In midwinter, temperatures at the home of an Alaskan darkling beetle (Upis ceramboides) can drop to -76 degrees F (-60 degrees C), yet this beetle species is able to keep its internal, watery cell contents from catastrophically freezing. Unlike most other extreme cold-dwelling organisms, including plants, animals, fish, fungi, and bacteria that use proteins as antifreeze agents, this Alaskan beetle produces a sugar-based antifreeze called xylomannan (a polymer of alternating xylose and mannose sugars). With the help of certain oily compounds, xylomannan attaches to the outer cell membrane where it likely functions to prevent the entry of extracellular ice into the cell, keep ice from forming inside the cell, and promote membrane stability.
“In the most northern climates, like the interior of Alaska, midwinter temperatures fall as low as minus 60 degrees Fahrenheit, and snow cover and subzero temperatures can last until May. At these extreme temperatures, most insects are bugsicles. The Alaskan Upis beetle, for example, freezes at around minus 19 degrees. But, remarkably, it can survive exposure to temperatures as low as about minus 100 degrees…a new kind of antifreeze was recently discovered in the Upis beetle by a team of researchers from the University of Notre Dame and the University of Alaska-Fairbanks. Unlike the protein antifreezes of other beetles, snow fleas and moths, the Upis antifreeze is a complex sugar called xylomannan that is as effective at suppressing ice growth as the most active insect protein antifreezes” (Carroll 2010).
When Built-In Antifreeze Beats a Winter Coat
“Although all previously described TH [Thermal hysteresis]-producing biomolecules are proteins, most thermal hysteresis factors (THFs) have not yet been structurally characterized…We isolated a highly active THF from the freeze-tolerant beetle, Upis ceramboides…the THF contained little or no protein, yet it produced 3.7 ± 0.3 °C of TH at 5 mg/ml, comparable to that of the most active insect antifreeze proteins…this antifreeze contains a β-mannopyranosyl-(1->4) β-xylopyranose backbone and a fatty acid component, although the lipid may not be covalently linked to the saccharide…This xylomannan is the first TH-producing antifreeze isolated from a freeze-tolerant animal and the first in a new class of highly active THFs that contain little or no protein…We investigated…U. ceramboides, from interior Alaska because they tolerate freezing to -60 °C in midwinter.” (Walters et al. 2009:20210).
“…The fatty acid component may anchor the THF to the cell membrane. However, the mode of lipid linkage to the saccharide has not been established, and it remains possible that the lipid is not covalently linked to the saccharide constituent.” (Walters et al. 2009:20211).
“The observation that THFs were associated with the cell membrane in the [a] centipede, as also appears to be the case for THFs from U. ceramboides, suggests that these molecules may prevent the spread of extracellular ice into the cytosol (intracellular freezing is typically thought to be lethal) and/or stabilize the plasma membrane at low temperature. This study shows that a (lipo)xylomannan isolated from U. ceramboides is a highly active THF that is structurally distinct from all known AFPs and antifreeze glycoprotein (AFGPs) reported to date. In contrast to known AFGPs, which comprise ~39% peptide by mass, THFs isolated from U. ceramboides contain little to no protein. In addition, the β-Manp-(1->4) β-Xylp backbone is unrelated to the saccharide component of fish AFGPs…This xylomannan antifreeze may contribute to freeze tolerance by preventing recrystallization of extracellular ice, preventing intracellular freezing and/or stabilizing cellular membranes at low temperature.” (Walters et al. 2009:20214).