Transport of proteins into the nucleus occurs via a channel called nuclear pore complex (NPC), which penetrates and spans the nuclear envelope, a double membrane that separates the nucleus from the cytoplasm. The outer nuclear membrane is continuous with the endoplasmic reticulum, hence giving a shorter pathway for proteins to enter the nucleus; inner nuclear membrane contains proteins acting as binding site for nuclear lamina, indirectly providing support for the NPC as the primary function of nuclear lamina is to structurally support the nuclear envelope.
NPC is made up of approximately 30 different proteins known as nucleoporins. There are three types of nucleoporins: 1. Transmembrane ring proteins, which anchor NPC onto nuclear envelope; 2. Scaffold nucleoporins, which give NPC a ring-shaped curvature due to their membrane- bending properties; 3. Channel nucleoporins that line the NPC pore, composing mainly hydrophobic phenylalanine(F) - glycine(G) repeats. Transport of proteins into the nucleus from cytosol occurs via gated transport. For this transport to occur, the amino acids sequence of the proteins must contain a signal sequence deemed as nuclear localization sequence (NLS). Recognition of the sequence is achieved by …show more content…
The complex then diffuse down the NPC into the nucleoplasm, where the importin binds to the Ran-GTP, bringing about a conformational change in the importin, inducing its decreased affinity for the NLS. This enables the release of the cargo protein into the nucleoplasm and the import of protein into nucleus has been achieved. It is not at all times, however, that nuclear import receptors will bind directly to the cargo protein, on some occasion additional adaptor proteins bind to both import receptors and the NLS-bearing proteins, acting as bridge, forming a trimolecular cargo complex as a
NPC is made up of approximately 30 different proteins known as nucleoporins. There are three types of nucleoporins: 1. Transmembrane ring proteins, which anchor NPC onto nuclear envelope; 2. Scaffold nucleoporins, which give NPC a ring-shaped curvature due to their membrane- bending properties; 3. Channel nucleoporins that line the NPC pore, composing mainly hydrophobic phenylalanine(F) - glycine(G) repeats. Transport of proteins into the nucleus from cytosol occurs via gated transport. For this transport to occur, the amino acids sequence of the proteins must contain a signal sequence deemed as nuclear localization sequence (NLS). Recognition of the sequence is achieved by …show more content…
The complex then diffuse down the NPC into the nucleoplasm, where the importin binds to the Ran-GTP, bringing about a conformational change in the importin, inducing its decreased affinity for the NLS. This enables the release of the cargo protein into the nucleoplasm and the import of protein into nucleus has been achieved. It is not at all times, however, that nuclear import receptors will bind directly to the cargo protein, on some occasion additional adaptor proteins bind to both import receptors and the NLS-bearing proteins, acting as bridge, forming a trimolecular cargo complex as a