# Novel Staphylococcal Inhibitors of Neutrophil Granule Enzymes

> **NIH NIH R01** · KANSAS STATE UNIVERSITY · 2020 · $288,750

## Abstract

Project Abstract/Summary (Project Description)
 The human body relies on neutrophils to provide a sterilizing innate immune response against bacterial
pathogens. Although neutrophils circulate inside the blood in a quiescent state, they are rapidly activated in
reponse to a number of biochemical patterns which signify either that potential pathogens are present or that
cellular damage has occured. Activation of neutrophils results in remarkable changes in their morphology, and
triggers mobilization and secretion of their cytosolic granules. It is these granules which contain critical
components of the neutrophil’s anti-bacterial arsenal. Two of the most abudant components of these granules
are the enzyme myeloperoxidase (MPO), which converts hydrogen peroxide into cytotoxic hypohalous acids,
and a series of chymotrypsin-like serine proteases (NSPs), which can directly attack the pathogen cell by
cleaving proteins that are either exposed on its surface or secreted into the environment. Together, the combined
action of MPO and NSPs form the foundation of neutrophil-mediated innate defense against invading bacteria.
 As a consequence of host/pathogen co-evolution, the Gram-positive bacterium Staphylococcus aureus
has developed a powerful array of small protein inhibitors that effectively block many of the critical components
of the human innate immune response. In this regard, we recently identified three secreted staphylococcal
proteins, called Eap, EapH1, and EapH2 (denoted “EAP proteins”), which potently inhibit NSPs, as well as a
novel staphylococccal inhibitior of MPO, called SPIN. Through collaborative efforts, we have established that
both EAP proteins and SPIN are required for maximal S. aureus virulence in animal infection models. In this
project, we will use a synergistic series of crystallographic and solution NMR methods, physical biochemistry
approaches, and activity assays to provide detailed structure/function information on these novel staphylococcal
inhibitors of neutrophil granule enzymes. We will accomplish this overall goal through two concurrent Specific
Aims. In the first Aim, we will investigate the structural basis for the selectivity of EAP domains toward NSPs,
examine whether changes in protein dynamics influence EAP/NSP interactions, and define a structure/activity
relationship for NSP inhibition by EAP domain proteins. In the second Aim, we will determine the structural basis
for SPIN/MPO binding, examine whether SPIN undergoes changes in conformation upon interaction with MPO,
and define the biochemical determinants which mediate MPO inhibition by SPIN. Finally, since NSPs and MPO
are known to play signifcant roles in damaging host cells and tissues in a number of human inflammatory
diseases, we will explore whether synthetic peptides based upon the structures of EAP proteins and SPIN bound
to their targets can mimic the therapeutically-valuable activities of these staphylococcal immune evasion
proteins. By completing th...

## Key facts

- **NIH application ID:** 9906231
- **Project number:** 5R01GM121511-04
- **Recipient organization:** KANSAS STATE UNIVERSITY
- **Principal Investigator:** Brian V Geisbrecht
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $288,750
- **Award type:** 5
- **Project period:** 2017-04-01 → 2022-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9906231

## Citation

> US National Institutes of Health, RePORTER application 9906231, Novel Staphylococcal Inhibitors of Neutrophil Granule Enzymes (5R01GM121511-04). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9906231. Licensed CC0.

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