Effect of compressive force on unbinding specific protein-ligand complexes with force spectroscopy

Cross-reactivity between myelin oligodendrocyte glycoprotein and human endogenous retrovirus W protein: nanotechnological evidence for the potential trigger of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune and inflammatory demyelinating disease of the central nervous system. Experimental evidence supports the reactivity of autoantibodies against components of myelin sheath including the myelin oligodendrocyte glycoprotein (MOG). The MS etiology is still unknown, but some risk factors associated with immune dysregulation, genetic susceptibility, and environmental factors are under investigation. The last consider the hypothesis of molecular mimicry mechanism, which is potentially triggered by viral antigen inducing MS autoimmunity. The Human Endogenous Retroviruses W family (HERV-W) is the subject of studies within this field, based on the detection of HERV-W envelope gene proteins in MS patients' samples. In the biomedical field of diagnosis and therapeutics, nanotechnology is of great use for the detailed study of molecular mechanisms involving specific interactions between biomolecules providing high specificity and sensitivity of response. In view of the significance of etiological aspects for the comprehension of MS mechanisms of action, we applied a nanotechnological approach designed for antibody detection. For this, we analyzed MOG peptide sequences similar to the HERV-W protein. These sequences were subjected to interaction with anti-HERV-W antibodies using atomic force spectroscopy (AFS) and silver nanoparticles (AgNPs) methods to survey the potential occurrence of molecular mimicry. Our results revealed the molecular recognition between the anti-HERV-W antibody and the HERV-W and MOG epitopes by AFS and AgNPs approaches. Specific non-linear shape of force curves and median adhesion force values within the expected range for an antigen-antibody interaction were obtained for HERV-W and MOG peptides, 163 pN and 178 pN, respectively, suggesting the occurrence of cross-reactivity in these systems.

Nanomechanical and Thermophoretic Analyses of the Nucleotide-Dependent Interactions between the AAA(+) Subunits of Magnesium Chelatase

In chlorophyll biosynthesis, the magnesium chelatase enzyme complex catalyzes the insertion of a Mg(2+) ion into protoporphyrin IX. Prior to this event, two of the three subunits, the AAA(+) proteins ChlI and ChlD, form a ChlID-MgATP complex. We used microscale thermophoresis to directly determine dissociation constants for the I-D subunits from Synechocystis, and to show that the formation of a ChlID-MgADP complex, mediated by the arginine finger and the sensor II domain on ChlD, is necessary for the assembly of the catalytically active ChlHID-MgATP complex. The N-terminal AAA(+) domain of ChlD is essential for complex formation, but some stability is preserved in the absence of the C-terminal integrin domain of ChlD, particularly if the intervening polyproline linker region is retained. Single molecule force spectroscopy (SMFS) was used to determine the factors that stabilize formation of the ChlID-MgADP complex at the single molecule level; ChlD was attached to an atomic force microscope (AFM) probe in two different orientations, and the ChlI subunits were tethered to a silica surface; the probability of subunits interacting more than doubled in the presence of MgADP, and we show that the N-terminal AAA(+) domain of ChlD mediates this process, in agreement with the microscale thermophoresis data. Analysis of the unbinding data revealed a most probable interaction force of around 109 pN for formation of single ChlID-MgADP complexes. These experiments provide a quantitative basis for understanding the assembly and function of the Mg chelatase complex.

Specific binding at the cellulose binding module-cellulose interface observed by force spectroscopy

The need for effective enzymatic depolymerization of cellulose has stimulated an interest in interactions between protein and cellulose. Techniques utilized for quantitative measurements of protein-cellulose noncovalent association include microgravimetry, calorimetry, and atomic force microscopy (AFM), none of which differentiate between specific protein-cellulose binding and nonspecific adhesion. Here, we describe an AFM approach that differentiates nonspecific from specific interactions between cellulose-binding modules (CBMs) and cellulose. We demonstrate that the "mismatched" interaction between murine galectin-3, a lectin with no known affinity for cellulose, and cellulose shows molecular recognition force microscopy profiles similar to those observed during the interaction of a "matched" clostridial CBM3a with the same substrate. We also examine differences in binding probabilities and rupture profiles during CBM-cellulose binding experiments in the presence and absence of a blocking agent-a substrate specific for CBM that presumably blocks binding sites. By comparison of the behavior of the two proteins, we separate specific (i.e., blockable) and nonspecific adhesion events and show that both classes of interaction exhibit nearly identical rupture forces (45 pN at ∼0.4 nN/s). Our work provides an important caveat for the interpretation of protein-carbohydrate binding by force spectroscopy; delineation of the importance of such interactions to other classes of binding warrants further study.

A guide into glycosciences: How chemistry, biochemistry and biology cooperate to crack the sugar code

BACKGROUND

The most demanding challenge in research on molecular aspects within the flow of biological information is posed by the complex carbohydrates (glycan part of cellular glycoconjugates). How the 'message' encoded in carbohydrate 'letters' is 'read' and 'translated' can only be unraveled by interdisciplinary efforts.

SCOPE OF REVIEW

This review provides a didactic step-by-step survey of the concept of the sugar code and the way strategic combination of experimental approaches characterizes structure-function relationships, with resources for teaching.

MAJOR CONCLUSIONS

The unsurpassed coding capacity of glycans is an ideal platform for generating a broad range of molecular 'messages'. Structural and functional analyses of complex carbohydrates have been made possible by advances in chemical synthesis, rendering production of oligosaccharides, glycoclusters and neoglycoconjugates possible. This availability facilitates to test the glycans as ligands for natural sugar receptors (lectins). Their interaction is a means to turn sugar-encoded information into cellular effects. Glycan/lectin structures and their spatial modes of presentation underlie the exquisite specificity of the endogenous lectins in counterreceptor selection, that is, to home in on certain cellular glycoproteins or glycolipids.

GENERAL SIGNIFICANCE

Understanding how sugar-encoded 'messages' are 'read' and 'translated' by lectins provides insights into fundamental mechanisms of life, with potential for medical applications.