Biominerals and blood thinners: Insights into heparin's versatility and the role of water

What is it about?

Calcium ion (Ca2+) interactions with macromolecules regulate many biological functions, including the formation of biominerals (e.g., bones and shells) and blood anticoagulation. This study quantifies the strength of Ca2+ binding to three heparin family molecules and shows the binding is an entropy-dominated reaction through release of water molecules to increase disorder. Water rearrangement may also explain polysaccharide-specific controls on calcite (CaCO3) nucleation. Combining our data with published Ca2+ binding measurements indicates changes in water structuring also occur for many other biomacromolecules. However, polysaccharides and proteins present distinct relationships during interactions with Ca2+, suggesting a thermodynamic basis for how macromolecules can regulate cation activity in the low free energy reactions of biological systems.

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Photo by Neeqolah Creative Works on Unsplash

Photo by Neeqolah Creative Works on Unsplash

Why is it important?

Heparin is often used as a blood thinner after surgery or during kidney dialysis. Its global market size was estimated at $7.56 billion in 2023 and is expected to grow. Heparin is part of the heparan sulfate family of glycosaminoglycans, which are present in nearly all animal tissues. Heparan sulfates are just one of many different binding agents that use calcium to regulate a diverse portfolio of biochemical operations. The results of this paper provide a framework for understanding how heparan sulfates effectively broker a vast, diverse portfolio of operations — encompassing both biomineralization and biomedical applications.