FSCB, a novel protein kinase A-phosphorylated calcium-binding protein, is a CABYR-binding partner involved in late steps of fibrous sheath biogenesis.
We report characterization of a novel testis- and sperm-specific protein, FSCB (fibrous sheath CABYR binding), that is expressed post-meiotically and localized in mouse sperm flagella. FSCB was identified as a binding partner of CABYR, a calcium-binding protein that is tyrosine-phosphorylated during capacitation. Orthologous genes of FSCB are present in other mammals, including rat and human, and conserved motifs in FSCB include PXXP, proline-rich and extensin-like regions. FSCB is phosphorylated by protein kinase A as shown by in vitro phosphorylation assay and also by determining phosphorylation sites in native FSCB from mouse sperm. Calcium overlay assay showed that FSCB is a calcium-binding protein from sperm. FSCB is a post meiotic protein first expressed at step 11 of mouse spermatogenesis in the elongating spermatids, and it subsequently incorporates into the flagellar principal piece of the sperm. Ultrastructurally, FSCB localized to a cortical layer of intermediate electron density at the surface of the ribs and longitudinal columns of the fibrous sheath. Due to its temporal appearance during spermiogenesis and location at the cortex of the fibrous sheath, FSCB is postulated to be involved in the later stages of fibrous sheath assembly.
Li
Yan-Feng
YF
Center for Research in Contraceptive and Reproductive Health, Department of Cell Biology, University of Virginia, Charlottesville, VA 22908, USA.
He
Wei
W
Jha
Kula N
KN
Klotz
Ken
K
Kim
Young-Hwan
YH
Mandal
Arabinda
A
Pulido
Silvia
S
Digilio
Laura
L
Flickinger
Charles J
CJ
Herr
John C
JC
D020816:Amino Acid Motifs / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D006801:Humans; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D013075:Sperm Capacitation / Q000502:physiology*; D013082:Sperm Tail / Q000378:metabolism* / Q000648:ultrastructure; D013087:Spermatids / Q000378:metabolism* / Q000648:ultrastructure; D013091:Spermatogenesis / Q000502:physiology*
C486726:Cabyr protein, mouse; D002135:Calcium-Binding Proteins; C525804:FSCB protein, mouse; D010750:Phosphoproteins; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium