Proteins Crystalize Minerals, Kill Bacteria

a brown softshell turtle lays on land, out of water with webbed feet lifted in the air

Biological Strategy

Chinese softshell turtle

AskNature Team

Image: J. Maughn / Flickr / CC BY NC - Creative Commons Attribution + Noncommercial

Protect From Microbes

In living systems, microbes play important roles, such as breaking down organic matter and maintaining personal and system health. But they also pose threats. Bacteria can be pathogens that cause diseases. Some bacteria create colonies called biofilms that can coat surfaces, reducing their effectiveness–for example, inhibiting a leaf’s ability to photosynthesize. Living systems must have strategies for protecting from microbes that cause disease or become so numerous that they create an imbalance in the system. At the same time, living systems must continue living in harmony with other microbes. Some living systems kill microbes. Others repel without killing to reduce the chances that microbes will adapt to the lethal strategy and become resistant to it. For example, some pea seedlings exude a chemical that inhibits biofilm buildup.

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Chemically Assemble Mineral Crystals

The vast majority of biochemical assembly and break down processes––even by the most complex organisms––occur within cells. In fact, cells are able to perform hundreds, even thousands, of chemical transformations at the same time under life-friendly conditions (ambient temperature and pressure in an aqueous environment). Within cells, organisms utilize organic compounds to facilitate the assembly of mineral crystals. For example, oysters utilize acidic proteins and sulfated polysaccharides to assemble layers of aragonite crystals.

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Reptiles

Class Reptilia (“creeping”): Lizards, crocodiles, turtles, snakes

Reptiles retain some of the key characteristics that first enabled vertebrates to live permanently on land. They have dry skin covered in scales made of keratin that help prevent water loss. (Amphibians still need to stick close to water to keep their skin moist.) Many reptiles reproduce by laying eggs that are watertight and have a yolk, so eggs can develop on land while staying moist and nourished. Reptiles are also ectotherms, meaning they don’t produce their own body heat. This means they burn through energy much more slowly than “warm blooded” creatures of the same size. It also means that they need to keep warm to keep active, which is why you might see them spending a seemingly inordinate amount of time simply basking in the sun.

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

Eggshell represents a barrier designed to protect against both mechanical forces and microbial infection. Researchers have recently discovered a , 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.

Last Updated August 23, 2016

References

Journal article

Structure, Self-Assembly, and Dual Role of a β-Defensin-like Peptide from the Chinese Soft-Shelled Turtle Eggshell Matrix

J. Am. Chem. Soc. | 15/03/2008 | 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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