Towards the energy landscape of adenylate kinase in crowded milieu: Activity, conformation, structure and dynamics in sequence.

Enzyme function is governed by a complex network of conformational changes and internal dynamics, with the same getting more convoluted in the crowded cellular environment. Here, we have explored an intricate interplay amongst activity, structure, conformation, and dynamics of a multidomain enzyme, AK3L1 (UniProtKB: Q9UIJ7) in the crowded milieu. We have monitored changes in the enzyme landscape in response to the chemical denaturant, urea, under the influence of different concentrations of macromolecular crowders. Extensive experimental analyses using FRET-based domain displacement measurements, sub-nanosecond time scale local dynamics, and global structural changes, along with enzymatic activity studies, have been carried out to get deeper insights into the factors that may modulate the functional landscape of adenylate kinase (AK3L1). It was observed that AK3L1 gets activated at low urea concentrations, whereas higher urea concentrations unfold and thereby deactivate the enzyme. A sequential response of AK3L1 is observed towards external perturbation (urea) occurring through a series of well-defined steps. Incorporation of crowders not only shift the maximum activity of enzyme to a higher urea concentration, but also enhance domain compaction, as revealed by FRET studies. The modulation in enzyme activity and solvation dynamics acting as local response, precede global unfolding of the enzyme, indicating that the structural alterations around the active site are quite decoupled from the large amplitude global transitions.

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