Gene7-08

Chapter 8
Protein localization
8.1 Introduction 8.2 Chaperones may be required for protein folding 8.3 Post-translational membrane insertion depends on leader sequences 8.4 A hierarchy of sequences determines location within organelles 8.5 Signal sequences initiate translocation 8.6 How do proteins enter and leave membranes? 8.7 Anchor signals are needed for membrane residence 8.8 Bacteria use both co-translational and post-translational translocation 8.9 Pores are used for nuclear ingress and egress 8.10 Protein degradation by proteasomes
8.5 Post-translational membrane insertion depends on leader sequences
Figure 8.15 Tim9-10 takes proteins from TOM to either TIM complex, and Tim813 takes proteins to Tim22-54.
8.2 Chaperones may be required for protein folding
Figure 8.4 A protein is constrained to a narrow passage as it crosses a membrane.
8.2 Chaperones may be required for protein folding
Figure 8.5 Chaperone families have eukaryotic and bacterial counterparts (named in parentheses).
8.3 The Hsp70 family is ubiquitous
Figure 8.6 DnaJ assists the binding of DnaK (Hsp70), which assists the folding of nascent proteins. ATP hydrolysis drives conformational change. GrpE displaces the ADP; this causes the chaperones to be released. Multiple cycles of association and dissociation may occur during the folding of a substrate protein.
8.6 A hierarchy of sequences determines location within organelles
Figure 8.18 The leader of yeast cytochrome c1 contains an N-terminal region that targets the protein to the mitochondrion, followed by a region that targets the (cleaved) protein to the inner membrane. The leader is removed by two cleavage events.
8.4 Hsp60/GroEL forms an oligomeric ring structure
Figure 8.7-2 GroEL forms an oligomer of two rings, each comprising a hollow cylinder made of 7 subunits.
8.5 Post-translational membrane insertion depends on leader sequences
Figure 8.12 The leader sequence of yeast cytochrome c oxidase subunit IV consists of 25 neutral and basic amino acids. The first 12 amino acids are sufficient to transport any attached polypeptide into the mitochondrial matrix.
8.1 Introduction
Figure 8.2 Proteins synthesized on free ribosomes in the cytosol are directed after their release to specific destinations by short signal motifs.
8.1 Introduction
Leader of a protein is a short N-terminal sequence responsible for passage into or through a membrane.
8.1 Introduction
Figure 8.1 Overview: proteins that are localized post-translationally are released into the cytosol after synthesis on free ribosomes. Some have signals for targeting to organelles such as the nucleus or mitochondria. Proteins that are localized cotranslationally associate with the ER membrane during synthesis, so their ribosomes are "membranebound". The proteins pass into the endoplasmic reticulum, along to the Golgi, and then through the plasma membrane, unless they have signals that cause retention at one of the steps on the pathway. They may also be directed to other organelles, such as endosomes or lysosomes.
8.5 Post-translational membrane insertion depends on leader sequences
Figure 8.10 Leader sequences allow proteins to recognize mitochondrial or chloroplast surfaces by a post-translational process.
8.6 A hierarchy of sequences determines location within organelles
Figure 8.17 Mitochondria have receptors for protein transport in the outer and inner membranes. Recognition at the outer membrane may lead to transport through both receptors into the matrix, where the leader is cleaved. If it has a membrane-targeting signal, it may be reexported.
8.4 Hsp60/GroEL forms an oligomeric ring structure
Figure 8.8 Two rings of GroEL associate back to back to form a hollow cylinder. GroES forms a dome that covers the central cavity on one side. Protein substrates bind to the cavity in the distal ring.
8.4 Hsp60/GroEL forms an oligomeric ring structure
Figure 8.7-1 A protein may be sequestered within a controlled environment for folding or degradation.
8.4 Hsp60/GroEL forms an oligomeric ring structure
Figure 8.9 Protein folding occurs in the proximal GroEL ring and requires ATP. Release of substrate and GroES requires ATP hydrolysis in the distal ring.
8.5 Post-translational membrane insertion depends on leader sequences