# HIV-1 Env structure and function assessed by parallel smFRET and cryoET

> **NIH NIH R01** · YALE UNIVERSITY · 2022 · $838,123

## Abstract

HIV-1 Env protein structure and function assessed by parallel smFRET and cryoET
Summary
The HIV-1 Env protein mediates virus entry into cells by promoting fusion between viral and cellular
membranes. As the only virus protein on the surface of virus particles, HIV-1 Env is also a major target for
vaccines. The greatest barriers to the development of a vaccine have been the high sequence variability of
Env, its dense glycan shield and conformational dynamics. We have applied smFRET imaging to gain insights
into the conformational states and conformational dynamics of individual Env protomers in the context of the
native trimer on the surface of intact virions. Our work has revealed that Env opens from a pre-triggered
conformation (State 1) through a necessary intermediate (State 2), into a three CD4 receptor-bound
conformation (State 3). Many broadly neutralizing antibodies (bNAbs) generated by few patients were found to
exhibit a preference for State 1. Associating these conformational states with existing high-resolution
structures, we made the surprising observation that the constructs upon which extant high-resolution structures
are based predominantly occupy the downstream State 2 conformation. Hence, the high-resolution structure of
the pre-triggered State 1 Env, the predominant conformational state of Env on the surface of viruses, which is
preferentially recognized by most broadly neutralizing antibodies (bNAbs) - and thus of central vaccine
importance - remains unknown. To validate and explore these unexpected findings we propose to combine
smFRET with other structural methods to gain a comprehensive understanding of the structure and dynamics
of the native trimer on the surface of intact virions. Towards this end we have established closely knit
collaborations between our existing Mothes/Blanchard team and the laboratory of Dr. Jun Liu to determine the
structure of the HIV-1 Env trimer in its distinct states, including State 1, on the surface of virions by cryo-
electron tomography (cryoET). Leveraging the inherent synergies of smFRET and cryoET, we will capture and
determine structural intermediates of viral entry during membrane fusion.

## Key facts

- **NIH application ID:** 10425409
- **Project number:** 5R01AI150560-04
- **Recipient organization:** YALE UNIVERSITY
- **Principal Investigator:** Scott C Blanchard
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $838,123
- **Award type:** 5
- **Project period:** 2019-07-18 → 2023-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10425409

## Citation

> US National Institutes of Health, RePORTER application 10425409, HIV-1 Env structure and function assessed by parallel smFRET and cryoET (5R01AI150560-04). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10425409. Licensed CC0.

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