An Inner Mitochondrial Membrane Microprotein from the SLC35A4 Upstream ORF Regulates Cellular Metabolism.

Area of Science:

• Molecular Biology
• Cellular Metabolism
• Gene Regulation

Background:

• Upstream open reading frames (uORFs) are cis-acting regulatory elements found in ~50% of human and mouse transcripts.
• Historically, microproteins encoded by uORFs were overlooked due to the dogma of single protein production per mRNA.
• uORFs can regulate downstream open reading frame (ORF) translation, particularly under stress conditions.

Purpose of the Study:

• To investigate the hypothesis that a conserved uORF in SLC35A4 mRNA encodes a functional microprotein.
• To characterize the function and localization of the putative microprotein derived from the SLC35A4 uORF.

Main Methods:

• Computational and empirical identification of uORFs.
• Biochemical and cellular experiments to analyze microprotein production and function.
• Loss-of-function studies to assess the impact on cellular respiration.

Main Results:

• Identification of a 103-amino acid microprotein, SLC35A4-MP, encoded by a conserved uORF in SLC35A4 mRNA.
• SLC35A4-MP localizes to the inner mitochondrial membrane (IMM).
• Loss of SLC35A4-MP function significantly impairs maximal cellular respiration, highlighting its role in metabolism.

Conclusions:

• SLC35A4-MP is a functional microprotein vital for cellular respiration and ATP generation.
• Conserved uORFs represent a significant, largely untapped source of functional microproteins.
• These findings expand the known repertoire of functional microproteins and their roles in cellular processes.