Mitochondrial peptide BRAWNIN is essential for vertebrate respiratory complex III assembly
Shan Zhang, Boris Reljić, Chao Liang, Baptiste Kerouanton, Joel Celio Francisco, Jih Hou Peh, Camille Mary, N. Suhas Jagannathan, Volodimir Olexiouk, Claire Tang, Gio Fidelito, Srikanth Nama, Ruey‐Kuang Cheng, Caroline Lei Wee, Loo Chien Wang, Paula Duek, Prabha Sampath, Lydie Lane, Enrico Petretto, Radoslaw M. Sobota, Suresh Jesuthasan, Lisa Tucker‐Kellogg, Bruno Reversade, Gerben Menschaert, Lei Sun, David A. Stroud, Lena Ho
Abstract
The emergence of small open reading frame (sORF)-encoded peptides (SEPs) is rapidly expanding the known proteome at the lower end of the size distribution. Here, we show that the mitochondrial proteome, particularly the respiratory chain, is enriched for small proteins. Using a prediction and validation pipeline for SEPs, we report the discovery of 16 endogenous nuclear encoded, mitochondrial-localized SEPs (mito-SEPs). Through functional prediction, proteomics, metabolomics and metabolic flux modeling, we demonstrate that BRAWNIN, a 71 a.a. peptide encoded by C12orf73, is essential for respiratory chain complex III (CIII) assembly. In human cells, BRAWNIN is induced by the energy-sensing AMPK pathway, and its depletion impairs mitochondrial ATP production. In zebrafish, Brawnin deletion causes complete CIII loss, resulting in severe growth retardation, lactic acidosis and early death. Our findings demonstrate that BRAWNIN is essential for vertebrate oxidative phosphorylation. We propose that mito-SEPs are an untapped resource for essential regulators of oxidative metabolism.