juxtamembrane

Juxtamembrane is a term used in cell biology to describe regions of proteins or other macromolecules that lie immediately adjacent to a biological membrane. The term derives from the Latin juxta, meaning near, and membrana, meaning membrane. In membrane proteins, the juxtamembrane region typically follows the transmembrane segment and is located on the cytoplasmic side, though the exact orientation can vary with protein topology. This region is often short and lacks a spanning function of its own, but it plays important regulatory roles.

Function and significance: Juxtamembrane domains frequently contribute to how a protein associates with the membrane and how its activity is controlled. They can act as autoinhibitory or activating elements, transmitting conformational changes from the membrane-proximal area to the intracellular domain that carries enzymatic or signaling functions. The juxtamembrane region can also serve as a docking site for kinases, phosphatases, or adaptor proteins, helping to recruit components of signaling cascades. Phosphorylation or other post-translational modifications within this region are common mechanisms that modulate interactions and signal output.

Examples: In receptor tyrosine kinases, the juxtamembrane segment is a key regulator of kinase activity and receptor activation; alterations in this region can change signaling outcomes and are implicated in disease. Juxtamembrane segments also appear in other membrane proteins, including some ion channels and adhesion receptors, where they influence gating, localization, or interactions with cytoplasmic partners.

See also: transmembrane domain, cytoplasmic tail, signal transduction.