15-million-year-old mollusk protein found

US scientists have discovered 'beautifully preserved' 15-million-year-old thin protein sheets in fossil shells of a snail-like mollusk.
Scientists from Carnegie Institution collected samples from Calvert Cliffs, along the shoreline of the Chesapeake Bay, a popular fossil collecting area in the US.
They found fossilised shells of a snail-like mollusk called Ecphora that lived in the mid-Miocene era - between 8 and 18 million years ago.
Ecphora is known for an unusual reddish-brown shell colour, making it one of the most distinctive North American mollusks of its era.
This colouration is preserved in fossilised remains, unlike the fossilised shells of many other fossilised mollusks from the Calvert Cliffs region, which have turned chalky white over the millions of years since they housed living creatures.

Shells are made from crystalline compounds of calcium carbonate interleaved with an organic matrix of proteins and sugars proteins and sugars.

These proteins are called shell-binding proteins by scientists, because they help hold the components of the shell together.
They also contain pigments, such as those responsible for the reddish-brown appearance of the Ecphora shell. These pigments can bind to proteins to form a pigment-protein complex.
The fact that the colouration of fossilised Ecphora shells is so well preserved suggested to the research team that shell proteins bound to these pigments in a complex might also be preserved.
They were surprised to find that the shells, once dissolved in dilute acid, released intact thin sheets of shell proteins more than a centimetre across.

Chemical analysis including spectroscopy and electron microscopy of these sheets revealed that they are indeed shell proteins that were preserved for up to 15 million years.
"These are some of the oldest and best-preserved examples of a protein ever observed in a fossil shell," said researcher Robert Hazen.
The proteins share characteristics with modern mollusk shell proteins. They both produce thin, flexible sheets of residue that's the same colour as the original shell after being dissolved in acid.
Of the 11 amino acids found in the resulting residue, aspartate and glutamate are prominent, which is typical of modern shell proteins.

Further study of these proteins could be used for genetic analysis to trace the evolution of mollusks through the ages, as well as potentially to learn about the ecology of the Chesapeake Bay during the era in which Ecphora thrived, researchers said.
The findings are published in the journal Geochemical Perspectives Letters.