Functional properties of caltrin proteins from seminal vesicle of the guinea pig

Abstract

Caltrin proteins from seminal vesicle content of the guinea pig bind with great specificity to different regions of the spermatozoa. Indirect immunofluorescence studies with polyclonal antibodies showed that caltrin I binds to the head, on the acrosomal cup, while caltrin II binds on the principal tail and the neck. No fluorescence was detected either in the midpiece or in the post-acrosomal area of the head when sperm were exposed to either of the caltrins. Calcium-induced hyaluronidase release, which occurs during the acrosomal reaction, was dramatically inhibited by caltrin I (approximately 85% inhibition). Caltrin II was less effective in preventing the enzyme release (approximately 50% inhibition). Chemical modification of the structure modified the biological activity of the two caltrins. Reduction and carboxymethylation of the cysteine residues diminished the inhibitory activity on 45Ca2+ uptake and reduced the ability of the proteins to react with their antibodies. Removal of the carbohydrate portion by chemical deglycosylation transformed the inhibitor proteins into enhancers of calcium uptake into the spermatozoa. Caltrin proteins from the guinea pig appear to play the same physiological role as bovine caltrin, regulating specifically calcium transport across the spermatozoal membranes related with the acrosome reaction and hyperactivation process. The dual behavior of caltrins to inhibit or enhance Ca2+ uptake enables them to fulfill this function. Nevertheless, molecular mechanisms different from those described for bovine caltrin seem to be involved in the control of the functional activity of the guinea pig caltrins.

Molecular characterization of epididymal proteins

“…Closely related proteins have been cloned from epididymal tissue of other species (Ellerbrock et al, 1994;Xu et al, 1996). The positions of half-cysteines suggested that they are twodomain members of the 'four-disulfide core'-or 'whey acidic' protein (WAP)-domain proteins, to which the human seminal plasma proteinase inhibitor, HUSI-I/SLPI (Seemüller et al, 1986;Jin et al, 1997), and a decapacitation factor of guinea-pig spermatozoa, caltrin II, belong (Coronel and Lardy, 1992). HE4 antipeptide antisera react with an antigen of the epididymal epithelium and duct lumen (Fig.…”

Electron Microscopic Immunolocalization of Caltrin Proteins in Guinea Pig Seminal Vesicles

“…They are small (M, = 5082 and 6255), basic (PIS 9.5 and 10.2) molecules that contain cysteines and carbohydrates in their structures [6]. Both caltrins inhibit with almost the same intensity the uptake of extracellular Ca2+ by capacitated epididymal spermatozoa [5].…”

“…They are small (M, = 5082 and 6255), basic (PIS 9.5 and 10.2) molecules that contain cysteines and carbohydrates in their structures [6]. Both caltrins inhibit with almost the same intensity the uptake of extracellular Ca2+ by capacitated epididymal spermatozoa [5]. However, each caltrin interacts specifically with different zones of the spermatozoa and affects the development of Ca-dependent physiologic processes localized in those areas and involved in fertilization.…”

“…However, each caltrin interacts specifically with different zones of the spermatozoa and affects the development of Ca-dependent physiologic processes localized in those areas and involved in fertilization. Thus, caltrin I binds to the head of the spermatozoa on the acrosomal area and inhibits the onset of the acrosome reaction; caltrin I1 interacts with principal tail of the spermatozoa and prevents the development of hyperactivation [5].…”

“…Reduction and carboxymethylation of the sulfhydryl groups abolish the inhibitory effect of the two proteins, while removal of the sugar moiety transformed them into enhancers of calcium transport [5]. The dual behavior of caltrins to inhibit or enhance Ca2+ uptake enables them to regulate the fertilization process through the control of the Ca2+ movement across the spermatozoa1 membranes.…”