BIOL2056 Cell Biology Lecture 4 - PDF

BIOL2056: Cell Biology Protein Targeting: Peroxisome Recommended Literature: Alberts Molecular Biology of the Cell. 6th ed. Chapter 12 Dr Triana Amen [email protected], Building 85, Room 3035 Learning objectives Peroxisomes – key players...

BIOL2056: Cell Biology Protein Targeting: Peroxisome Recommended Literature: Alberts Molecular Biology of the Cell. 6th ed. Chapter 12 Dr Triana Amen [email protected], Building 85, Room 3035 Learning objectives Peroxisomes – key players in redox homeostasis and lipid metabolism 1 Peroxisome protein import machinery and targeting signals 2 - 4 How are proteins translocated into peroxisomes? 2 Unusual protein translocation 4 3 characteristics of peroxisomal import Case study: peroxisome biogenesis disorders Recommended Literature: Alberts Molecular Biology of the Cell. 6th ed. Chapter 12 Why do cells need peroxisomal protein targeting? All eukaryotic cells Peroxisomes synthesize essential contain peroxisomes lipids (e.g. ether lipids) Light produced by luciferase in peroxisomes Peroxisomes catalyze reactions that pass electrons to oxygen producing peroxide 2 types of Peroxisome Targeting Signals - PTS The Peroxisomal Targeting Signal-1 (PTS1) is a C-terminal tripeptide that is sufficient to direct proteins into peroxisomes - [SAGCN]1-[RKH] 2- [LIVMAF] 3 PTS1 is localized at the veryPeroxisomal >sp|Q9R0H0|ACOX1_MOUSE C-terminus acyl-coenzyme A oxidase 1 MNPDL…… …PNAVALVDAFDFKDVTLGSVLGRYDGNVYENLFEWAKKSPLNKTEVHESYYKHLKPLQSKL Peroxisomal targeting signal-2 (PTS2) is an N-terminal amino acid sequence: [RK]-[LVIQ]-X-X-[LVIHQ]-[LSGAK]-X-[QH]-[LAF] PTS2 is localized close to the N-terminus >sp|O14832|PAHX_HUMAN Phytanoyl-CoA dioxygenase, peroxisomal MEQLRAAARLQIVLGHLGRPSAGAVVAHPTSGTISSAS……KDIWMFRARLVKGERTNL One PTS is sufficient to import the protein into peroxisomes. PEX5 recognizes Peroxisome Targeting Signal PTS PEX5 complex with PTS1 PEX5 is the receptor for PTS1 and PTS2* *PEX7 and PEX5 interact with PTS2 PEX5 interacts with the PTS TRP C-terminal part with PTS1 signal via a series of tetratricopeptide repeats (TPRs*) within its C-terminal half TRP are regions of repeated alpha helical 34aa motifs Gatto et al., Nature Structural Biology, 2002 PEX13 and PEX14 form translocation complex PEX13 and PEX14 are subunits of a peroxisomal protein translocation complex that wasn’t observed until 2023 PEX13/14 PEX5-Cargo complex binds PEX13/14 translocation complex to import cargo inside peroxisomes Peroxisomes can import large folded proteins Peroxisomes can import large folded proteins, protein complexes, and Cargo even particles coated with PTS PEX13/14 Peroxisomal import of gold particles 9 nm coated with PTS Carg o 0.2µm Walton et al., 1995 Peroxisomal import: how it works? Gao et al., 2023, Science Ravindran et al., 2023, Nature PEX13/14 Peroxisomes import large folded proteins and protein complexes -> there must be a large pore complex that was never observed Unless it is transient? PEX13 has YG repeats (like FG repeats of the Nups in NPCs that promote nuclear import!) 3 models of peroxisomal import: NPC- like! Proteins are produced in the cytoplasm* *mitochondria and chloroplast produce small number of proteins Diffusion between compartments is limited Proteins half life is.. A cohesive YG rich domain of PEX13 forms a meshwork promoting PEX5-Cargo diffusion Models of peroxisomal import: condensation PEX5-cargo complex interacts with YG repeats of PEX13 inducing its clustering YG repeats create a mesh like structure that helps import cargo bound to PEX5 inside peroxisomes PEX5 receptor is exported through PEX2-10-12 complex PEX5 binds Cargo that contains PTS PEX5-Cargo complex interacts with YG repeats of PEX13 (Fig.B) and passes into peroxisomes Cargo dissociates; PEX5 is recycled in an unfolded state back to the cytoplasm Peroxisomal import does not require energy Peroxisomal import does not require energy! PEX5 recycling requires energy of ATP through PEX1/PEX6 ATPase  Protein targeting into peroxisomes Targeting Receptor Transport Energy Protein Stage Signal Complex State Targeting pathway C-terminal PEX5 PEX13/PEX14 No Folded Post- PTS1 or N- translational terminal PTS2  Peroxisomes in brain development Loss of PEX5 leads to an impaired peroxisomal import and a complete loss of peroxisomal functions – Peroxisome Biogenesis Disorder (PBD) The Zellweger spectrum of peroxisome biogenesis disorders (PBD) are autosomal recessive disorders characterized by neurological defects, that include demyelination Powers and Moser, 1998, Brain Pathology What if a protein has both PTS and MLS? Proteins can be localized to two or more different compartments through multiple targeting signals Yeast phosphatase Ptc5 has an N-terminal mitochondrial localization sequence and C-terminal peroxisomal targeting sequence 1 (PTS1) Stehlik et al., 2020 Can a protein without a targeting sequence be imported? Proteins can enter peroxisomes through interaction with other peroxisomal cargoes – piggy backing Malate dehydrogenase Mdh2 enters peroxisomes though Mdh3 interaction (Mdh3 has a PTS1) Gabay-Maskit et al., 2020 Summary Peroxisome Targeting Sequence (PTS) – containing cargo protein is 1 recognized by PEX5 and imported into peroxisomes 2 PEX5 receptor guides proteins to - 4 2 the peroxisomes 4 3 PEX13 and PEX14 transport PEX5- Cargo complex inside peroxisomes Proteins can be in multiple locations inside the cell Recommended literature and open questions Where do I learn more about this? Recommended Literature: Alberts Molecular Biology of the Cell. 6th ed. Chapter 12 Protein import into peroxisomes occurs through a nuclear pore–like phase, 10.1126/science.adf3971 Peroxisome biogenesis initiated by protein phase separation, 10.1038/s41586-023-06044-1 Interesting reads: Peroxisomal targeting of a protein phosphatase type 2C via mitochondrial transit, 10.1038/s41467-020-16146-3 A piggybacking mechanism enables peroxisomal localization of the glyoxylate cycle enzyme Mdh2 in yeast, 10.1242/jcs.244376 Import of stably folded proteins into peroxisomes, 10.1091/mbc.6.6.675 Questions to think about: How can a protein change its localization to a different compartment? What is a piggy backing mechanism of protein translocation? Terminology: Peroxisome, Peroxisome Targeting Sequence (PTS), PTS1, PTS2, PEX5, PEX13/PEX14, peroxisomal protein import