Identification of novel blood proteins specific for mammalian hibernation

Mammalian hibernation is a unique physiological adaptation that allows the sustainment of life under extremely low body temperatures. In the chipmunk, we found four proteins related specifically to hibernation. These proteins started to diminish in concentration in the blood before and disappeared during hibernation. These proteins reappeared in the blood as hibernation ceased and remained during nonhibernation. The complete or partial amino acid sequences of the four proteins showed that three (27-, 25-, and 20-kDa) were previously unknown, whereas another (55-kDa) is highly homologous with alpha 1-antitrypsin. The three novel proteins are homologous, indicating that they are a family. In the NH2-terminal regions of these proteins, a collagen-like amino acid sequence is present, whereas in their COOH-terminal regions, two sequences, Ser-Ala-Phe-Ala-Val-Lys and Val-Trp-Leu-Glu, are conserved. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions and gel permeation chromatography under denaturating conditions revealed that the four proteins form a 140-kDa complex in the plasma fraction. The novel proteins were detected in blood of another hibernator, the ground squirrel, but not in rodent nonhibernators, namely tree squirrels and rats. The present finding is the first identification of a hibernation-specific protein. The presence of specific proteins in hibernators suggests the involvement of genetic factors in the control of hibernation. These proteins provide valuable tools for understanding molecular mechanisms of mammalian hibernation.