Moving Proteins into Membranes and Organelles PDF

1 MOVING PROTEINS INTO MEMBRANES AND ORGANELLES 10/6/2024 Tobias Weinrich, PhD School of Integrative Biological and Chemical Sciences  2 Student Learning Outcomes ▪ Outline the process of protein synthe...

1 MOVING PROTEINS INTO MEMBRANES AND ORGANELLES 10/6/2024 Tobias Weinrich, PhD School of Integrative Biological and Chemical Sciences  2 Student Learning Outcomes ▪ Outline the process of protein synthesis by free ribosomes and membrane-bound ribosomes. ▪ Identify and explain the role of signal sequences in protein sorting within the cell. ▪ Illustrate the structure of the nuclear envelope and nuclear pore complex. ▪ Summarize how proteins are transported into and out of the nucleus. ▪ Distinguish the roles of smooth and rough ER. ▪ Summarize the mechanisms that target proteins to the ER. ▪ Explain how proteins are inserted into the ER membrane. ▪ Explain the post-translational modifications and folding processes that occur in the rough ER. ▪ Describe the mechanisms of quality control in the ER and how they ensure protein functionality. ▪ Discuss the strategies used by the ER to retain resident proteins.  3 Lecture Structure 1. Introduction to compartments 5. Retention of resident ER proteins 2. Protein synthesis and sorting 2.1 Protein synthesis 2.2 Signal sequences 3. Gated transport (nuclear) 4. Endoplasmic Reticulum 4.1 Smooth Endoplasmic Reticulum A. Phospholipid synthesis B. Drug detoxification 4.2 Rough Endoplasmic Reticulum 4.2.A ER protein synthesis 4.2.B ER Protein Modifications and folding 4.2.C ER Protein Quality Control  4 1. Introduction to Compartments ▪ Internal membrane compartments – specialized function ▪ Endomembrane system ▪ Extensive communication  5 2.1 Protein synthesis ▪ Ribosomes ▪ Free ribosomes in cytosol (soluble) Different PROTEIN destination (PROTEIN TRAFFICKING) ▪ Membrane-bound ribosomes (RER) Cytosol Nucleus N-term Mitochondria Chloroplasts FREE PROTEIN F in cytosol Peroxisomes F Nuclear membrane Requires vesicular transport! Plasma membrane Golgi Endosomes Lysosomes PROTEIN in RER Lumen Extracellular proteins (secretory versicles)  6 2.1 Protein synthesis A. FREE RIBOSOMES IN CYTOSOL ▪ Initiate and complete translation in cytosol ▪ Protein destination - post-translational import (signal sequence) a. Soluble cytoplasmic proteins and peripheral membrane proteins b. Transport across membranes (translocation) – lumen or membrane of organelle ▪ Mitochondrial proteins encoded in nuclear DNA ▪ Chloroplasts proteins encoded in nuclear DNA ▪ Peroxisome proteins c. Gated transport (import into nucleus) – nuclear pores ▪ Nuclear proteins found in the nucleoplasm (e.g. histones) Mitochondria Chloroplast Nucleus  7 2.1 Protein synthesis B. MEMBRANE-BOUND RIBOSOMES (ROUGH ENDOPLASMIC RETICULUM) ▪ Initiate protein synthesis in cytosol and complete in RER – co-translational import ▪ SRP (signal recognition particle) recognizes N-term ER signal sequence ▪ Protein destination: transmembrane transport + vesicular transport ▪ Endomembrane system or secretion from the cell  8 2.2 Signal sequences direct proteins to the correct compartment ▪ Signal sequences direct proteins to the correct compartment ▪ Import into RER – rich in hydrophobic amino acids ▪ Import into nucleus – rich in positively charged amino acids (nuclear) Co-translational Post-translational Transport mechanisms  9 3. Gated transport – Nucleus NUCLEUS ▪ Genetic information – chromatin ▪ Storage, retrieval and duplication ▪ Nuclear envelope – double membrane-bound organelle – ▪ Outer membrane – continuous with ER ▪ Inner membranes – associated with nuclear lamina (lamins, intermediate filaments) ▪ Nuclear pore complex (NPC) – protein channels in/out transport ▪ Nucleoporins Nuclear Pore Complex NPC NPC  10 3. Gated transport – Nuclear Pore Complex A. SIMPLE DIFFUSION ▪ Small hydrophilic molecules (