kalnexin

Kalnexin is a protein that plays a crucial role in the endoplasmic reticulum, a vital organelle within eukaryotic cells responsible for protein folding, modification, and transport. Specifically, kalnexin is a type I transmembrane protein, meaning it is embedded within the membrane of the endoplasmic reticulum with a portion extending into the lumen (the interior space) and another portion facing the cytoplasm. Its primary function is as a lectin-like chaperone, meaning it binds to specific sugar structures (glycans) attached to newly synthesized proteins. This binding interaction is essential for ensuring that proteins fold correctly.

Kalnexin's chaperone activity is part of a quality control system within the endoplasmic reticulum. When a protein enters the ER, it undergoes glycosylation, the addition of sugar chains. Kalnexin recognizes a specific part of these sugar chains, the monoglucosylated form, and binds to the unfolded or misfolded protein. This binding retains the protein within the ER, preventing its premature exit and allowing it more time to fold properly. If a protein fails to fold correctly, it may be retained by kalnexin and eventually targeted for degradation. Conversely, once a protein achieves its correct three-dimensional structure, it is released from kalnexin and can proceed through the cellular secretory pathway. This precise mechanism is vital for maintaining cellular health and function.