Classes of ER Membrane Proteins

What defines a Type I ER membrane protein?

It has an N-terminal signal sequence and a single transmembrane domain with the N-terminus in the lumen.

What defines Type II and III ER membrane proteins?

They use internal signal-anchor sequences to determine their orientation across the membrane.

What are hydrophobic tail-anchored proteins?

Proteins that are anchored in the membrane by a hydrophobic tail near the C-terminus.

What is a GPI-anchored protein?

A protein initially synthesized as a transmembrane protein that is later transferred to a GPI lipid anchor on the membrane surface.