The amount of each of the more than a thousand different glycoproteins in your blood varies widely with the 10 most abundant glycoproteins accounting for 90 percent of the total mass. Finding a protein that isn't in this top 10 is a bit like looking for Waldo if only one rendition of the character remained in a collection of every "Where's Waldo" comic ever produced.
This range of disparity in protein concentration is termed dynamic range, and it makes it more difficult for scientists to identify less-abundant proteins and their matching receptors.
Scientists at Sanford Burnham Prebys and colleagues at Scripps Research Institute published findings July 7, 2025, in Nature Communications demonstrating a strategy for identifying less-abundant proteins that bind with a specific type of receptor termed an endocytic lectin, and namely the mannose receptor Mrc1 (also known as CD206 and MMR). This approach enabled the research team to uncover hundreds of binding partners that together predicted Mrc1's roles in our health.
To boost the signal and overcome the noise of so many proteins appearing at different levels, the investigators employed the prototypical mannose-binding lectin Concanavalin A (ConA) to first enrich for those blood proteins bearing multiple linkages of mannose.
"ConA and Mrc1 both have the same mannose linkage binding properties, however Mrc1 is not available as a similarly active recombinant protein," said Mayank Saraswat, PhD, a senior staff scientist at Sanford Burnham Prebys and co-lead author of the study.
"We isolated proteins that bind ConA from the plasma of normal mice and from mice lacking Mrc1," said Saraswat. "Comparisons revealed an increased sensitivity and selectivity allowing identification of the receptor's ligands as they accumulate in the blood in the absence of Mrc1."
Mrc1 keeps the concentration of various critical blood plasma proteins in a healthy range. It does this by binding to proteins that have been post-translationally modified with mannose, sometimes termed mannosylated proteins. Binding of mannosylated proteins to Mrc1 initiates an endocytic clearance mechanism that limits Mrc1 ligand half-lives and abundance in circulation.
After comparing proteins in the bloodstreams of normal mice and mice lacking Mrc1, the team found the accumulation of 244 mannosylated blood plasma proteins to double or more of the amounts found in normal mice due to Mrc1 no longer keeping the levels in check.
The scientists then took a closer look at the newly identified ligands. They used bioinformatics to review and depict these hundreds of proteins by their functions.
"We noticed that a lot of the proteins had very important roles to play," said Jamey Marth, PhD , a professor at Sanford Burnham Prebys and senior and corresponding author of the manuscript. "Renin and angiotensin converting enzyme, for example, are major regulators of blood pressure."
The researchers dug deeper on eight of these proteins known to affect blood pressure, inflammation, organ function and sepsis.
"We observed the disruption of normal physiology and function that was entirely predictable from the identities of the mannosylated proteins accumulating, with the added effect of disease tracking with chronological age," said Marth.
In the case of sepsis, mice lacking Mrc1 perished more quickly from the condition.
"When we looked at samples of blood from human sepsis patients, we found that there was a difference in the proteins that were accumulating when compared to the Mrc1-deficient mice," said Saraswat. "However, when we compared the pathways controlled by these proteins, half of those activated in human sepsis were also activated by Mrc-1 dysfunction."
"To understand the part that glycosidic linkages are playing in health and disease by modifying the abundance and activity of blood glycoproteins, we need to decipher this new language spanning protein glycosylation, detect abnormalities and determine how this system translates in the body to affect different physiological functions," said Saraswat.
Damien Restagno, PhD, a research scientist focused on immunology at Charles River Laboratories, shares first authorship of the study with Saraswat.
John Hintze, PhD, a postdoctoral associate in the Marth lab at Sanford Burnham Prebys, is a co-corresponding author of the manuscript.
Additional authors include:
- Peter V. Aziz and Kathryn Smith from Sanford Burnham Prebys
- Amanda J. Roberts from Scripps Research Institute
The study was supported by the National Institutes of Health and the Independent Research Fund of Denmark.
The study's DOI is 10.1038/s41467-025-61346-4 .
