# Mechanisms of tether function in endolysosomal trafficking - Renewal - Resubmission 01

> **NIH NIH R01** · UNIVERSITY OF CHICAGO · 2020 · $291,916

## Abstract

Project Summary
The accurate trafficking of proteins through membrane compartments depends on the ability of specific
vesicles to recognize one another and undergo efficient fusion. Accuracy is conferred in part by molecular
tethers, which are multivalent complexes that bind to vesicle determinants and foster specific vesicle-vesicle
contacts. Endosome-lysosome trafficking is required for the processing of cargo taken up from the cell surface,
and also paradoxically for the formation of some secretory organelles. Two key tethers involved in
endolysosomal trafficking are CORVET (class C core vacuole/endosome tethering) and HOPS (homotypic
fusion and protein sorting). Both are hetero-hexameric complexes, whose importance in cell and organismal
physiology is shown by the fact that human variants in the genes encoding CORVET/HOPS subunits are linked
with mucopolysaccharidosis, renal dysfunction, neurodegeneration and cancer, among other diseases. At the
cellular level, CORVET and HOPS both function in homotypic fusion, i.e., allow two vesicles with the same Rab
determinants to recognize one another. The mechanisms of action of CORVET/HOPS have been deduced
primarily via in vitro reconstitution experiments. However, key aspects of current models have yet to be tested
in vivo, including important mechanistic details such as whether the complexes are stably associated with
membranes, whether individual complexes undergo cyclical assembly/disassembly, and whether different
subunits have distinct cycling dynamics. In addition, the assembly state of tethers on vesicles is unknown, a
salient question because the tether subunits are structurally similar to coat proteins that form large assemblies
on membranes. In the lineage of ciliates including the model organism Tetrahymena thermophila, the HOPS
complex was lost. Concurrently, CORVET complexes multiplied in these cells, with individual complexes
becoming specialized for distinct endolysosomal pathways. Due to its specific evolutionary history combined
with experimental strengths, Tetrahymena offers a unique new system to analyze these universal tethers.
Issues to be addressed include the copy number of CORVET complexes associated with vesicles, the
dynamics of both the holo-complexes and individual subunits, and the role of specific protein-protein
interactions. Experiments will be based on a combination of biochemical analysis, correlated light and electron
microscopy to follow tagged proteins expressed at endogenous levels, and cell fusion to detect protein
dynamics. Correlative light and electron microscopy will be used to visualize the ultrastructure of membrane
compartments decorated by tagged proteins, allowing for detailed in vivo analysis of tether function.

## Key facts

- **NIH application ID:** 9938600
- **Project number:** 5R01GM105783-06
- **Recipient organization:** UNIVERSITY OF CHICAGO
- **Principal Investigator:** AARON P TURKEWITZ
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $291,916
- **Award type:** 5
- **Project period:** 2014-05-01 → 2023-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9938600

## Citation

> US National Institutes of Health, RePORTER application 9938600, Mechanisms of tether function in endolysosomal trafficking - Renewal - Resubmission 01 (5R01GM105783-06). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9938600. Licensed CC0.

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