Transmembrane domain

These include: Transmembrane helices are visible in structures of membrane proteins determined by X-ray diffraction.

However, membrane pumps and ion channels also contain numerous charged and polar residues within the generally non-polar transmembrane segments.

Once translation is completed, the tail-anchored TMD remains in the ribosomal exit tunnel, and an ATPase mediates targeting to the endoplasmic reticulum.

Quality control of membrane proteins involve TMD-binding factors that are linked to ubiquitination proteasome system.

Once transported, factors assist with insertion of the TMD across the hydrophilic layer phosphate "head" group of the phospholipid membrane.

The signal recognition particle transports membrane proteins to the Sec translocation channel, positioning the ribosome exit tunnel proximal to the translocon central pore and minimizing exposure of the TMD to cytosol.