*Article* **Mutations in** *NDUFS1* **Cause MetabolicReprogramming and Disruption of theElectronTransfer**

#### **Yang Ni 1,2,3, Muhammad A. Hagras 4,5, Vassiliki Konstantopoulou 6, Johannes A. Mayr 7, Alexei A. Stuchebrukhov 4 and David Meierhofer 1,\***


Received: 24 July 2019; Accepted: 20 September 2019; Published: 25 September 2019

**Abstract:** Complex I (CI) is the first enzyme of the mitochondrial respiratory chain and couples the electron transfer with proton pumping. Mutations in genes encoding CI subunits can frequently cause inborn metabolic errors. We applied proteome and metabolome profiling of patient-derived cells harboring pathogenic mutations in two distinct CI genes to elucidate underlying pathomechanisms on the molecular level. Our results indicated that the electron transfer within CI was interrupted in both patients by di fferent mechanisms. We showed that the biallelic mutations in *NDUFS1* led to a decreased stability of the entire N-module of CI and disrupted the electron transfer between two iron–sulfur clusters. Strikingly interesting and in contrast to the proteome, metabolome profiling illustrated that the pattern of dysregulated metabolites was almost identical in both patients, such as the inhibitory feedback on the TCA cycle and altered glutathione levels, indicative for reactive oxygen species (ROS) stress. Our findings deciphered pathological mechanisms of CI deficiency to better understand inborn metabolic errors.

**Keywords:** complex I (CI) deficiency; metabolome and proteome profiling; reactive oxygen species (ROS); respirasome assembly; electron tunneling (ET)
