EXPRESSION OF MULTIPLE ALPHA-1-ANTITRYPSIN-LIKE GENES IN HIBERNATING SPECIES OF THE SQUIRREL FAMILY

In the chipmunk, a mammalian hibernator, a 140 kDa protein complex fou nd in the blood, drastically decreases in concentration during hiberna tion. This complex contains four species of proteins, HP-20, -25, -27 and -55. In the present study, cDNA clones coding for the chipmunk HP- 55 were isolated from a liver cDNA library. Sequence analysis revealed that HP-55 is produced as a precursor protein of 413 amino acids (aa) , that it has a signal peptide of 24 aa, and that it contains four pot ential N-glycosylation sites. The deduced aa sequence shows 63% identi ty with that of rat alpha 1-antitrypsin (alpha 1-AT); however, the seq uence corresponding to the reactive center P1-P1' residues was found t o be Met-Leu, whereas it is Met-Ser in the rat alpha 1-AT. During scre ening of the chipmunk liver cDNA library, four other related classes o f cDNA clones were obtained, each also coding for an alpha 1-AT-like p rotein. In spite of more than 86% overall aa sequence identity among t he five chipmunk alpha 1-AT-like proteins, they are highly divergent i n the putative reactive center region; the putative P1-P1' sequences a re Met-Leu (HP-55 or CM55-ML), Met-Met (CM55-MM), Met-Ser (CM55-MS), S er-Ile (CM55-SI) and Ser-Thr (CM55-ST). Each of the alpha 1-AT-like pr otein mRNAs was expressed in chipmunk liver, and the HP-55 mRNA level was greatly reduced during hibernation. Genomic Southern blot analysis and screening of a liver cDNA library from another hibernating squirr el species, the ground squirrel, also revealed expression of multiple members of the alpha 1-AT gene family, whereas analysis of a cDNA libr ary from a non-hibernating species, the tree squirrel, found only a si ngle alpha 1-AT gene. (C) 1997 Elsevier Science B.V.