Limits...
Differences in the transactivation domains of p53 family members: a computational study.

Mavinahalli JN, Madhumalar A, Beuerman RW, Lane DP, Verma C - BMC Genomics (2010)

Bottom Line: Folding simulation studies have been carried out to examine the propensity and stability of this region and are used to understand the differences between the family members with the ease of helix formation following the order p53 > p73 > p63.Differences in these interactions between the family members may partially account for the differential binding to, and regulation by, MDM2 (and MDMX).Phosphorylations of the peptides further modulate the stability of the helix and control associations with partner proteins.

View Article: PubMed Central - HTML - PubMed

Affiliation: Bioinformatics Institute (A-STAR), Matrix, Singapore. jagadeesh@bii.a-star.edu.sg

ABSTRACT
The N terminal transactivation domain of p53 is regulated by ligases and coactivator proteins. The functional conformation of this region appears to be an alpha helix which is necessary for its appropriate interactions with several proteins including MDM2 and p300. Folding simulation studies have been carried out to examine the propensity and stability of this region and are used to understand the differences between the family members with the ease of helix formation following the order p53 > p73 > p63. It is clear that hydrophobic clusters control the kinetics of helix formation, while electrostatic interactions control the thermodynamic stability of the helix. Differences in these interactions between the family members may partially account for the differential binding to, and regulation by, MDM2 (and MDMX). Phosphorylations of the peptides further modulate the stability of the helix and control associations with partner proteins.

Show MeSH
Evolution of secondary structures of the phosphorylated peptide variants of p53 at (A) T18 (B) S20 and (C) T18 and S20; Colour code: purple, α-helix; red, π-helix; yellow, β-sheet; green, isolated bridge; cyan, turn; white, random coil.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2822533&req=5

Figure 8: Evolution of secondary structures of the phosphorylated peptide variants of p53 at (A) T18 (B) S20 and (C) T18 and S20; Colour code: purple, α-helix; red, π-helix; yellow, β-sheet; green, isolated bridge; cyan, turn; white, random coil.

Mentions: The region of p53 investigated here has two phosphorylation sites - T18 and S20. Phosphorylation of T18 resulted in some loss of helical propensity (Figure 8A) compared to that in unphosphorylated p53 and this largely seems to arise because of long range interactions between the phosphate and K24 that prevent helical propagation (Movie S10). However helicity is still retained, albeit reduced, and is in accord with our earlier findings [63]. In contrast, phosphorylation of S20 actually enhances the helical propensity of p53 (Figure 8B). This appears to be stabilized by interactions between the phosphate and K24. The reason why this interaction stabilizes the helix appears to be the spatial proximity of these two in contrast to the case of phosphorylated T18. These folding patterns are consistent with the binding affinity of p53 to MDM2 where only the phosphorylation of T18 attenuates binding to MDM2 [18]. Indeed, the phosphorylation of S20 needs a helical conformation as this appears to be a structural requirement for binding to p300 [64]. When both T18 and S20 are phosphorylated the folding pattern (Figure 8C) seemed to display an initial effect of phosphorylation of T18 (as in Figure 8A) followed by that of S20 (Figure 8B). Consistent with the individual phosphorylations, the pattern of interactions seen upon double phosphorylation is conserved. Recent work has demonstrated that p53 has to be significantly helical to optimally interact with p300 [62] and perhaps even for simultaneous binding to MDM2 and p300 [13]. Our observations also suggest that double phosphorylation does retain the helicity required for binding to p300 and that dephosphorylation of T18 is not required prior to phosphorylation of S20 for such binding events.


Differences in the transactivation domains of p53 family members: a computational study.

Mavinahalli JN, Madhumalar A, Beuerman RW, Lane DP, Verma C - BMC Genomics (2010)

Evolution of secondary structures of the phosphorylated peptide variants of p53 at (A) T18 (B) S20 and (C) T18 and S20; Colour code: purple, α-helix; red, π-helix; yellow, β-sheet; green, isolated bridge; cyan, turn; white, random coil.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2822533&req=5

Figure 8: Evolution of secondary structures of the phosphorylated peptide variants of p53 at (A) T18 (B) S20 and (C) T18 and S20; Colour code: purple, α-helix; red, π-helix; yellow, β-sheet; green, isolated bridge; cyan, turn; white, random coil.
Mentions: The region of p53 investigated here has two phosphorylation sites - T18 and S20. Phosphorylation of T18 resulted in some loss of helical propensity (Figure 8A) compared to that in unphosphorylated p53 and this largely seems to arise because of long range interactions between the phosphate and K24 that prevent helical propagation (Movie S10). However helicity is still retained, albeit reduced, and is in accord with our earlier findings [63]. In contrast, phosphorylation of S20 actually enhances the helical propensity of p53 (Figure 8B). This appears to be stabilized by interactions between the phosphate and K24. The reason why this interaction stabilizes the helix appears to be the spatial proximity of these two in contrast to the case of phosphorylated T18. These folding patterns are consistent with the binding affinity of p53 to MDM2 where only the phosphorylation of T18 attenuates binding to MDM2 [18]. Indeed, the phosphorylation of S20 needs a helical conformation as this appears to be a structural requirement for binding to p300 [64]. When both T18 and S20 are phosphorylated the folding pattern (Figure 8C) seemed to display an initial effect of phosphorylation of T18 (as in Figure 8A) followed by that of S20 (Figure 8B). Consistent with the individual phosphorylations, the pattern of interactions seen upon double phosphorylation is conserved. Recent work has demonstrated that p53 has to be significantly helical to optimally interact with p300 [62] and perhaps even for simultaneous binding to MDM2 and p300 [13]. Our observations also suggest that double phosphorylation does retain the helicity required for binding to p300 and that dephosphorylation of T18 is not required prior to phosphorylation of S20 for such binding events.

Bottom Line: Folding simulation studies have been carried out to examine the propensity and stability of this region and are used to understand the differences between the family members with the ease of helix formation following the order p53 > p73 > p63.Differences in these interactions between the family members may partially account for the differential binding to, and regulation by, MDM2 (and MDMX).Phosphorylations of the peptides further modulate the stability of the helix and control associations with partner proteins.

View Article: PubMed Central - HTML - PubMed

Affiliation: Bioinformatics Institute (A-STAR), Matrix, Singapore. jagadeesh@bii.a-star.edu.sg

ABSTRACT
The N terminal transactivation domain of p53 is regulated by ligases and coactivator proteins. The functional conformation of this region appears to be an alpha helix which is necessary for its appropriate interactions with several proteins including MDM2 and p300. Folding simulation studies have been carried out to examine the propensity and stability of this region and are used to understand the differences between the family members with the ease of helix formation following the order p53 > p73 > p63. It is clear that hydrophobic clusters control the kinetics of helix formation, while electrostatic interactions control the thermodynamic stability of the helix. Differences in these interactions between the family members may partially account for the differential binding to, and regulation by, MDM2 (and MDMX). Phosphorylations of the peptides further modulate the stability of the helix and control associations with partner proteins.

Show MeSH