Alterations in the properties of sperm protamine-like II protein after exposure of Mytilus galloprovincialis (Lamarck 1819) to sub-toxic doses of cadmium

Abstract

Protamine-like proteins (PL-II, PL-III and PL-IV) represent the major basic nuclear component of Mytilus galloprovincialis L sperm chromatin. The present study investigates the effects induced on the properties of PL-II protein after exposure of Mytilus galloprovincialis L for 24 h to 1.5 and 5 µM CdCl₂. We found cadmium accumulation in protamine-like proteins with a linear grow up with the exposition dose. In particular, after 5 µM CdCl₂ mussels exposure, the mobility of PL-II band changed in SDS-PAGE, suggesting structural rearrangement in presence of cadmium. Structural analysis using fluorescent probes, indicated that at 5 µM CdCl₂ the complete conformational change of PL-II protein was reached. In the same condition of mussels exposure of 5 µM CdCl₂, PL-II protein changed its DNA binding mode, which determined a closer DNA binding, because higher amount of NaCl were required for PL-II protein release by sperm nuclei. These results supported the hypothesis that mussel exposure to this CdCl₂ dose, although lower to toxic ones, affects the properties of this protein and as a consequence chromatin organization of spermatozoa that is essential for the success of fertilization.

Keywords: Cadmium; Metal bioaccumulation; Metal pollution; Mytilus galloprovincialis L.; Protamine-like proteins; Sperm chromatin.