You can analyze your structure on ePISA https://www.ebi.ac.uk/pdbe/pisa/ to look at the various parameters of the interfaces, e.g. buried surface area, hydrophobicity, number of hydrogen bonds, list of residues/atoms involved in the interface, predicted interaction energy and compare this to the values obtained for other complexes.

PDBsum https://www.ebi.ac.uk/thornton-srv/databases/pdbsum/ offers a precalculated summary of the properties of structures deposited in the protein database.

Thanks for your reply, Annemarie. Regarding the analysis you mentioned (buried surface area, hydrophobicity, number of hydrogen bonds, list of residues/atoms involved in the interface, and predicted interaction energy) from PDBsum, which references or criteria are used to interpret these values?. Specifically, is it possible to distinguish between a crystallographic dimer and a non-crystallographic dimer based on these parameters, any references for this kind of analysis?

You can check the oligomeric status by other means such as size exclusion chromatography, native PAGE or NMR (although that one is among the difficult ones).

As Tomáš Hluska said, ideally you would confirm experimentally whether your protein forms oligomers in solution. There are various methods to do so.

For a review, see Chapter Methods to determine the oligomeric structure of proteins

Besides the methods mentioned by Tomáš, the combination of size exclusion chromatography and multi-angle light scattering yields good results Chapter Characterization of Protein Oligomers by Multi‐Angle Light Scattering

Computationally, ePISA will assess the probable quarternary structure and assign each interface in the crystal a probability of it being relevant in solution:

https://www.ebi.ac.uk/msd-srv/prot_int/pistart.html

"PDBePISA is an interactive tool for the exploration of macromolecular interfaces.

With PDBePISA, you can:

• Retrieve pre-calculated results for the whole PDB archive.
• Calculate results interactively for structures uploaded as PDB or mmCIF files These calculated results include:structural and chemical properties of macromolecular surfaces and interfaces probable quaternary structures (assemblies), their structural and chemical properties and probable dissociation pattern
• search the PDB archive for particular interfaces formed by structural homologs.
• search the PISA database of pre-calculated results using a wide range of options, such as:multimeric state, symmetry number, space group, accessible/buried surface area, free energy of dissociation, presence/absence of salt bridges and disulphide bonds, homomeric type, ligands keywords
• assess the significance (biological role) of macromolecular interfaces
• download and visualise structures, interfaces and assemblies using Rasmol (Unix/Linux platforms), Rastop (MS Windows machines) and Jmol (platform-independent server-side java viewer)"

Follow the "Publications" link for references, the "Tutorial" link for instructions on how to use the tool and interpret the results. It does not rely on a single measure to distinguish between crystal interfaces and interfaces relevant in solution, but a combination of many different parameters compared to statistics derived from the assessment of all structures in the PDB to derive the CSS score, a value between 0 and 1 that indicates whether a particular interface is crystallographic (low values) or an interface relevant in solution (high values). Read the tutorial for examples.