Molecular cloning of cDNA encoding a bovine selenoprotein P-like protein containing 12 selenocysteines and a (His-Pro) rich domain insertion, and its regional expression

Abstract

When cDNA containing proteins enriched in the bovine cerebellar cortex were cloned, a clone which seemed to encode a selenoprotein P-like protein was isolated. The coding nucleotide sequence of its cDNA insert displayed high homology to rat and human selenoprotein P cDNA but contained 12 rather than 10 TGAs (12 rather than 10 selenocysteines in deduced amino acids), a tandem repeat of one CACTCC (His-Ser) and seven CATCCCs (His-Pro), and a 3' untranslated region approximately 890 bases shorter than that of rat liver selenoprotein P. RT-PCR using a set of primers flanking to the repeat displayed the existence of mRNA without the repeat. The tandem repeat and its adjacent region consisted of a similar motif of CAC/TCC/AC/T. Thus, these proteins included a (His-Pro) rich domain with a slightly negative free energy change irrespective of having the tandem repeat or not. Such His-Pro repeats reportedly exist in the segmentation gene paired or homeobox protein Om(1D) of Drosophila. Moreover, both this selenoprotein P-like protein mRNA and selenoprotein P mRNA were expressed in all the areas of the brain but most prominently in the cerebellar cortex, hippocampus, and olfactory bulb. These findings suggest the possibility that these selenoproteins are major selenium carriers in the brain and play a role in the morphological response of nerve or glial cells.