Ca+2-binding tyrosine phosphorylation-regulated protein (Ca+2-binding protein 86, testis-specific Ca+2-binding protein CBP86, fibrousheathin-2, FSP-2, CABYR, CBP86, FSP2)
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Function
- regulator of both motility- & head-associated functions including capacitation & the acrosome reaction in sperm
- isoform 1 binds Ca+2 in vitro
- isoforms 2 & 6 probably bind Ca+2
- isoforms 3 & 5 do not bind Ca+2 in vitro
- isoform 4 probably does not bind Ca+2
- isoform 3 self-associates
- isoforms 3 & 5 interact with GSK3B
- isoform 1 does not interact with GSK3B
- isoform 1 is phosphorylated on Tyr during in vitro capacitation
- isoforms 3 & 5 are phosphorylated by GSK3B in vitro
- dephosphorylation affects its ability to bind Ca+2
Structure
contains 1 RIIa domain
Compartment
- cytoplasm
- isoform 1, 3, 5: nucleus, cytoplasm
- localized to fibrous sheath including surface of longitudinal columns & ribs of the principal piece of sperm flagella
Alternative splicing
named isoforms=6
Expression
- expressed in elongating spermatids & spermatozoa
- isoform 1 is expressed in testis
- isoforms 3 & 5 are also expressed in brain, pancreas
Pathology
- isoforms 3 & 5 are also expressed in brain & numerous brain tumors