The eggshells of the Chinese softshell turtles are both strong and antimicrobial due to the production of a single protein, pelovaterin.

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Eggshell represents a barrier designed to protect against both mechanical forces and microbial infection. Researchers have recently discovered a protein, pelovaterin, that is responsible for both roles. It forms spherical aggregates which trigger the formation of mineral crystals for deposition of the egg shell scaffold. Pelovaterin is also effective at killing certain strains of pathogenic bacteria by an as-of-yet unknown membrane active mechanism. The dual activity of pelovaterin means that turtles can synthesize one protein that both creates eggshell and protects it from infection if it cracks.

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"Biomineral matrix formation and molecular recognition are two important processes associated with eggshell biomineralization. To understand these two processes, a major intracrystalline peptide, pelovaterin, was isolated from turtle (Pelodiscus sinensis) eggshell and its tertiary and quaternary structures were established. The global fold of pelovaterin is similar to that of human β-defensins...Pelovaterin exhibits strong antimicrobial activity against two pathogenic Gram-negative bacteria, Pseudomonas aeruginosa and Proteus vulgaris...The results demonstrate the adaptability of an extracellular matrix protein to perform multiple tasks: polymorph discrimination and protection of the contents of the egg against bacterial invasion." (Lakshminarayanan et al. 2008: 4660)

"The 3D structure of pelovaterin exhibits significant similarity with cationic antimicrobial peptides derived from mammals, known as defensins." (Lakshminarayanan 2008: 4662)

"Eggshell is a sophisticated chemical defense against mechanical stress and microbial invasion for embryonic development. Any form of defect or damage of the shell causes microbial infection, results in embryonic mortality, and has important economic implications for the poultry industry. The matrix proteins are distributed throughout the eggshells in small amounts and they could act as excellent chemical defenses against microbes." (Lakshminarayanan et al. 2008: 4666)

"[T]he micellar assembly of pelovaterin provides a number of nucleating sites...Mineral particles continue to grow from each nucleating site until they collide with the neighboring particles resulting in the precipitation of spherical particles that coarsened (due to the presence of rigid template) to form a mineral film." (Lakshminarayanan et al. 2008: 4668)

Journal article
Structure, Self-Assembly, and Dual Role of a β-Defensin-like Peptide from the Chinese Soft-Shelled Turtle Eggshell MatrixJ. Am. Chem. Soc.March 15, 2008
Rajamani Lakshminarayanan, Subramanian Vivekanandan, Ramar Perumal Samy, Yajnavalka Banerjee, Emma Ooi Chi-Jin, Kay Wah Teo, Seetharama D. S. Jois, R. Manjunatha Kini, Suresh Valiyaveettil

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Chinese Softshell TurtlePelodiscus sinensisSpecies

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