Intramembrane client recognition potentiates the chaperone functions of calnexin

Area of Science:

• Cell Biology
• Biochemistry
• Proteomics

Background:

• Membrane proteins constitute a third of the human proteome and are prone to misfolding.
• Molecular chaperones, like Calnexin (CNX), are crucial for proper membrane protein folding and biogenesis.
• CNX primarily interacts with client proteins via its lectin domain, which binds glycans.

Purpose of the Study:

• To investigate Calnexin's interaction with nonglycosylated membrane proteins.
• To identify novel binding modes and client recognition mechanisms of CNX.
• To understand how intramembrane binding influences CNX's chaperone function.

Main Methods:

• Mass spectrometry to identify CNX interacting partners.
• Experimental and computational approaches to analyze CNX transmembrane domain (TMD) interactions.
• Identification of specific sequence motifs involved in client binding.

Main Results:

• CNX interacts with numerous nonglycosylated membrane proteins, indicating nonlectin binding.
• CNX preferentially binds misfolded membrane proteins through its TMD.
• Specific sequence motifs in the CNX TMD mediate intramembrane client recognition.
• Intramembrane client binding enhances CNX's overall chaperone activity.

Conclusions:

• Calnexin utilizes its transmembrane domain for recognizing and binding misfolded membrane proteins within the lipid bilayer.
• This intramembrane binding mechanism complements CNX's known lectin-based interactions.
• Combined binding modes enable CNX to support the biogenesis of diverse membrane proteomes.