cDNA cloning and expression of grp94 in the Pacific oyster Crassostrea gigas

The 94-kDa glucose-regulated protein (GRP94) is an endoplasmic reticulum (ER) chaperone. We cloned the first mollusk grp94 from a cDNA library of the Pacific oyster Crassostrea gigas. Analysis of C. gigas grp94 (cggrp94) clone containing 3212 bp DNA revealed that the cDNA contains a 2391 bp open reading frame that encodes a 797 amino acid protein of 91.6 kDa. The deduced amino acid sequence of cgGRP94 is 67%, 68%, and 67% homologous to the GRP94 of Homo sapiens, GP96 of Strongylocentrotus purpuratus, and GP96 of Xenopus laevis, respectively. CgGRP94 contains an N-terminal 22 amino acid sequence, which is characteristic of a signal sequence. It also contains a HATPase_c domain. In addition, it contains the KDEL (-Lys-Asp-Glu-Leu) peptide motif at the C-terminus, which suggests that cgGRP94 localizes in the ER. Northern blot analysis showed that cggrp94 mRNA is expressed at high levels in the gill which cggrp94 mRNA is induced during air exposure condition. Expression patterns of cggrp94 mRNA differed between gill and mantle, and cggrp94 mRNA was induced at high temperature during air exposure condition. These indicate that cggrp94 mRNA is induced by hypoxia and heat shock stress, and there are different strategies for air exposure condition between gill and mantle.