Submission 45
Structural insight into the function of human peptidyl arginine deiminase 6
Wednesday-Posters 2-Poster-03
Presented by: Jack Williams
Peptidyl arginine deiminase 6 (PADI6) is vital for early embryonic development in mice and humans, yet its function remains elusive. PADI6 is less conserved with the other PADIs, and it is currently unknown whether it has a catalytic function. Towards understanding the function of PADI6, we have determined a 2.44 Å crystal structure of human PADI6, the first high resolution structure of the wild type protein.
We show that human PADI6 dimerises like hPADIs 2-4, however does not bind calcium ions and is inactive in in vitro assays against standard PADI substrates. Our crystal structure reveals that hPADI6 is structured in the absence of calcium ions where hPADI2 and hPADI4 are not, and that the Ca-binding sites are not conserved. Moreover, our structure reveals that whilst the key catalytic aspartic acid and histidine residues are structurally conserved, the cysteine is displaced far from the active site centre. The hPADI6 active site pocket appears closed through a unique evolved mechanism in hPADI6, not present in the other PADIs. Finally, with a high-resolution X-ray crystal structure of hPADI6 in hand, we investigated the structural consequences of the reported clinically significant variants by modelling biallelic structural damage scores for variants reported to cause infertility, hydatidiform mole formation, and multi-locus imprinting disorders. We show that variants that result in infertility have a higher structural damage score than those that result in imprinting disorders and highlight three single amino acid substitutions reported to cause infertility that indicates PADI6 dimerisation is critical for its function.
Taken together, these findings provide insight into how the function of hPADI6 may differ from the other PADIs based on its structure and provides a resource for characterising the damaging effect of clinically significant PADI6 variants.
We show that human PADI6 dimerises like hPADIs 2-4, however does not bind calcium ions and is inactive in in vitro assays against standard PADI substrates. Our crystal structure reveals that hPADI6 is structured in the absence of calcium ions where hPADI2 and hPADI4 are not, and that the Ca-binding sites are not conserved. Moreover, our structure reveals that whilst the key catalytic aspartic acid and histidine residues are structurally conserved, the cysteine is displaced far from the active site centre. The hPADI6 active site pocket appears closed through a unique evolved mechanism in hPADI6, not present in the other PADIs. Finally, with a high-resolution X-ray crystal structure of hPADI6 in hand, we investigated the structural consequences of the reported clinically significant variants by modelling biallelic structural damage scores for variants reported to cause infertility, hydatidiform mole formation, and multi-locus imprinting disorders. We show that variants that result in infertility have a higher structural damage score than those that result in imprinting disorders and highlight three single amino acid substitutions reported to cause infertility that indicates PADI6 dimerisation is critical for its function.
Taken together, these findings provide insight into how the function of hPADI6 may differ from the other PADIs based on its structure and provides a resource for characterising the damaging effect of clinically significant PADI6 variants.