The crystal structure of Arabidopsis BON1 provides insights into the copine protein family

Abstract

SUMMARY The Arabidopsis thaliana BON1 gene product is a member of the evolutionary conserved eukaryotic calcium‐dependent membrane‐binding protein family. The copine protein is composed of two C2 domains (C2A and C2B) followed by a vWA domain. The BON1 protein is localized on the plasma membrane, and is known to suppress the expression of immune receptor genes and to positively regulate stomatal closure. The first structure of this protein family has been determined to 2.5‐Å resolution and shows the structural features of the three conserved domains C2A, C2B and vWA. The structure reveals the third Ca2+‐binding region in C2A domain is longer than classical C2 domains and a novel Ca2+ binding site in the vWA domain. The structure of BON1 bound to Mn2+ is also presented. The binding of the C2 domains to phospholipid (PSF) has been modeled and provides an insight into the lipid‐binding mechanism of the copine proteins. Furthermore, the selectivity of the separate C2A and C2B domains and intact BON1 to bind to different phospholipids has been investigated, and we demonstrated that BON1 could mediate aggregation of liposomes in response to Ca2+. These studies have formed the basis of further investigations into the important role that the copine proteins play in vivo.

BONZAI Proteins Control Global Osmotic Stress Responses in Plants

“…The BON1 protein binds to Ca 2+ through its N-terminal C2 domains, and this binding property is essential for its function [30]. A recent structural study finds additional Ca 2+ binding site in its C-terminal region and Ca 2+ binding alters its conformation [53]. These results indicate that BON1 is a Ca 2+ -responsive protein, and therefore may contribute to Ca 2+ homeostasis in response to an initial Ca 2+ elevation.…”

How plants sense and respond to osmotic stress

“…BON/Copine proteins consist of two Ca 2+ ‐dependent phospholipid‐binding C2 domains, which are unique among peripheral membrane proteins and reversibly attached to phospholipids by forming a Ca 2+ bridge between the acidic residues located on Ca 2+ ‐binding regions and phosphate groups of lipids (Wang et al, 2020). Similar to human copines, BON1 binds to negatively charged phospholipids, including phosphatidylglycerol (PG), PS, and phosphatidylinositol (PI), in a Ca 2+ ‐dependent manner in vitro (Creutz et al, 1998; Hua et al, 2001; Wang et al, 2020). The Ca 2+ binding ability of C2 domains determines BON1 function and probably BON1 partitioning on the plasma membrane; while the N‐terminal glycine 2 residue myristoylation is required for its plasma membrane localization and function (Li et al, 2010).…”

“…BON function together with the plasma membrane autoinhibited Ca 2+ ‐ATPase8 (ACA8) and ACA10 in mediating Ca 2+ signals, which are also critical for multiple cell‐surface signaling and physiological responses (George et al, 2008; Yang et al, 2017; Li et al, 2018; Yu et al, 2018). BON/Copine proteins consist of two Ca 2+ ‐dependent phospholipid‐binding C2 domains, which are unique among peripheral membrane proteins and reversibly attached to phospholipids by forming a Ca 2+ bridge between the acidic residues located on Ca 2+ ‐binding regions and phosphate groups of lipids (Wang et al, 2020). Similar to human copines, BON1 binds to negatively charged phospholipids, including phosphatidylglycerol (PG), PS, and phosphatidylinositol (PI), in a Ca 2+ ‐dependent manner in vitro (Creutz et al, 1998; Hua et al, 2001; Wang et al, 2020).…”

Copines, a Family of Calcium Sensor Proteins and Their Role in Brain Function

“…Until recently, the lack of 3D structural information resulted in partial misidentification of Copine domain borders in several biochemical and functional studies, particularly affecting C2 domain boundaries. To date, a 3D structure was determined experimentally only for plant Copine protein BON1 [ 29 ]. The arrival of powerful AI-based structure prediction algorithms [ 30 ] extended 3D structural information to other members of the Copine family ( Table 1 ).…”