Receptor for Advanced Glycation End ProductsRAGE recognizes sugar-modified proteins, contributing to an inflammatory response that plays a role in diabetes
Even the most innocuous things can be dangerous when used in excess. Sugar is the perfect example. Glucose is absolutely necessary to power our cells, so we need to eat a constant supply of food to stay alive. But if we overdo it, excess glucose can cause serious problems. This is particularly apparent in people with diabetes. Excess sugar in the blood, over many years, damages proteins around the body and leads to life-threatening medical problems.
Glucose and molecules derived from it are mildly reactive compounds that attach to sensitive amino acids in all types of proteins. This most often happens in two steps. First, the sugar reacts with the protein forming a relatively unstable connection. Then, over time, this can undergo additional chemical changes creating more stable modifications termed Advanced Glycation End Products (or AGE for short).
RAGE against AGE
These AGE modifications are recognized by our cells by a cell surface receptor, called quite logically the Receptor for Advanced Glycation End Products (RAGE). The structure shown here, from PDB entry 4lp5 , includes the portion of the receptor that extends from the cell surface. It is composed of three domains connected by flexible linkers. The uppermost domain is the one that recognizes AGE in modified proteins.
Researchers are currently working to discover how the interaction of AGE and RAGE contributes to the medical complications of diabetes. When RAGE is activated, it stimulates the production of molecules that promote inflammation. Unfortunately this can get out of control and lead to damage. Researchers are currently looking for drugs to block the action of RAGE, with goal of reducing this inflammatory damage and slowing down the progression of diabetic complications.
Doctors often use hemoglobin as a test to see how much glycation damage has occurred in a patient over their lifetime. They measure the amount of a modified form of hemoglobin, hemoglobin A1c, that has sugar attached to the end of the beta chains. Sugars also attach to other amino acids as well. The structure shown here, from PDB entry entry 3b75 , has a sugar attached to a lysine deep inside the tetrameric complex.
Exploring the Structure
PDB entry 2l7u includes one domain of RAGE bound to an AGE-modified peptide. As with the hemoglobin shown above, the site of damage is a lysine amino acid in the peptide. The modified amino acid binds to a small pocket on the side of RAGE, ultimately triggering a signal on the inside of the cell. To explore this structure in more detail, click on the image for an interactive JSmol.
June 2015, David Goodselldoi:10.2210/rcsb_pdb/mom_2015_6