Characterization of a caltrin-like protein from human seminal plasma

ANAHÍ FRANCHI; ROSA MOLINA; CRISTINA MALDONADO; CARLOS E. CORONEL

Carlos Paz-Córdoba, Argentina

Congreso; XXXVIII Annual Meeting Argentina Society for Biochemistry and Molecular Biology; 2002

Sociedad Argentina de Bioquimica y Biologia Molcular

We previously reported the purification and aminoacid sequence of a 15 kDa caltrin-like (calcium transport inhibitor) protein from human seminal plasma (hSP) which was apparently bound to the head of ejaculated spermatozoa as observed in other species (XXXVI SAIB, 2000). To study the capability to interact with the sperm membrane and other functional properties of this protein, monospecific polyclonal antibodies were prepared in rabbits. Ejaculated sperm from different donors showed at least three fluorescence patterns when submitted to indirect immunofluorescence (IIF), indicating that the 15 kDa protein binds to the surface either: a) on the acrosomal region and the neck; b) on the whole head; and c) on acrosome, neck and tail. Similar distribution of the protein was visualized by immunocytochemistry and electron microscopy. To explore the type of interaction involved in the protein-sperm binding, washed ejaculated spermatozoa were extracted with 0.5 M KCl in Hepes-balanced salts, and the extract subjected to SDS-PAGE and western blotting. Although the differences in IIF pattern among samples, the presence of the 15 kDa protein in the western blots suggests that it was bound to the sperm membrane by electrostatic interactions. The meaning of different distribution of the 15 kDa protein on the sperm surface and its functional role are still unknown.