Natalia Mast is the first author of a 2011 study explaining how the cholesterol side-chain cleavage enzyme carries out successive reactions converting cholesterol toward pregnenolone. The investigators studied the enzyme bound to the first oxygenated intermediate, combining a crystal structure with solution measurements.[ref]
The active site forms an elongated cavity leading toward the haem group. The intermediate's placement and interactions suggested that movement within this cavity permits successive reactions while the sterol remains associated with the enzyme. Solution spectroscopy tested changes in its position.[ref]
Structural basis for three-step sequential catalysis by the cholesterol side chain cleavage enzyme CYP11A1 by Natalia Mast and others. Abstract and Figure 3: structure and spectral comparisons
The example illustrates why one catalyst can support a multistep transformation without requiring the intermediate to diffuse freely after every step. A bound structure proposes spatial constraints; measurements in solution test whether the arrangement can change, rather than assuming that a crystal captures the only functional position.
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