²⁺ (5 mM to 50 mM) influence the surface roughness and protein morphology. Results show that increasing the Ni²⁺ concentration leads to higher roughness and changes in the arrangement of Con A proteins. At 50 mM Ni²⁺, Con A proteins adopt four orientations: tiled, inverted triangular pyramid, vertical, and upright triangular pyramid. In contrast, at 5 mM Ni²⁺, the proteins are primarily arranged in two orientations: tiled and vertical. This work provides an AFM-based imaging method that enables the visualization of individual Con A proteins, offering insights into protein-surface interactions and its applications in protein-based assays.