Functional dissection of HCMV gB’s autonomous fusion activity provides insights into how polymorphisms in clinical isolates confer distinct characteristics

Chen X, Kropff B, Li J, Sticht H, Mollik M, Sieger M, Ferrazzi F, Goerzer I, Mach M, Thomas M (2026)

Publication Type: Journal article

Publication year: 2026

Journal

Mbio American Society for Microbiology: mBio / American Society for Microbiology

Original Authors: Xiaohan Chen, Barbara Kropff, Jiawen Li, Heinrich Sticht, Madlen Mollik, Marie Sieger, Fulvia Ferrazzi, Irene Görzer, Michael Mach, Marco Thomas

Article Number: e00388-26

DOI: 10.1128/mbio.00388-26

Abstract

Glycoprotein B (gB) serves as the viral fusogen facilitating entry and cell-to-cell spread of human cytomegalovirus (HCMV). Fusion is initiated when gH/gL-containing complexes bind to their receptors, leading to gB’s transition from a metastable prefusion to a stable postfusion conformation. We recently demonstrated that substituting or truncating the carboxy-terminal domain of gB renders it intrinsically fusion-competent; however, the precise mechanisms of gB ectodomain reorganization—likely shared by both gH/gL-dependent and -independent fusion processes—remain unclear. In this study, a dual split protein (DSP)-based cell-cell fusion assay was used to assess the gH/gL-independent fusion activities across five major HCMV gB-genotypes (gB1–gB5). Our results show that gB of VR1814 (gB3) exhibits superior autonomous fusion activity compared to TB40/E (gB1) and AD169 (gB2), while gB from C194A (gB4) and UKNEQAS1 (gB5) were fusion-incompetent. Through domain-swapping and site-directed mutagenesis, we identified substitutions that enhance or abrogate fusion and mapped them onto the available pre- and post-fusion structures of gB. Our analysis uncovered a complex network of intra- and inter-domain interactions involving structural domains I, IV, and V of gB, which are crucial for fusion regulation. Functional characterization of gB polymorphisms from clinical HCMV isolates demonstrated opposing impacts, with some variants remaining inactive, while others conferred fusion competence. Collectively, our findings mechanistically elucidate how specific substitutions within the gB ectodomain of particular HCMV strains markedly alter gH/gL-independent fusogenicity. These insights have profound implications for developing diagnostic tools to detect functionally relevant gB polymorphisms and for optimizing vaccine design.

Authors with CRIS profile

Xiaohan Chen Lehrstuhl für Klinische und Molekulare Virologie Jiawen Li Lehrstuhl für Klinische und Molekulare Virologie Heinrich Sticht Professur für Bioinformatik Marie Sieger Department of Nephropathology Fulvia Ferrazzi Department of Nephropathology Michael Mach Institute of Clinical and Molecular Virology Marco Thomas Institute of Clinical and Molecular Virology

Additional Organisation(s)

Interdisziplinäres Zentrum für Klinische Forschung (IZKF)

Involved external institutions

Medizinische Universität Wien AT Austria (AT)

How to cite

APA:

Chen, X., Kropff, B., Li, J., Sticht, H., Mollik, M., Sieger, M.,... Thomas, M. (2026). Functional dissection of HCMV gB’s autonomous fusion activity provides insights into how polymorphisms in clinical isolates confer distinct characteristics. Mbio. https://doi.org/10.1128/mbio.00388-26

MLA:

Chen, Xiaohan, et al. "Functional dissection of HCMV gB’s autonomous fusion activity provides insights into how polymorphisms in clinical isolates confer distinct characteristics." Mbio (2026).

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