Differential complexome profiling of CRISTA WT and KO HEK293T mitochondria

CRISTA (SMIM26) is a mitochondrial microprotein important for assembly of complex I. Here we used differential complexome profiling to study the composition of ETC complexes in SMIM26 WT and KO HEK293T mitochondria. CRISTA potentiates mitochondrial serine import via direct interactions with the serine transporter SFXN1 in the inner mitochondrial membrane. Its C-terminus furthermore interacts with the mitochondrial ribosome to form a SFXN1-CRISTA-mitoribosome triad that is enriched for mt-ND5 mRNA encoding a key enzymatic subunit of Complex I. Deletion of CRISTA reduces mitochondrial serine uptake, leading to reduced levels of folate intermediates. This in turn impairs 5-taurinomethyl(thio)uridinylation of mitochondrial tRNAs (tm5U and tm5S2U), leading to a specific loss of ND5 translation and a stall in Complex I biogenesis.