# Molecular basis of heme scavenging by Gram-positive bacteria

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA LOS ANGELES · 2024 · $606,938

## Abstract

Project Summary
Nearly all species of bacteria require iron to grow because it is an essential metal cofactor that is used by
microbial enzymes to mediate cellular metabolism. During infections, bacterial pathogens forage iron from
human hemoglobin (Hb) that is released from red blood cells, which contains ∼75–80% of the human body's
total iron content in the form of heme (iron protoporphyrin IX). The basic science studies outlined in this proposal
will determine how the human pathogen Corynebacterium diphtheriae acquires iron from Hb. This work will have
a broad impact, as C. diphtheriae is a model organism within the Actinobacteria phylum, which contains several
species of bacteria that are human pathogens, as well as microbes that are major components of the human
gastrointestinal microbiome. Research will be performed by an established team of investigators that have
complementary expertise in microbiology, proteomics, biochemistry and structural biology. We will determine
how microbial receptors capture Hb and remove its heme, and how cell wall embedded proteins ferry released
heme into the cell. In aim #1, we will determine how C. diphtheriae uses the HbpA receptor to capture Hb on the
cell surface and test the hypothesis that the receptor works in concert with surface associated heme-receptors
to distort Hb and trigger heme release. In aim #2, we will determine the molecular basis through which heme is
passed across the cell wall by determining how widely distributed Conserved Region (CR) domains in
Actinobacteria directly exchange heme by forming low-affinity transfer complexes. In aim #3, we will obtain a
systems-level understanding of the heme uptake process by applying mass spectrometry proteomics methods
to determine each component’s abundance and location, and by developing and applying a novel fluorogenic
Hb-reporter to track heme removal from Hb in cell culture. These studies will enable us to quantitatively assess
the importance of each system component in heme uptake, and to test the hypothesis that they form a molecular
wire through which heme flows to the membrane. The results of these studies will provide fundamental insight
into how C. diphtheriae and other Actinobacteria acquire heme-iron, and develop generalizable tools to study
this process in live bacteria. Combined, the results of this research could lead to new therapeutics to treat
infections caused by antibiotic resistant bacteria that work by disrupting heme import.

## Key facts

- **NIH application ID:** 10752601
- **Project number:** 5R01AI161828-03
- **Recipient organization:** UNIVERSITY OF CALIFORNIA LOS ANGELES
- **Principal Investigator:** Robert Thompson Clubb
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $606,938
- **Award type:** 5
- **Project period:** 2021-01-19 → 2026-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10752601

## Citation

> US National Institutes of Health, RePORTER application 10752601, Molecular basis of heme scavenging by Gram-positive bacteria (5R01AI161828-03). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10752601. Licensed CC0.

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