What medicine can learn from squid teeth

Many types of squid have razor-sharp teeth. They just are not where you’d expect to find them. Each of the suckers that run along a squid’s tentacles hides a ring of teeth. Those teeth prevent the animal’s prey from swimming away. They also are more than just a curiosity. Scientists want to create squid-inspired materials that will be just as strong as these barbs. Data from a new study may help them do that.

Before they could start designing the new materials, scientists had to understand what makes squid teeth so strong. Some have launched such work by focusing on the large molecules — suckerin proteins — that make up the teeth.

Akshita Kumar is a graduate student at Nanyang Technological University in Singapore. Along with researchers at A*STAR’s Bioinformatics Institute, also in Singapore, her group has identified dozens of suckerin proteins. They form strong, stretchy structures, called beta-sheets, Kumar’s team reports. (These structures also make spider silk strong and stretchy.) The new data show that these squid proteins are thermoplastic. That means they melt when heated and then turn solid again when cooled.

“This makes the material moldable and re-usable,” Kumar explains. She presented her team’s findings in late February at a conference of the Biophysical Society in Los Angeles, Calif.

With help from bacteria

Kumar’s studies have focused on suckerin-19, one of the most common of these proteins. She works in the lab of materials scientist Ali Miserez, who has been studying the squid proteins since 2009.

Kumar doesn’t need to remove a squid’s teeth to study the proteins. Instead, scientists in Miserez’s lab can “train” bacteria to make the proteins. To do this, the researchers change genes in the single-celled microbes. In this way, the team can get plenty of suckerin proteins — even when there are no squid around.

Scientists used to believe a squid’s sucker teeth were made from a hard material called chitin (KY-tin). “Even textbooks sometimes mention they’re made from chitin,” notes Kumar. But that’s not true, her team has now shown. The teeth also are not made from minerals like calcium, which give human teeth their strength. Instead, the squid’s ring teeth contain proteins and only proteins. That’s exciting, says Kumar. It means that a super-strong material can be made using just proteins — no other minerals required.

And unlike silks (such as those proteins made by spiders or cocoon-making insects), the squid stuff forms under water. That means squid-inspired materials might be useful in wet places, such as inside the human body.

Materials scientist Melik Demirel works at Pennsylvania State University in University Park. There he works on squid proteins and knows about research in this field. The Singapore group is “doing interesting stuff,” he says. At one time in the past, he collaborated with the Singapore team. Now, he says, “we’re competing.”

Collaboration and competition have driven the field forward, he notes. Only in the last few years have scientists begun to really understand the structure of the proteins in squid teeth. He hopes to put that knowledge to good use.

Recently, Demirel’s lab produced a squid-inspired material that can heal itself when it gets damaged. The Singapore group focuses on understanding what nature has produced in the teeth. Demirel says his team is trying to make things “beyond what nature has provided.”

Power Words

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bacterium    (pl. bacteria) A single-celled organism. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.

calcium    A chemical element which is common in minerals of the Earth’s crust and in sea salt. It is also found in bone mineral and teeth, and can play a role in the movement of certain substances into and out of cells.

graduate student     Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).

materials science     The study of how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application.

mineral     The crystal-forming substances, such as quartz, apatite, or various carbonates, that make up rock. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in certain regular three-dimensional patterns). (in physiology) The same chemicals that are needed by the body to make and feed tissues to maintain health.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O₂), but water is made of two hydrogen atoms and one oxygen atom (H₂O).

prey     (n.) Animal species eaten by others. (v.) To attack and eat another species.

proteins     Compounds made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. The hemoglobin in blood and the antibodies that attempt to fight infections are among the better-known, stand-alone proteins. Medicines frequently work by latching onto proteins.

silk     A fine, strong, soft fiber spun by a range of animals, such as silkworms and many other caterpillars, weaver ants, caddis flies and — the real artists — spiders.

Singapore    An island nation located just off the tip of Malaysia in southeast Asia. Formerly an English colony, it became an independent nation in 1965. Its roughly 55 islands (the largest is Singapore) comprise some 687 square kilometers (265 square miles) of land, and are home to more than 5.6 million people.

squid     A member of the cephalopod family (which also contains octopuses and cuttlefish). These predatory animals, which are not fish, contain eight arms, no bones, two tentacles that catch food and a defined head. The animal breathes through gills. It swims by expelling jets of water from beneath its head and then waving finlike tissue that is part of its mantle, a muscular organ. Like an octopus, it may mask its presence by releasing a cloud of “ink.”

sucker     (in botany) A shoot from the base of a plant. (in zoology) A structure on the tentacles of some cephalopods, such as squid, octopuses and cuttlefish.

suckerins         A family of structural proteins that form the basis of many natural substances, from spider silk to the teeth on a squid’s suckers.

thermoplastic      A term for substances that become plastic — able to transform in shape — when heated, then hardened when cooled. And these reshaping changes can be repeated over and over.