Two rodent suborders have evolved missing amino acids in the lipid-binding region of apolipoprotein E.

The order Rodentia comprises nearly 45% of all extant taxa, currently organized into 31 living families, some 450 genera, and roughly 2010 species (Kelt & Patton, 2020). Considering that rodents began evolving at least 66 million years ago, it is not surprising that they have diversified into five distinct suborders. With the advent of molecular biology, this difference can often be seen at the molecular level as well. Previous studies have indicated that the apolipoprotein E (APOE) of guinea pigs, belonging to the suborder Hystricomorpha, have fewer amino acids than have been reported for other suborders of Rodentia. Searching the genomic database for hystricomorph APOE genes, it was found that hystricomorphs were missing residues both in the vicinity of the hinge region and in the lipid-binding region of the apolipoprotein. In the hinge region, missing residues varied between 5 and 3, and in the latter region, seven residues were missing. The search also revealed that castorimorphs, although lacking the smaller of the two deletions, were also missing the same seven residue deletion as found in APOE of the hystricomorphs.