The protein was solved using nuclear magnetic resonance (NMR); it contains 87 residues and its molecular weight is 10.182 kDa.
AcrIIA4 contains:
3 antiparallel β-strands (the first, from residues 16 to 19, the second, from 29 to 33, and the third, from 40 to 44) that form a β-sheet.
This represents a 16,1% of the total number of amino acids, as 14 of them form the β-strands.

3 α-helices (the first, 2–13 residues, the second, 50–59 residues, and the third, 68–85 residues).

1 3₁₀ helix placed between the first (β1) and second (β2) β-strands, which starts at residue 22 and end in residue 25.
The total helical part is composed of 40 residues, which is a 50,6% of the protein.

Loops joining the different secondary structures.

There is a good definition of the secondary structures, as the three α-helices are packed near the three β-strands.
Strikingly, between β3 strand, α2 and α3 helices, there is a hydrophobic core, originated by a cluster of aromatic side chains which are attracted by non-covalent interactions, such as pi stacking.
Moreover, as it is an acidic protein, there is a high concentration of negatively charged residues in the loops between β3 and α2, between α2 and α3, and in the first part of α3, which may play an important role in the inhibition of Cas9, as negative charges might imitate phosphates of nucleic acids.
The protein was solved using nuclear magnetic resonance (NMR); it contains 87 residues and its molecular weight is 10.182 kDa. AcrIIA4 contains:
3 antiparallel β-strands (the first, from residues 16 to 19, the second, from 29 to 33, and the third, from 40 to 44) that form a β-sheet. This represents a 16,1% of the total number of amino acids, as 14 of them form the β-strands.
3 α-helices (the first, 2–13 residues, the second, 50–59 residues, and the third, 68–85 residues).
1 3₁₀ helix placed between the first (β1) and second (β2) β-strands, which starts at residue 22 and end in residue 25. The total helical part is composed of 40 residues, which is a 50,6% of the protein.
Loops joining the different secondary structures.
There is a good definition of the secondary structures, as the three α-helices are packed near the three β-strands. Strikingly, between β3 strand, α2 and α3 helices, there is a hydrophobic core, originated by a cluster of aromatic side chains which are attracted by non-covalent interactions, such as pi stacking. Moreover, as it is an acidic protein, there is a high concentration of negatively charged residues in the loops between β3 and α2, between α2 and α3, and in the first part of α3, which may play an important role in the inhibition of Cas9, as negative charges might imitate phosphates of nucleic acids.
Anti-CRISPR