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C2 Domain
Class:Phospholipid Binding

No Image The C2 domain is composed of two, four stranded b-sheets creating three loops at the top of the domain and four at the bottom. Five conserved aspartate residues and one serine in upper loops 1 and 3 are involved in the binding of 3 calcium ions necessary for phospholipid binding. Analysis of the C2 domain from a number of different proteins reveals the C2 domains can exist in two topologies. In topology I (ie. C2A of synaptotagmin) the first b-strand occupies the same position as b-strand eight in topology II (ie. PLCd-1). The N and C terminus in topology I is oriented in the up position while in topology II the N and C terminus are oriented down. The functional significance of the two topologies remains unknown.

Structure Reference:
Sutton, RB. et al. (1998) Structure. 6(11):1395-405. PDB: 1A25.

 structure bis

Domain binding and function:
The C2 domain is a region containing approximately 130 residues involved in binding phospholipids in a calcium dependent manner or calcium independent manner. C2 domains are found in over 100 different proteins with functions ranging from signal transduction to vesicular trafficking. Calcium binding to the C2 domain of synaptotagmin induces little conformational change in the C2 domain but rather calcium induces a change in the electrostatic potential enhancing phospholipid binding, suggesting the C2 domain functions as an electrostatic switch. In addition to electrostatic interactions, side chains in the calcium binding loops influence the binding of different C2 domains to either neutral or negatively charged phospholipids.
Examples of Proteins: 
C2 domain protein
Binding partner
PKC b Ser/Thr Kinase Ca2+ and acidic phospholipids
Synaptotagmin Integral membrane protein in synaptic vesicles Ca2+ and acidic phospholipids

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