High Resolution 3D Epitope Mapping Services. Antibody-Antigen 3D Structure Determination.

Why Choose X-ray Crystallography for High-Resolution 3D Epitope Mapping?

Epitope mapping is central to therapeutic monoclonal antibody (mAb) development, as it is essential for analyzing the antibody’s mode of action, including its interactions with the antigen. It has also been noted by Deng et al. (2017) that the quality, conformation, and resolution of epitope residue data can influence the breadth and strength of mAb patents and are essential for strengthening patent protection and overcoming potential challenges in patenting mAbs.

An important consideration is the type of epitope being studied. Epitopes are generally categorized into two main types: linear and conformational epitopes. Linear epitopes consist of short, continuous sequences of amino acids. In contrast, conformational epitopes are derived from the protein’s three-dimensional structure and do not have to form a continuous sequence within the antigen. Different epitope mapping techniques are used depending on the epitope type (Dang et al., 2023). Traditionally, epitopes are examined by hydrogen/deuterium exchange mass spectrometry (HDX-MS) or chemical cross-linking mass spectrometry (XL-MS). Several computational approaches for epitope prediction have also been developed.

While X-ray crystallography (and even cryo-EM) is regarded as the gold standard for high-resolution 3D epitope mapping, there are common misconceptions that the method is too expensive, too time-consuming, requires a large amount of material, or that crystals of mAbs in complex with the antigen are impossible to obtain. It is true that obtaining crystals of an antibody-antigen complex, or of any other protein or protein complex, can be challenging. However, new crystallization techniques that help address many of the method’s problems are continuously being developed. Additionally, crystallization generally does not take long, enabling quick analysis and assessment of the experimental results. Once crystals are obtained, collecting X-ray data and determining the structure are now more straightforward thanks to recent advancements in synchrotron technology (see our blog post on industrial synchrotron crystallography). Even cryo-EM has undergone a major technical overhaul, leading to breakthroughs in the resolution and speed of structure determination for samples that are challenging for X-ray crystallography.

The advances in cryo-EM and X-ray crystallography instrumentation have greatly reduced costs and accelerated the determination of high-resolution structures of proteins and protein-ligand complexes. This is demonstrated by the growth of the Structural Antibody Database (SabDab), which houses over 10,000 antibody structures and 9936 tertiary structures of antibody-antigen complexes determined by X-ray crystallography and cryo-EM. Of these (March 2026), 6,570 structures were determined using X-ray crystallography, 3,945 using Cryo-Electron Microscopy, and 17 by NMR spectroscopy. Out of the X-ray crystallographic structures analyzed, 3,773 (57%) exhibited a resolution better than 3.0 Å, while 1,172 structures had a resolution exceeding 2.0 Å (18%). For cryo-EM structures, 1,475 had a resolution better than 3.0 Å (37%), and 397 structures achieved a resolution exceeding 2.0 Å (10%). The statistics clearly demonstrate the usefulness of these methods, which provide the most accurate, high-resolution insights into antibody-antigen interactions and detailed 3D epitope and paratope mapping. We should also note that these structures can reveal possible conformational changes and allosteric effects that occur during the formation of an antibody-antigen complex, which are very difficult to observe using traditional methods. Needless to say, all this information may significantly enhance antibody targeting.

For more details, please see our blog post on 3D epitope mapping techniques. See also the case studies described below, which include client projects with antibody-antigen complex structures determined at high resolution by the SARomics team using X-ray crystallography and published in high-impact journals. You may also visit our publications page, which showcases 8 Nature papers and over 10 additional publications in other high-impact journals.