A Change in Domain Cooperativity Drives the Function of Calnuc.

Ravichandran Vignesh, Gopala Krishna Aradhyam

Biochemistry 2020 Jul 14

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With the increasing incidence of neurodegenerative disorders, there is an urgent need to understand the protein folding process. Examining the folding process of multidomain proteins remains a prime challenge, as their complex conformational dynamics make them highly susceptible to misfolding and/or aggregation. The presence of multiple domains in a protein can lead to interaction between the partially folded domains, thereby driving misfolding and/or aggregation. Calnuc is one such multidomain protein for which Ca2+ binding plays a pivotal role in governing its structural dynamics and stability and, presumably, in directing its interactions with other proteins. We demonstrate differential structural dynamics between the Ca2+-free and Ca2+-bound forms of calnuc. In the absence of Ca2+, full-length calnuc displays equilibrium structural transitions with four intermediate states, reporting a sum of the behavioral properties of its individual domains. Fragment-based studies illustrate the sequential events of structure adoption proceeding in the following order: EF domain followed by the NT and LZ domains in the apo state. On the other hand, Ca2+ binding increases domain cooperativity and enables the protein to fold as a single unit. Single-tryptophan mutant proteins, designed in a domain-dependent manner, confirm an increase in the number of interdomain interactions in the Ca2+-bound form as compared to the Ca2+-free state of the protein, thereby providing insight into its folding process. The attenuated domain crosstalk in apo-calnuc is likely to influence and regulate its physiologically important intermolecular interactions.

Citation

Ravichandran Vignesh, Gopala Krishna Aradhyam. A Change in Domain Cooperativity Drives the Function of Calnuc. Biochemistry. 2020 Jul 14;59(27):2507-2517