Variation in the ribosome interacting loop of the Sec61[alpha] from Giardia lamblia

The interaction between the ribosome and the endoplasmic reticulum-located Sec61 protein translocon is mediated through an arginine residue of Sec61[alpha], which is conserved in all prokaryotic and eukaryotic orthologues characterized to date. Using in silico approaches we report that instead of arginine, this ribosome-interaction function is most likely discharged by a lysine residue in the protist Giardia lamblia. This functional substitution of the R with a K in GlSec61[alpha] may have taken place to accommodate a G-rich rRNA.