TY - JOUR

T1 - Protein Dynamics Enables Phosphorylation of Buried Residues in Cdk2/Cyclin-A-Bound p27

AU - Henriques, João

AU - Lindorff-Larsen, Kresten

PY - 2020

Y1 - 2020

N2 - Proteins carry out a wide range of functions that are tightly regulated in space and time. Protein phosphorylation is the most common post-translation modification of proteins and plays a key role in the regulation of many biological processes. The finding that many phosphorylated residues are not solvent exposed in the unphosphorylated state opens several questions for understanding the mechanism that underlies phosphorylation and how phosphorylation may affect protein structures. First, because kinases need access to the phosphorylated residue, how do such buried residues become modified? Second, once phosphorylated, what are the structural effects of phosphorylation of buried residues, and do they lead to changed conformational dynamics? We have used the ternary complex between p27Kip1 (p27), Cdk2, and cyclin A to study these questions using enhanced sampling molecular dynamics simulations. In line with previous NMR and single-molecule fluorescence experiments, we observe transient exposure of Tyr88 in p27, even in its unphosphorylated state. Once Tyr88 is phosphorylated, we observe a coupling to a second site, thus making Tyr74 more easily exposed and thereby the target for a second phosphorylation step. Our observations provide atomic details on how protein dynamics plays a role in modulating multisite phosphorylation in p27, thus supplementing previous experimental observations. More generally, we discuss how the observed phenomenon of transient exposure of buried residues may play a more general role in regulating protein function.

AB - Proteins carry out a wide range of functions that are tightly regulated in space and time. Protein phosphorylation is the most common post-translation modification of proteins and plays a key role in the regulation of many biological processes. The finding that many phosphorylated residues are not solvent exposed in the unphosphorylated state opens several questions for understanding the mechanism that underlies phosphorylation and how phosphorylation may affect protein structures. First, because kinases need access to the phosphorylated residue, how do such buried residues become modified? Second, once phosphorylated, what are the structural effects of phosphorylation of buried residues, and do they lead to changed conformational dynamics? We have used the ternary complex between p27Kip1 (p27), Cdk2, and cyclin A to study these questions using enhanced sampling molecular dynamics simulations. In line with previous NMR and single-molecule fluorescence experiments, we observe transient exposure of Tyr88 in p27, even in its unphosphorylated state. Once Tyr88 is phosphorylated, we observe a coupling to a second site, thus making Tyr74 more easily exposed and thereby the target for a second phosphorylation step. Our observations provide atomic details on how protein dynamics plays a role in modulating multisite phosphorylation in p27, thus supplementing previous experimental observations. More generally, we discuss how the observed phenomenon of transient exposure of buried residues may play a more general role in regulating protein function.

U2 - 10.1016/j.bpj.2020.06.040

DO - 10.1016/j.bpj.2020.06.040

M3 - Journal article

C2 - 33147476

AN - SCOPUS:85094610294

VL - 119

SP - 2010

EP - 2018

JO - Biophysical Journal

JF - Biophysical Journal

SN - 0006-3495

IS - 10

ER -