# Molecular Assembly on the Cell Surface of Actinomyces

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA LOS ANGELES · 2021 · $401,356

## Abstract

PROJECT SUMMARY
Dental plaque represents one of the most complex microbial communities or biofilms known to afflict man. Oral
biofilm-related diseases, e.g. dental carries, gingivitis, periodontitis, and candidosis, impact a large population of
all age groups and continue to impose a huge economic burden due to the lack of effective therapies. The
development of dental plaque begins with the attachment of early bacterial colonizers to the tooth enamel,
generating an adhesive matrix that then attracts intermediate and late colonizers. Actinomyces spp. are key early
colonizers that play a prominent role in biofilm development by virtue of their ability to directly interact not only
with the tooth surface but also with a number of both early and intermediate colonizers. Therefore, our studies
have focused on dissecting the adhesive properties, i.e. fimbriae and non-fimbrial proteins, dictating these
interactions and the mechanism of their assembly on the surface of Actinomyces oris – the most abundant
Actinomyces in the human oral cavity. During the past grant period, we identified the major co-aggregation factor
named CafA, which mediates A. oris interaction with oral streptococci. Remarkably, CafA is found at the tip of a
distinct fimbrial structure made of the pilus shaft FimA, although cafA is not genetically linked to the type 2 fimbrial
gene cluster fimB-fimA-srtC2. Significantly, we found that spatial positioning of the pilus tip adhesin CafA is
essential for CafA-mediated bacterial coaggregation and this process requires the housekeeping sortase SrtA.
We also discovered a small membrane protein named SafA, conserved in the Actinomycetales order, which is
critical for SrtA membrane association. Investigations into the essential nature of srtA revealed the convergence
of two conserved pathways, SrtA-catalyzed cell wall anchoring and LytR-CpsA-Psr (LCP)-mediated
glycosylation, on the cell wall anchored glycoprotein GspA, itself critical for A. oris formation of mono- and multi-
species biofilms and membrane integrity. Thus, we propose that SrtA is the fulcrum for molecular assembly on
the cell surface of Actinomyces. Using biochemical, genetic electron microscopic, and structural approaches, we
aim to test this central hypothesis by examining the mechanism of pilus hijacking and polymicrobial interactions
mediated by the major co-aggregation factor CafA in A. oris, elucidating the mechanism of SrtA modulation of
CafA spatial positioning and CafA-mediated coaggregation, and examining the glycosylation mechanism of the
cell wall anchored GspA that contributes to biofilm formation and membrane integrity. The conservation of
sortase-mediated surface assembly in Gram-positive bacteria and the utilization of srtA essentiality for inhibitor
screens in other Gram-positive pathogens thus magnify the significance of our studies on how sortase SrtA
modulates polymicrobial interactions via surface display of adhesive factors.

## Key facts

- **NIH application ID:** 10240313
- **Project number:** 5R01DE017382-14
- **Recipient organization:** UNIVERSITY OF CALIFORNIA LOS ANGELES
- **Principal Investigator:** Hung Ton-That
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $401,356
- **Award type:** 5
- **Project period:** 2008-02-19 → 2023-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10240313

## Citation

> US National Institutes of Health, RePORTER application 10240313, Molecular Assembly on the Cell Surface of Actinomyces (5R01DE017382-14). Retrieved via AI Analytics 2026-05-21 from https://api.ai-analytics.org/grant/nih/10240313. Licensed CC0.

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