Homologs of the chaperones GroEL and DnaK are the most abundant proteins in <i>Hodgkinia</i>.

The exponentially modified protein abundance index (emPAI) is a rough measure of relative protein amounts in complex mixtures, derived from the number of sequenced peptides and normalized by the expected number per protein [58]. All proteins from Hodgkinia with at least 2 unique peptides are ranked by their emPAI values. Based on homology of the 15 proteins identified in Hodgkinia, 60% (9/15) were involved in amino acid synthesis, 20% (3/15) could not be assigned to a general metabolic function, 13% (2/15) were involved in protein folding and stability, and 7% (1/15) were involved in translation. These results are not a complete listing of all expressed proteins, as exhaustive coverage of the symbiont proteome is difficult because the bacteria cannot be grown in pure culture, resulting in massive contamination from insect proteins. Therefore, even those proteins with only two mapped peptides may be abundant proteins in the cell.