Conformational scanning of individual EF-hand motifs of calcium sensor protein centrin-1

Centrin-1, a Ca2+ sensor protein of the centrin family is a crucial player for cell division in eukaryotes and plays a key role in the microtubule organising centre. Despite being regarded as a calcium sensor with a matched structure to calmodulin/troponin C, the protein undergoes mild changes in conformation and binds Ca2+ with moderate affinity. We present an in-depth analysis of the Ca2+ sensing by individual EFhand motifs of centrin-1 and address unsolved questions of the rationales for moderate affinity and conformational transitions of the protein. Employing the more sensitive approach of Trp scanning of individual EF-hand motif, we have undertaken an exhaustive investigation of Ca2+ binding to individual EF-hand motifs, named EF1 to EF4. All four EF-hand motifs of centrin-1 are structural as all of them bind both Ca2+ and Mg2+. EF1 and EF4 are the most flexible sites as they undergo drastic conformational changes following Ca2+ binding, whereas EF3 responds to Ca2+ minimally. On the other hand, EF2 moves towards the protein surface upon binding Ca2+. The independent filling mode of Ca2+ to EF-hand motifs and lack of intermotif communication explain the lack of cooperativity of binding, thus constraining centrin-1 to a moderate affinity binding protein. Thus, centrin-1 is distinct from other calcium sensors such as calmodulin. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

Centrin-1, a Ca2+ sensor protein, plays a crucial role in cell division and microtubule organizing center in eukaryotes. Through an in-depth analysis of individual EF-hand motifs, it is found that all four EF-hand motifs of centrin-1 bind both Ca2+ and Mg2+. The lack of intermotif communication and independent filling mode of Ca2+ explain the moderate affinity binding characteristic of centrin-1.