CABYR, a novel calcium-binding tyrosine phosphorylation-regulated fibrous sheath protein involved in capacitation.
To reach fertilization competence, sperm undergo an incompletely understood series of morphological and molecular maturational processes, termed capacitation, involving, among other processes, protein tyrosine phosphorylation and increased intracellular calcium. Hyperactivated motility and an ability to undergo the acrosome reaction serve as physiological end points to assess successful capacitation. We report here that acidic (pI 4.0) 86-kDa isoforms of a novel, polymorphic, testis-specific protein, designated calcium-binding tyrosine phosphorylation-regulated protein (CABYR), were tyrosine phosphorylated during in vitro capacitation and bound (45)Ca on 2D gels. Acidic 86-kDa calcium-binding forms of CABYR increased during in vitro capacitation, and calcium binding to these acidic forms was abolished by dephosphorylation with alkaline phosphatase. Six variants of CABYR containing two coding regions (CR-A and CR-B) were cloned from human testis cDNA libraries, including five variants with alternative splice deletions. A motif homologous to the RII dimerization domain of PK-A was present in the N-terminus of CR-A in four CABYR variants. A single putative EF handlike motif was noted in CR-A at aas 197-209, while seven potential tyrosine phosphorylation-like sites were noted in CR-A and four in CR-B. Pro-X-X-Pro (PXXP) modules were identified in the N- and C-termini of CR-A and CR-B. CABYR localizes to the principal piece of the human sperm flagellum in association with the fibrous sheath and is the first demonstration of a sperm protein that gains calcium-binding capacity when phosphorylated during capacitation.
Naaby-Hansen
Soren
S
Ludwig Institute for Cancer Research, Royal Free and University College School of Medicine, London, W1P 8BT, United Kingdom.
Mandal
Arabinda
A
Wolkowicz
Michael J
MJ
Sen
Buer
B
Westbrook
V Anne
VA
Shetty
Jagathpala
J
Coonrod
Scott A
SA
Klotz
Kenneth L
KL
Kim
Young-Howan
YH
Bush
Leigh Ann
LA
Flickinger
Charles J
CJ
Herr
John C
JC
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D015180:Electrophoresis, Gel, Two-Dimensional; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D007106:Immune Sera; D008297:Male; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D010750:Phosphoproteins; D010766:Phosphorylation; D011110:Polymorphism, Genetic; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013075:Sperm Capacitation; D013094:Spermatozoa / Q000378:metabolism / Q000648:ultrastructure; D014443:Tyrosine / Q000378:metabolism
C448922:CABYR protein, human; D002135:Calcium-Binding Proteins; D018076:DNA, Complementary; D007106:Immune Sera; D010750:Phosphoproteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D014443:Tyrosine; D002118:Calcium