# Lipoprotein trafficking to the bacterial outer membrane

> **NIH NIH R35** · EMORY UNIVERSITY · 2020 · $386,626

## Abstract

ABSTRACT
Gram-negative bacteria produce an outer membrane (OM) that envelopes the cell. The OM is an essential
organelle and a potent permeability barrier that blocks the entry of many antibiotics into the cell. This barrier
limits clinical options for treating Gram-negative infections at a time of escalating resistance to effective
therapeutics. The OM is separated from the inner membrane by a periplasmic space. All the components of the
OM are delivered across the periplasm to molecular machines that assemble them into the OM bilayer.
Lipoproteins (lipid-anchored proteins) are key to OM assembly. Each of the essential OM assembly machines
require at least one OM lipoprotein for function. After being secreted from the cytosol, nascent lipoproteins are
modified with three acyl chains, anchoring them into the inner membrane. The cell must subsequently traffic
these highly hydrophobic lipoproteins through an unfavorable aqueous periplasmic environment towards the OM
and anchor them into that membrane. Our goal is to understand the mechanisms of lipoprotein trafficking. The
“Lol pathway” in Escherichia coli has served as the paradigm for how lipoproteins are trafficked by Gram-negative
bacteria: the periplasmic protein LolA delivers lipoproteins to the OM where LolB anchors them into the
membrane. We discovered recently that while LolA and LolB are important for efficient trafficking, neither protein
is essential for lipoprotein trafficking and both proteins can be deleted. In their absence, there is no known
mechanism to explain how lipoproteins reach the OM. We aim to uncover the factors behind the LolAB-
independent alternate lipoprotein trafficking route. We will pair classical genetics with high-throughput genomics
to identify genes that are important for fitness and OM biogenesis when LolAB are deleted. We expect such
genes will encode either novel trafficking factors or factors that alleviate stress caused by defects in trafficking.
Complementary biochemical studies will aim to directly capture new lipoprotein trafficking factors in action. We
also aim to exploit our recent discoveries to offer new insights into LolA and LolB function. Now that we have
identified a way to make LolAB conditionally non-essential, we are uniquely placed to thoroughly dissect the
molecular mechanisms employed by these proteins. Our studies will broaden the understanding of lipoprotein
trafficking in Gram-negative bacteria. Given that lipoproteins are essential for all aspect of OM assembly, our
insights will inform the development of novel antibacterial strategies.

## Key facts

- **NIH application ID:** 9984437
- **Project number:** 5R35GM133509-02
- **Recipient organization:** EMORY UNIVERSITY
- **Principal Investigator:** Marcin Grabowicz
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $386,626
- **Award type:** 5
- **Project period:** 2019-08-01 → 2024-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9984437

## Citation

> US National Institutes of Health, RePORTER application 9984437, Lipoprotein trafficking to the bacterial outer membrane (5R35GM133509-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9984437. Licensed CC0.

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