The membrane anchor of the transcriptional activator SREBP is characterized by intrinsic conformational flexibility

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 40; pp. 12390 - 12395
• Main Authors: Linser, Rasmus, Salvi, Nicola, Briones, Rodolfo, Rovó, Petra, de Groot, Bert L., Wagner, Gerhard
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 06-10-2015; National Acad Sciences
• Subjects: Amino Acid Sequence; Animals; Binding Sites; Biological Sciences; Cell adhesion & migration; Circular Dichroism; Humans; Life Sciences; Magnetic Resonance Spectroscopy; Membrane Lipids - chemistry; Membrane Lipids - metabolism; Membrane Proteins - chemistry; Membrane Proteins - genetics; Membrane Proteins - metabolism; Molecular Dynamics Simulation; Molecular Sequence Data; Mutation; Proteases; Protein Binding; Protein Structure, Secondary; Protein Structure, Tertiary; Proteins; Proteolysis; Sequence Homology, Amino Acid; Sterol Regulatory Element Binding Protein 1 - chemistry; Sterol Regulatory Element Binding Protein 1 - genetics; Sterol Regulatory Element Binding Protein 1 - metabolism; Transcription factors; cellular lipid homeostasis; cancer; SREBP; membrane proteins; regulated intramembrane proteolysis
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1513782112

Regulated intramembrane proteolysis (RIP) is a conserved mechanism crucial for numerous cellular processes, including signaling, transcriptional regulation, axon guidance, cell adhesion, cellular stress responses, and transmembrane protein fragment degradation. Importantly, it is relevant in various diseases including Alzheimer’s disease, cardiovascular diseases, and cancers. Even though a number of structures of different intramembrane proteases have been solved recently, fundamental questions concerning mechanistic underpinnings of RIP and therapeutic interventions remain. In particular, this includes substrate recognition, what properties render a given substrate amenable for RIP, and how the lipid environment affects the substrate cleavage. Members of the sterol regulatory element-binding protein (SREBP) family of transcription factors are critical regulators of genes involved in cholesterol/lipid homeostasis. After site-1 protease cleavage of the inactive SREBP transmembrane precursor protein, RIP of the anchor intermediate by site-2 protease generates the mature transcription factor. In this work, we have investigated the labile anchor intermediate of SREBP-1 using NMR spectroscopy. Surprisingly, NMR chemical shifts, site-resolved solvent exposure, and relaxation studies show that the cleavage site of the lipid-signaling protein intermediate bears rigid α-helical topology. An evolutionary conserved motif, by contrast, interrupts the secondary structure ∼9–10 residues C-terminal of the scissile bond and acts as an inducer of conformational flexibility within the carboxyl-terminal transmembrane region. These results are consistent with molecular dynamics simulations. Topology, stability, and site-resolved dynamics data suggest that the cleavage of the α-helical substrate in the case of RIP may be associated with a hinge motion triggered by the molecular environment.