Scherffelia dubia centrin exhibits a specific mechanism for Ca(2+)-controlled target binding

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Centrins are conserved eukaryotic calcium-binding proteins.
• They belong to the EF-hand (or calmodulin) superfamily.
• Understanding algal centrins like Scherffelia dubia centrin (SdCen) is crucial for comparative biology.

Purpose of the Study:

• To investigate the molecular features and Ca(2+) binding properties of SdCen.
• To characterize the binding interactions of SdCen with natural target peptides.
• To elucidate the role of Ca(2+) in SdCen's molecular mechanisms and signaling.

Main Methods:

• Flow dialysis and isothermal titration calorimetry (ITC) were used to assess Ca(2+) binding.
• ITC was employed to quantify the binding of SdCen and its domains to target peptides.
• Analysis of centrin binding motifs (W(1)L(4)L(8)) and calmodulin binding motifs (W(1)F(5)V(8)F(14)) was performed.

Main Results:

• SdCen exhibits three Ca(2+) binding sites: two in the N-terminal domain and one in the C-terminal domain.
• Ca(2+) binding stabilizes the N-terminal domain, exposing a hydrophobic surface.
• SdCen binds target peptides via two sites: a high-affinity C-terminal site (constitutively bound) and a Ca(2+)-dependent low-affinity N-terminal site.

Conclusions:

• SdCen's Ca(2+) binding and metal ion-induced structural changes differ from human centrins but share similarities with CrCen.
• The C-terminal domain likely binds targets constitutively, while the N-terminal domain binds upon Ca(2+) signal.
• SdCen employs unique mechanisms to respond to cellular Ca(2+) signals, potentially applicable to other algal centrins.