There is of course differences when you compare moles and mass, as proteins like collagen are massive (>1000AA) compared to something like ubiquitin (<100AA). But looking at mass we can guess something like this...
- Collagen (25% of proteins)
- Actin (20% of dry muscle mass)
- Myosin? (second most abundent in muscle) or keratin (most abundent in epithelium/hair)?
- Albumin? (60% of serum protein,and only 40% of all albumin is present in serum)
- Superoxyde dismutase (most abundent in mitochondria)
- Hemoglobin? (95% of RBC dry mass)
- Osteocalcin (second most abundent in bones after collagen)
However, I have not given up on the idea that it should be a bacterial protein considering they have so much biomass, all to way to 2km down the crust and at the bottom of oceans. I would quote Stephen J Gould for this matter : "When one considers how deeply entrenched has been the dogma that most earthly biomass lies in the wood of our trees, this potentially greater weight of underground bacteria represents a major revision of conventional biology and quite a boost for the modal bacter. Not only does the Earth contain more bacterial organisms than all others combined (scarcely surprising, given their minimal size and mass); not only do bacteria live in more places and work in a greater variety of metabolic ways; not only did bacteria alone constitute the first half of life's history, with no slackening in diversity thereafter; but also, and most surprisingly, total bacterial biomass (even at such minimal weight per cell) may exceed all the rest of life combined, even forest trees, once we include the subterranean populations as well."