P. Liang et al., MOLECULAR CHARACTERIZATION OF A SMALL HEAT-SHOCK ALPHA-CRYSTALLIN PROTEIN IN ENCYSTED ARTEMIA EMBRYOS, The Journal of biological chemistry, 272(30), 1997, pp. 19051-19058
Molecular chaperones protect cells during stress by limiting the denat
uration/aggregation of proteins and facilitating their renaturation. I
n this context, brine shrimp embryos can endure a wide variety of stre
ssful conditions, including temperature extremes, prolonged anoxia, an
d desiccation, thus encountering shortages of both energy (ATP) and wa
ter. How the embryos survive these stresses is the subject of continui
ng study, a situation true for other organisms facing similar physiolo
gical challenges. To approach this question we cloned and sequenced a
cDNA for p26, a molecular chaperone specific to oviparous Artemia embr
yos. p26 is the first representative of the small heat shock/alpha-cry
stallin family from crustaceans to be sequenced, and it possesses the
conserved alpha-crystallin domain characteristic of these proteins. Th
e secondary structure of this domain was predicted to consist predomin
antly of beta-pleated sheet, and it appeared to lack regions of alpha-
helix. Unique properties of the nonconserved amino terminus, which sho
wed weak similarity to nucleolins and fibrillarins, are enrichments in
both glycine and arginine. The carboxyl-terminal tail is the longest
yet reported for a small heat shock/alpha-crystallin protein, and it i
s hydrophilic, a common attribute of this region. Site-specific differ
ences between amino acids from p26 and other small heat shock/alpha-cr
ystallin proteins bring into question the functions proposed for some
of these residues. Probing of Southern blots disclosed a multi-gene fa
mily for p26, whereas two size classes of p26 mRNA at 0.7 add 1.9 kilo
base pairs were seen on Northern blots; the larger probably representi
ng nonprocessed transcripts, Examination of immunofluorescently staine
d samples with the confocal microscope revealed that a limited portion
of intracellular p26 is found in the nuclei of encysted embryos and t
hat it resides within discrete compartments of this organelle. The res
ults in this paper demonstrate clearly that p26 is a novel member of t
he small heat shock/alpha-crystallin family of proteins. These data, i
n concert with its restriction to embryos undergoing oviparous develop
ment, suggest that p26 functions as a molecular chaperone during expos
ure to stress, perhaps able; to limit protein degradation and thus ens
ure a ready supply of functional proteins when growth is reinitiated.