EF-hand, extracellular calcium-binding (EC) motif, found in testican-2 (TICN2)
TICN2, also termed SPARC/osteonectin, CWCV, and Kazal-like domains proteoglycan 2 (Spock2), is an extracellular heparan sulphate proteoglycan expressed in brain, lung, and testis. It inhibits neurite extension from cultured primary cerebellar neurons and may play regulatory roles in the development of the central nervous system. It also participates in diverse steps of neurogenesis. Moreover, TICN2 may contribute to ECM remodeling by regulating function(s) of other testican family members, which possess membrane-type matrix metalloproteinases (MT-MMPs) inhibitory function. Furthermore, TICN2 corresponding gene SPOCK2 acts as a susceptibility gene for bronchopulmonary dysplasia. TICN2 contains an N-terminal signal peptide, a testican-specific domain followed by a follistatin-like (FS) domain, an extracellular calcium-binding (EC) domain including a pair of EF hands, a thyroglobulin-like domain (TY), and a C-terminal region with two putative glycosaminoglycan attachment sites. The substitution of a ligating Asp residue by Tyr292 in the +Y position of EF-hand 2 in TICN2 could prevent Ca2+ binding to this site and also cause EF-hand 1 to bind one Ca2+ ion with low affinity.
Feature 1:putative Ca binding site [ion binding site]
Evidence:
Comment:Based on the structure evidence how the first EF-hand motif in Homo sapiens SPARC (1SRA) binds Ca2+ ion.
Comment:Unlike other members in SPARC family, the substitution of a ligating Asp residue by Tyr292 in the +Y position of EF hand 2 in testican-2 could prevent Ca2+ binding to this site and also cause EF-hand 1 to bind one Ca2+ with low affinity.
Jiyao W et al.(2023). "The conserved domain database in 2023.",