TY - JOUR

T1 - Is Cys(MTSL) the Best α-Amino Acid Residue to Electron Spin Labeling of Synthetically Accessible Peptide Molecules with Nitroxides?

AU - Biondi, Barbara

AU - Syryamina, Victoria N.

AU - Rocchio, Gabriele

AU - Barbon, Antonio

AU - Formaggio, Fernando

AU - Toniolo, Claudio

AU - Raap, Jan

AU - Dzuba, Sergei A.

N1 - Funding Information: V.N.S. and S.A.D. acknowledge financial support from the Russian Science Foundation, project # 21-13-00025. B.B. and F.F. are grateful to the Italian Ministry of Research (PRIN 2020 N. 2020833Y75) and to the University of Padova and Fresenius Kabi iPSUM (Uni-Impresa 2019 PEPTIND) for their financial support. Publisher Copyright: © 2022 The Authors. Published by American Chemical Society

PY - 2022/2/15

Y1 - 2022/2/15

N2 - Electron paramagnetic resonance spectroscopy, particularly its pulse technique double electron–electron resonance (DEER) (also termed PELDOR), is rapidly becoming an extremely useful tool for the experimental determination of side chain-to-side chain distances between free radicals in molecules fundamental for life, such as polypeptides. Among appropriate probes, the most popular are undoubtedly nitroxide electron spin labels. In this context, suitable biosynthetically derived, helical regions of proteins, along with synthetic peptides with amphiphilic properties and antibacterial activities, are the most extensively investigated compounds. A strict requirement for a precise distance measurement has been identified in a minimal dynamic flexibility of the two nitroxide-bearing α-amino acid side chains. To this end, in this study, we have experimentally compared in detail the side-chain mobility properties of the two currently most widely utilized residues, namely, Cys(MTSL) and 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC). In particular, two double-labeled, chemically synthesized 20-mer peptide molecules have been adopted as appropriate templates for our investigation on the determination of the model intramolecular separations. These double-Cys(MTSL) and double-TOAC compounds are both analogues of the almost completely rigid backbone peptide ruler which we have envisaged and 3D structurally analyzed as our original, unlabeled compound. Here, we have clearly found that the TOAC side-chain labels are largely more 3D structurally restricted than the MTSL labels. From this result, we conclude that the TOAC residue offers more precise information than the Cys(MTSL) residue on the side chain-to-side chain distance distribution in synthetically accessible peptide molecules.

AB - Electron paramagnetic resonance spectroscopy, particularly its pulse technique double electron–electron resonance (DEER) (also termed PELDOR), is rapidly becoming an extremely useful tool for the experimental determination of side chain-to-side chain distances between free radicals in molecules fundamental for life, such as polypeptides. Among appropriate probes, the most popular are undoubtedly nitroxide electron spin labels. In this context, suitable biosynthetically derived, helical regions of proteins, along with synthetic peptides with amphiphilic properties and antibacterial activities, are the most extensively investigated compounds. A strict requirement for a precise distance measurement has been identified in a minimal dynamic flexibility of the two nitroxide-bearing α-amino acid side chains. To this end, in this study, we have experimentally compared in detail the side-chain mobility properties of the two currently most widely utilized residues, namely, Cys(MTSL) and 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC). In particular, two double-labeled, chemically synthesized 20-mer peptide molecules have been adopted as appropriate templates for our investigation on the determination of the model intramolecular separations. These double-Cys(MTSL) and double-TOAC compounds are both analogues of the almost completely rigid backbone peptide ruler which we have envisaged and 3D structurally analyzed as our original, unlabeled compound. Here, we have clearly found that the TOAC side-chain labels are largely more 3D structurally restricted than the MTSL labels. From this result, we conclude that the TOAC residue offers more precise information than the Cys(MTSL) residue on the side chain-to-side chain distance distribution in synthetically accessible peptide molecules.

UR - http://www.scopus.com/inward/record.url?scp=85124080149&partnerID=8YFLogxK

U2 - 10.1021/acsomega.1c06227

DO - 10.1021/acsomega.1c06227

M3 - Article

C2 - 35187331

AN - SCOPUS:85124080149

VL - 7

SP - 5154

EP - 5165

JO - ACS Omega

JF - ACS Omega

SN - 2470-1343

IS - 6

ER -