In sperm chromatin, highly basic, positively charged proteins called protamine are used to condense DNA tightly to a final volume roughly 1/20th that of a somatic nucleus. Zinc is present in high concentrations in the seminal fluid and has been shown to play an important role in many sperm functions including sperm chromatin stability, sperm motility, and capacitation. Here, we aim to systematically investigate the role of zinc, and other divalent cations, on the DNA packaging inside sperm nuclei. Divalent cations, such as Zn, are known to effectively screen electrostatic interactions but typically are not able to induce DNA condensation on their own. Counterions having a net charge of +3 or higher are required to overcome the inherently large repulsion between DNA helices and mediate DNA condensation. Using small-angle X-ray scattering (SAXS), we observe that the addition of low concentrations of zinc to isolated salmon sperm nuclei results in tighter DNA packaging. This enhanced DNA packaging is also observed in salmon sperm nuclei with other divalent cations including transition metals, alkaline earth metals, and alkylamines. Experiments with reconstituted protamine/DNA also show the presence of divalents like zinc enhances <i>in vitro</i> condensation through a cooperative attractive interaction. At higher divalent concentrations, we observe a crossover behavior resulting in lower DNA packaging density at high salt concentrations. Lastly, we use ICP-MS to quantify the naturally occurring concentrations of Zinc and other metals in salmon sperm nuclei. Our measurements indicate the use of both protamine and divalent metals may be essential for optimized stabilization of the DNA in sperm chromatin.

Elucidating the role of zinc in salmon sperm nuclear DNA packaging

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.