Crystal clear: using neutrons to tackle a fundamental biotechnological challenge

ILL's instruments play a crucial role in disentangling complex protein crystallisation pathways.

The crystallisation of proteins is a double-edged sword. If it occurs in an uncontrolled manner in pharmaceutical formulations or in the human body, it can compromise the efficacy of the formulation or cause severe disease, respectively. At the same time, getting proteins to crystallise in vitro is an essential prerequisite for the elucidation of protein structures - and a difficult one, too. Crystallisation assays are often a tedious undertaking relying on trial and error and systematic, simplified approaches are difficult to establish.

One possibility to induce crystallisation in a controlled manner is to add certain substances to protein solutions. A case in point are polymers and charged molecules or atoms. In particular, multivalent salt ions (carrying more than one electric charge) have been shown to be efficient promoters of protein crystallisation.

A team of ILL researchers and their collaborators from Tübingen (Germany) and Lund (Sweden) used a multimethod approach to obtain detailed insights into the pathways underlying the crystallisation of the protein human serum albumin (HSA) in the presence of the multivalent ion La³⁺. "Already in the first assays using optical microscopy and small-angle neutron scattering (SANS), we were excited to see that even tiny differences in La³⁺ concentration drastically altered the crystal structure we obtained", says Christian Beck, the first author of the team's newest publication. "This motivated us to perform further experiments on this intriguingly sensitive system."

The team went on to characterise their HSA-La³⁺ samples in real-time, starting from isolated protein molecules in solution up to large crystalline assemblies. To this end, the researchers exploited a large variety of the ILL's instrument suite.