Molecular Recognition Force Spectroscopy Study of the Specific Lectin and Carbohydrate Interaction in a Living Cell

AFM reveals differential effects of acidification on LDL- and oxidized LDL-receptor interactions: biomechanical implications in atherogenesis

The receptor recognition and interaction of plasma lipoproteins (e.g., native low-density lipoproteins (LDL)/oxidized low-density lipoproteins (oxLDL), as well as the influence of microenvironmental/lysosomal acidification, play critical roles in lipoprotein metabolism and diseases (e.g., atherosclerosis) but have been less investigated. Here, the recognition/interaction of LDL or oxLDL with LDL receptor (LDLR) or CD36 (a scavenger receptor) or with living cells at various pHs was evaluated mainly via atomic force microscopy (AFM). To improve force measurement accuracy, a novel, micro-droplet-based method for AFM probe functionalization was developed. We found that solution acidification significantly reduced the LDL-LDLR binding at pH ≤ 6.4, whereas the oxLDL-CD36 binding had no significant change until pH ≤ 4.4. Compared with a traditional immersion method, our micro-droplet method for AFM probe functionalization produced more accurate interaction forces, and revealed that acidification significantly reduced the LDL-LDLR/cell interaction forces, instead of the oxLDL-CD36/cell-specific interaction forces and nonspecific interaction forces. The data imply that the LDL-LDLR/cell recognition and interaction are susceptible to acidification, whereas the oxLDL-CD36/cell recognition and interaction are tolerant of acidification. The results may provide important novel information and biomechanical/pathological implications for understanding lipoprotein metabolism and atherosclerosis.

Nanoscale clustering of mycobacterial ligands and DC-SIGN host receptors are key determinants for pathogen recognition

The bacterial pathogen Mycobacterium tuberculosis binds to the C-type lectin DC-SIGN (dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin) on dendritic cells to evade the immune system. While DC-SIGN glycoconjugate ligands are ubiquitous among mycobacterial species, the receptor selectively binds pathogenic species from the M. tuberculosis complex (MTBC). Here, we unravel the molecular mechanism behind this intriguing selective recognition by means of a multidisciplinary approach combining single-molecule atomic force microscopy with Förster resonance energy transfer and bioassays. Molecular recognition imaging of mycobacteria demonstrates that the distribution of DC-SIGN ligands markedly differs between Mycobacterium bovis Bacille Calmette-Guérin (BCG) (model MTBC species) and Mycobacterium smegmatis (non-MTBC species), the ligands being concentrated into dense nanodomains on M. bovis BCG. Upon bacteria-host cell adhesion, ligand nanodomains induce the recruitment and clustering of DC-SIGN. Our study highlights the key role of clustering of both ligands on MTBC species and DC-SIGN host receptors in pathogen recognition, a mechanism that might be widespread in host-pathogen interactions.

Investigating biomolecular recognition at the cell surface using atomic force microscopy

Probing the interaction forces that drive biomolecular recognition on cell surfaces is essential for understanding diverse biological processes. Force spectroscopy has been a widely used dynamic analytical technique, allowing measurement of such interactions at the molecular and cellular level. The capabilities of working under near physiological environments, combined with excellent force and lateral resolution make atomic force microscopy (AFM)-based force spectroscopy a powerful approach to measure biomolecular interaction forces not only on non-biological substrates, but also on soft, dynamic cell surfaces. Over the last few years, AFM-based force spectroscopy has provided biophysical insight into how biomolecules on cell surfaces interact with each other and induce relevant biological processes. In this review, we focus on describing the technique of force spectroscopy using the AFM, specifically in the context of probing cell surfaces. We summarize recent progress in understanding the recognition and interactions between macromolecules that may be found at cell surfaces from a force spectroscopy perspective. We further discuss the challenges and future prospects of the application of this versatile technique.

Molecular recognition force spectroscopy study of the dynamic interaction between aptamer GBI-10 and extracellular matrix protein tenascin-C on human glioblastoma cell

Molecular recognition force spectroscopy (MR-FS) was applied to investigate the dynamic interaction between aptamer GBI-10 and tenascin-C (TN-C) on human glioblastoma cell surface at single-molecule level. The unbinding force between aptamer GBI-10 and TN-C was 39 pN at the loading rate of 0.3 nN sec⁻¹. A series of kinetic parameters concerning interaction process such as the unbinding force f(u) , the association rate constant k(on) , dissociation rate constant at zero force k(off) , and dissociation constant K(D) for aptamer GBI-10/TN-C complexes were acquired. In addition, the interaction of aptamer GBI-10 with TN-C depended on the presence of Mg²⁺. This work demonstrates that MR-FS can be used as an attractive tool for exploring the interaction forces and dynamic process of aptamer and ligand at the single-molecule level. As a future perspective, MR-FS may be used as a potential diagnostic and therapeutic tool by combining with other techniques.