TY - JOUR

T1 - Evidence for an ordering transition near 120 k in an intrinsically disordered protein, casein

AU - Maslennikova, Natalya A.

AU - Golysheva, Elena A.

AU - Dzuba, Sergei A.

N1 - Funding Information: This work was supported by the Russian Science Foundation, project # 21-13-00025. Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

PY - 2021/10/1

Y1 - 2021/10/1

N2 - Intrinsically disordered proteins (IDPs) are proteins that possess large unstructured re-gions. Their importance is increasingly recognized in biology but their characterization remains a challenging task. We employed field swept Electron Spin Echoes in pulsed EPR to investigate low-temperature stochastic molecular librations in a spin-labeled IDP, casein (the main protein of milk). For comparison, a spin-labeled globular protein, hen egg white lysozyme, is also investigated. For casein these motions were found to start at 100 K while for lysozyme only above 130 K, which was ascribed to a denser and more ordered molecular packing in lysozyme. However, above 120 K, the motions in casein were found to depend on temperature much slower than those in lysozyme. This abrupt change in casein was assigned to an ordering transition in which peptide residues rearrange making the molecular packing more rigid and/or more cohesive. The found features of molecular motions in these two proteins turned out to be very similar to those known for gel-phase lipid bi-layers composed of conformationally ordered and conformationally disordered lipids. This analogy with a simpler molecular system may appear helpful for elucidation properties of molecular packing in IDPs.

AB - Intrinsically disordered proteins (IDPs) are proteins that possess large unstructured re-gions. Their importance is increasingly recognized in biology but their characterization remains a challenging task. We employed field swept Electron Spin Echoes in pulsed EPR to investigate low-temperature stochastic molecular librations in a spin-labeled IDP, casein (the main protein of milk). For comparison, a spin-labeled globular protein, hen egg white lysozyme, is also investigated. For casein these motions were found to start at 100 K while for lysozyme only above 130 K, which was ascribed to a denser and more ordered molecular packing in lysozyme. However, above 120 K, the motions in casein were found to depend on temperature much slower than those in lysozyme. This abrupt change in casein was assigned to an ordering transition in which peptide residues rearrange making the molecular packing more rigid and/or more cohesive. The found features of molecular motions in these two proteins turned out to be very similar to those known for gel-phase lipid bi-layers composed of conformationally ordered and conformationally disordered lipids. This analogy with a simpler molecular system may appear helpful for elucidation properties of molecular packing in IDPs.

KW - Electron spin echo

KW - EPR

KW - Lipid bilayers

KW - Molecular packing

KW - Spin labels

KW - Stochastic molecular librations

UR - http://www.scopus.com/inward/record.url?scp=85116591977&partnerID=8YFLogxK

U2 - 10.3390/molecules26195971

DO - 10.3390/molecules26195971

M3 - Article

C2 - 34641515

AN - SCOPUS:85116591977

VL - 26

JO - Molecules

JF - Molecules

SN - 1420-3049

IS - 19

M1 - 5971

ER -