# Initiation of HIV Capsid Assembly Monitored by Mass Photometry

> **NIH NIH R21** · SCRIPPS RESEARCH INSTITUTE, THE · 2024 · $271,500

## Abstract

SUMMARY
This proposal outlines a plan to characterize the early steps of HIV-1 capsid assembly using a novel and
recently available single molecule technique. The earliest steps include association of myristoylated Gag (myr-
Gag) with the plasma membrane, oligomerization of Gag, and recruitment of dimeric viral genomic RNA. There
is a large literature on the early steps, but the in vitro biochemical data has primarily focused on studies
involving two of the three required components: protein, RNA, and lipid. Here, we propose to use mass
photometry (MP) to study Gag-Gag and Gag-RNA interactions in a model lipid membrane system, namely
supported lipid bilayers (SLBs). Mass photometry is a relatively new method to characterize the distribution of
molecular weights (MW) in a sample using interferometry of scattered light. Data can be recorded either as a
“landing assay” observing molecules adsorbing to a surface non-specifically, or as a “dynamic assay”,
observing molecules diffusing on an SLB. In the landing assay, the distribution of MW for molecules
associating/dissociating from the surface is measured, providing information on the distribution of oligomeric
states and complexes. In the dynamic assay, both the position and MW of the complexes are recorded as a
function of time. The latter assay provides an unprecedented opportunity to observe Gag and Gag:RNA
complexes in an SLB in a label-free manner.

## Key facts

- **NIH application ID:** 10764316
- **Project number:** 5R21AI176215-02
- **Recipient organization:** SCRIPPS RESEARCH INSTITUTE, THE
- **Principal Investigator:** James R Williamson
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $271,500
- **Award type:** 5
- **Project period:** 2023-01-13 → 2024-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10764316

## Citation

> US National Institutes of Health, RePORTER application 10764316, Initiation of HIV Capsid Assembly Monitored by Mass Photometry (5R21AI176215-02). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10764316. Licensed CC0.

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