User:Davi de Souza/Sandbox 1

Structure

Functional domains and their roles

Using the as a model of study, it is possible to see that the protein has . Domains 1 and 2 are responsible for binding to N-glycosylated phosphatidylinositol (GPI) proteins, which are present in the membranes of eukaryotic cells. binds to specific sugar modifications found on the GPI, while directly binds to the glycan core located in the central portion of GPI proteins. Therefore, both domain 1 and domain 2 are involved in anchoring the aerolysin proprotein to the target cell membrane. is composed of a five-stranded beta sheet and a , which are important for the insertion and anchoring of the protein into the cell membrane. is an extension of the beta sheet from domain 3, but it is opened by the , forming a twisted double-fold in the beta sheet. This conformational change induced by the CTP propeptide allows the protein to fold into its soluble form.^[2]

Structure highlights of the Aerolysin Oligomer

When the CTP is cleaved from the main body of the protein, the proaerolisin oligomerizes into a heptameric ring on the target cell membrane, forming a pore. During proaerolisin oligomerization, domain 1 undergoes rotation, allowing all receptor binding sites to position themselves correctly relative to the target membrane. Domains 2 and 3 remain largely unchanged. On the other hand, domain 4, after cleavage of the CTP propeptide, undergoes rearrangement of the beta sheets, forming a beta sandwich. In the core of this sandwich, hydrophobic residues are internalized. Additionally, domain 4 rotates relative to domain 3, enabling hydrogen bonding between the beta sandwiches of two monomers, promoting the oligomerization of aerolysin.^[3]

The oligomerization of aerolysin, resulting from the circular association of the beta barrels from the seven monomers, forms a (in the image, each color represents the domain 4 of a monomer, forming a tube). It is interesting to note that the beta sheets present in the cylinder are anti-parallel.

(Iacovache, I., De Carlo, S., Cirauqui, N. et al. Cryo-EM structure of aerolysin variants reveals a novel protein fold and the pore-formation process. Nat Commun 7, 12062 (2016). https://doi.org/10.1038/ncomms12062)

Subsequently, domains 3 and 4 twist slightly relative to domains 1 and 2, allowing for the elongation of the inner beta barrel through the addition of amino acids. In the 3D representation of the box next to it, we can observe the phenomenon described above: First showing the , with the domains of a monomer, and then showing the that form the cylindrical tube of the barrel.

Finally, the inner beta barrel elongates with the addition of an additional 15 residues in the pre-stem loop. Additionally, a twist occurs in two regions adjacent to domain 3, located at the base of the beta barrel.

(Iacovache, I., De Carlo, S., Cirauqui, N. et al. A estrutura Cryo-EM de variantes de aerolisina revela uma nova dobra de proteína e o processo de formação de poros. Nat Commun 7, 12062 (2016). https: / /doi.org/10.1038/ncomms12062 )

This twist results in a vertical collapse in the protein, resulting in the extension of the beta barrel. In the 3D representation of the box next to it, we can observe the phenomenon described above: first showing the , with the domains of a monomer, and then showing the that form the cylindrical tube of the barrel.

3D Structures of Aerolysin

Aerolysin 3D structures