Four IgG Antibodies and Protein G Are Shapeshifters

Glocker, Michael O.; Ruß, Manuela; Koy, Cornelia; Kreutzer, Michael; Melder, Fiona T. I.; Diebler, Yelena; Illges, Harald; Opuni, Kwabena F. M.

doi:10.3390/ijms27177662

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Open AccessArticle

Four IgG Antibodies and Protein G Are Shapeshifters

by

Michael O. Glocker

^1,*

,

Manuela Ruß

¹

,

Cornelia Koy

¹

,

Michael Kreutzer

¹

,

Fiona T. I. Melder

¹

,

Yelena Diebler

¹

,

Harald Illges

²

and

Kwabena F. M. Opuni

^3,4

¹

Proteome Center Rostock, Medical Faculty and Natural Science Faculty, University of Rostock, Schillingallee 69, 18057 Rostock, Germany

²

Department of Applied Natural Sciences, Immunology and Cell Biology, Institute of Functional Gene Analytics, University of Applied Sciences Bonn-Rhein-Sieg, von-Liebig-Str. 20, 53359 Rheinbach, Germany

³

Department of Pharmaceutical Chemistry, School of Pharmacy, College of Health Science, University of Ghana, Legon P.O. Box LG43, Ghana

⁴

Food and Drugs Authority Ghana, Cantonments, Accra P.O. Box CT2783, Ghana

^*

Author to whom correspondence should be addressed.

Int. J. Mol. Sci. 2026, 27(17), 7662; https://doi.org/10.3390/ijms27177662

Submission received: 10 July 2026 / Revised: 19 August 2026 / Accepted: 21 August 2026 / Published: 26 August 2026

(This article belongs to the Special Issue 25th Anniversary of IJMS: Updates and Advances in Macromolecules)

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Abstract

Studying protein structure dynamics is key to understanding protein function modulation. Alternative protein conformations are well discriminated from each other by nanoESI mass spectrometry and ion mobility measurements. Experimentally determined collisional cross-sections were compared to calculated collisional cross-sections of fifteen peptides, single-domain proteins, and protein complexes. The multi-domain proteins investigated here, four immunoglobulin G (IgG) antibodies and protein G, are present as compacted/folded “native” conformations in neutral buffered solutions, and they are identified by molecular ions with narrow charge-state distributions, relatively few charges, and small collisional cross-sections. Simultaneously present extended/folded but nevertheless “native” conformations produced additional ions with higher charge states, different charge-state distributions, and larger collisional cross-sections. Computed collisional cross-sections from compacted “o-shape” and extended “l-shape” protein G three-dimensional (3D) structures match experimental data, indicating equilibrium, and suggest a dynamic “o2l” flip process. Likewise, “m-shape” (compacted) and “Y-shape” (extended) IgGs are regarded as two supposedly reversibly adopted antibody conformations which may interchange by an “m2Y” flip. Adopting an m-shape would prevent an antibody-based initiation of humoral and cellular immune system responses, such as opsonophagocytosis, prior to antigen contact, which stands in line with the rearrangement hypothesis.

Keywords: opsonophagocytosis; IgG; protein G; nanoESI-MS; ion mobility mass spectrometry; collision cross section; biocomputational analysis; molecular modeling; I-TASSER; Pepfold4; AlphaFold3

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MDPI and ACS Style

Glocker, M.O.; Ruß, M.; Koy, C.; Kreutzer, M.; Melder, F.T.I.; Diebler, Y.; Illges, H.; Opuni, K.F.M. Four IgG Antibodies and Protein G Are Shapeshifters. Int. J. Mol. Sci. 2026, 27, 7662. https://doi.org/10.3390/ijms27177662

AMA Style

Glocker MO, Ruß M, Koy C, Kreutzer M, Melder FTI, Diebler Y, Illges H, Opuni KFM. Four IgG Antibodies and Protein G Are Shapeshifters. International Journal of Molecular Sciences. 2026; 27(17):7662. https://doi.org/10.3390/ijms27177662

Chicago/Turabian Style

Glocker, Michael O., Manuela Ruß, Cornelia Koy, Michael Kreutzer, Fiona T. I. Melder, Yelena Diebler, Harald Illges, and Kwabena F. M. Opuni. 2026. "Four IgG Antibodies and Protein G Are Shapeshifters" International Journal of Molecular Sciences 27, no. 17: 7662. https://doi.org/10.3390/ijms27177662

APA Style

Glocker, M. O., Ruß, M., Koy, C., Kreutzer, M., Melder, F. T. I., Diebler, Y., Illges, H., & Opuni, K. F. M. (2026). Four IgG Antibodies and Protein G Are Shapeshifters. International Journal of Molecular Sciences, 27(17), 7662. https://doi.org/10.3390/ijms27177662

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