Shell coloration via mineral inclusions

[JackSullivan]

While a lot of the colored patterns found in shells such as the Cones can be attributed to the amino acid-derived pigments eumelanin and pheomelanin, the crystalline form of calcium carbonate that makes up most shell bodies can also be attributed to the inclusion of mineral ions during the enzymatic formation of the growing shell material.

Aragonite can range in color from colorless, white, brown, gray, yellow, red, pink, purple, orange, blue, & green by the inclusion of cations of the elements strontium, lead & zinc. Since shell coloration & color patterns are under genetic control, this raises the need for specialized proteins to act as transporters, capturing the specific metal cation from the sea water & transporting it to the growth zone to be deposited at the proper time in order to produce the desired color of the growing shell.

These 3 elements are all in the form of divalent (+2 charge) ions. They are found as their carbonates in the aragonite matrix.

Transport proteins are found across Nature. See

https://en.wikipedia.org/wiki/Transport_protein

To show how complex the biology of these transport proteins can be, here are 2 ribbon models of the ZntB zinc transporter protein. The model on the right shows the zinc cations as small gold balls. The ribbons are chains of amino acids.