# Structure/Function/Relationship at Single Residue Resolution of the FcRn Transmembrane and Tail

> **NIH NIH F32** · BOSTON CHILDREN'S HOSPITAL · 2020 · $67,446

## Abstract

PROJECT SUMMARY
The goal of this proposal is to map the protein-structure-functional relationships of the rapidly recycling Fcg-
receptor FcRn; and explain its biology.
Highly conserved sequences in the TM and cytosolic tail of FcRn indicate structural interactions with the
membrane necessary for FcRn function. We propose studies utilizing advances in large-scale oligonucleotide
synthesis, multi-parameter FACS, and next-generation sequencing to quantitatively determine the contribution
of FcRn structure to IgG recycling. We will utilize a lentiviral FcRn-expression library that is enabled for Illumina
deep sequencing. The library includes non-biased mutations in the TM or cytosolic FcRn domains that
incorporate 19 different amino acid substitutions for every native residue (67 residues in total) - while otherwise
keeping the rest of the protein as wild type. We will have several thousand cells expressing each mutation and
comparison of the mutants ability to recycle IgG, as compared to WT, will determine the significance of the
mutation. We will use this novel method to test hypothesis-driven mutations to delineate structural features in
the TM region that contribute to efficient endosome recycling and transcytosis. Localization of membrane
proteins can be influenced by properties such as TM length. We will also determine if FcRn use different
dimerization motifs, to switch between functional dimers, as has been shown for other proteins. We will use this
technology to delineate individual residues, motifs, or linkages in the highly conserved cytoplasmic domain that
assists efficient endosome recycling and transcytosis. Research suggests an juxtamembrane amphipathic helix
may sense/induce curvature. There are also several small likely motifs (YXXΦ, acidic di-leucine, CaM-binding,
phosphorylation sites) that will be probed by systematic helix insertions/deletions/scrambling. We will perform
this lentiviral screen across cell types; the comparison of those results will provide information on the generality
or specificity of the mutational hits. Both the hypothesis-driven mutations, and the discoveries from the non-
biased mutations will be further characterized with recycling and transcytosis assays used in our lab. The high-
resolution map produced will provide broad utility for the field, serving as a template by which to interrogate the
membrane-structure/function relationships that govern in any protein where function is amenable to FACS-based
single-cell readout and sorting. As importantly, this project will expand my training in cell and membrane biology
relevant to human diseases and put me in a position to meaningfully extend my career in the life sciences.

## Key facts

- **NIH application ID:** 9911979
- **Project number:** 5F32DK121518-02
- **Recipient organization:** BOSTON CHILDREN'S HOSPITAL
- **Principal Investigator:** Jamie S LeBarron
- **Activity code:** F32 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $67,446
- **Award type:** 5
- **Project period:** 2019-05-01 → 2022-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9911979

## Citation

> US National Institutes of Health, RePORTER application 9911979, Structure/Function/Relationship at Single Residue Resolution of the FcRn Transmembrane and Tail (5F32DK121518-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9911979. Licensed CC0.

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