# Understanding the Mechanisms of Respiratory Supercomplexes and mitochondrial Complex I

> **NIH NIH R35** · UNIVERSITY OF CALIFORNIA AT DAVIS · 2022 · $358,461

## Abstract

PROJECT SUMMARY/ABSTRACT
The mitochondrial oxidative phosphorylation electron transport chain (ETC) is composed of five large
membrane protein complexes (CI, CII, CIII2, CIV and CV) and is responsible for the production of the majority
of cellular ATP. Consequently, the ETC is essential to bioenergetic metabolism. ETC defects are one of the
most commonly diagnosed congenital metabolic defects, with CI deficiencies representing roughly a third of
these diagnoses. Although ~50% of patients with CI deficiencies die within the first 2 years of life and only
~25% reach 10 years of age, CI remains the least well mechanistically understood of all the ETC complexes.
Furthermore, despite the large medical need, there are currently no effective treatments for CI or other ETC
deficiencies. This discrepancy stems in part from an incomplete understanding of the molecular mechanisms of
the individual complexes and their higher-order assemblies into supercomplexes (SCs). In mammalian heart
mitochondria the majority of CI is found in association with CIII2 and CIV (SC I+III2+IV, the respirasome) or in
association with CIII2 (SC I+III2). Recent biochemical and structural work has produced the first atomic-
resolution structures of mammalian mitochondrial CI and defined the arrangement of the individual complexes
within the respirasome and SC I+III2. However, significant questions remain regarding the function, mechanism
and regulation of the ETC complexes and SCs. To address these gaps in our understanding and to develop
the basic science that will underpin potential treatment strategies of ETC defects, we will establish two major
research directions in my lab. Using detailed biochemical and enzymatic analyses together with single particle
cryo-electron microscopy structural characterizations, we will elucidate the mechanisms, functions and
regulation of 1) isolated CI and 2) respiratory SCs. To achieve this, we propose to perform systematic
functional and structural comparisons of respiratory CI and SCs purified from mammalian mitochondria (from
both HeLa cell culture and porcine heart tissue), the a-proteobacteria Paracoccus denitrificans and the fungal
model system Neurospora crassa. P. denitrificans is one of the closest living organisms to the ancestral a-
proteobacteria that originated mitochondria after the endosymbiotic event. N. crassa is an established,
powerful genetic and biochemical system for bioenergetics, for which nonetheless no high-resolution ETC
structures are available. Comparing the CI and SCs from these divergent and genetically tractable organisms
to their mammalian counterparts will allow us to test several key mechanistic hypotheses in the field and to
identify the conserved features of CI and SC mechanism and regulation. This will provide deep insights into the
energy-converting mechanism of CI and the physiological roles of SC formation, which will define the scientific
foundation needed for the development of therapeutic strategies ag...

## Key facts

- **NIH application ID:** 10405545
- **Project number:** 5R35GM137929-03
- **Recipient organization:** UNIVERSITY OF CALIFORNIA AT DAVIS
- **Principal Investigator:** James Anthony Letts
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $358,461
- **Award type:** 5
- **Project period:** 2020-08-01 → 2025-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10405545

## Citation

> US National Institutes of Health, RePORTER application 10405545, Understanding the Mechanisms of Respiratory Supercomplexes and mitochondrial Complex I (5R35GM137929-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10405545. Licensed CC0.

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