# T4SS effectors and tick tropism in Anaplasma phagocytolium

> **NIH NIH R21** · WASHINGTON STATE UNIVERSITY · 2020 · $191,250

## Abstract

Project Summary
 Tick-borne diseases are on the increase, and are responsible for nearly all of the vector-transmitted disease
in the US. Vector-borne pathogens face the dual challenge of adaptation to two very different host environments:
the arthropod vector and the mammalian host. To survive within eukaryotic cells, the rickettsial pathogen
Anaplasma phagocytophilum blocks phago-lysosome maturation, inhibits apoptosis, modulates host gene
expression, redirects trans-Golgi trafficking, and repurposes autophagic machinery to build a replication vacuole.
A. phagocytophilum must accomplish this, all while evading the unique innate immune defenses of mammalian
and arthropod host cells. All pathogens in the order Rickettsiales utilize a specialized Type IV Secretion System
(T4SS) to deliver effector molecules into the host cell cytosol to mediate host pathogen interactions. However,
identification of the secreted effectors has been limited by the obligate nature of these pathogens. Even less is
known about how effectors contribute to rickettsial growth in tick cells, as the tick vector remains an understudied
niche of these pathogens. To overcome this, our group has developed a T4SS effector prediction program
Optimal-features Predictor for T4SS Effectors (OPT4e). When applied to A. phagocytophilum, OPT4e identified
48 putative T4SS effectors. Transcriptomics finds that 15 of these predicted effector genes are specifically
expressed during growth within either tick or mammalian cells. We have demonstrated that one of these tick-
specific effector candidates, Aph1383, is translocated in a T4 specific manner by the Legionella pneumophila
T4SS. Aph1383 also belongs to a paralogous family of six proteins encoded by the gene cluster aph1380-1386.
This entire cluster is expressed 2.5-fold more highly during A. phagocytophilum growth in tick cells than during
mammalian cell infections. We hypothesize that this family of Aph1383 paralogs are all T4SS effectors which
target host cell processes specifically important for A. phagocytophilum growth within tick cells. In this study, we
will first use transposon insertion mutants in the aph1380-1386 gene cluster to test the fitness contribution of
these genes during A. phagocytophilum growth within tick cells. Next, we will evaluate the T4SS translocation of
all Aph1383 paralogs and identify the amino acid sequences necessary for secretion. Finally, we will identify the
subcellular localization and molecular targets of Aph1383 within tick cells. Characterizing these molecular
interactions of A. phagocytophilum within the tick cell will open the door to development of vector targeted
interventions to reduce transmissibility of the pathogen.

## Key facts

- **NIH application ID:** 10041492
- **Project number:** 1R21AI154023-01
- **Recipient organization:** WASHINGTON STATE UNIVERSITY
- **Principal Investigator:** Kelly Ann Brayton
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $191,250
- **Award type:** 1
- **Project period:** 2020-06-01 → 2022-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10041492

## Citation

> US National Institutes of Health, RePORTER application 10041492, T4SS effectors and tick tropism in Anaplasma phagocytolium (1R21AI154023-01). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10041492. Licensed CC0.

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