Sorting and sorting and regulation of intracellular transport
- 1. Sorting and Regulation of Intracellular Transport SUBMITTED TO – MRS. ALKA SUBMITTED BY – LASHIKA CELL AND MOLECULAR BIOLOGY CENTRE OF BIOINFORMATICS 2116 1
- 2. Introduction It is the movement of the solutes and the vesicles within the cell Eukaryotic cells transport packets of components (membrane-bound vesicles and organelles, proteins rafts, mRNA, chromosomes) Mechanism of movement is the attachment to molecular motors that haul them along microtubules and actin filaments. This is distinct from intracellular transport, which deals solely with the movement of cargo between cells not the net movement within a cell Intracellular transport involves the movement of various components within the cells Paracellular transport refers to the transfer of substances across an epithelium by passing though the intercellular space between the cells transcellular transport , where the substances travel through the cell, passing though both the apical membrane and basolateral membrane. 2
- 3. The cytoskeleton is key in intracellular transport as they provide the mechanical support necessary for movement Composed of actin , intermediate filaments and microtubules which mediate locomotion, intracellular transport of organelles, cell shape and chromosome separation. Intracellular transport is unique to eukaryotic cells as they possess organelles enclosed in membranes Conversely, in prokaryotic cells there is no need for this specialized transport mechanism as there are no membranous organelles and compartments to traffic between ( simple diffusion) 3
- 4. Protein sorting The process by which the proteins are transported to their appropriate target in the cell or outside it Proteins can be targeted to the inner space of an organelle , different intracellular membranes, plasma membrane, or to exterior of the cell via secretion Many proteins carry the signals that target them to their destinations The signals are the fundamental component of the sorting system Sorting decision made early in the process of biosynthesis 4
- 5. Targeting sequence or compound Organelle targeted Signal peptide sequence Membrane of ER Amino terminal KDEL sequence Luminal surface of ER Amino terminal sequence( 70 residue region) Mitochondria NLS ( Egg. Pro – lys – ala- lys- val) Nucleus PTS (Eg: ser- lys- leu) Peroxisome Mannose 6 phosphate Lysosome 5
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- 7. Protein translocation Proteins moving from the cytosol the ER, mitochondria, chloroplasts, or peroxisomes Protein movement is mediated by specialized proteins termed protein translocators Unlike passage though nuclear pores, translocation requires unfolding or co- translational transport 7
- 8. Protein translocation into the ER Translocation of the protein into the ER is mainly guided by the signal hypothesis. It was proposed by the Bolbel and Sabatini Protein synthesized on the membrane bound polyribosomes contained a peptide extension called signal peptide Responsible for mediating their attachment with the ER membrane In contrast protein being synthesized on the free polyribosomes lack this signal peptide 8
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- 10. Mitochondrial protein import Most mitochondrial proteins are synthesized on cytoplasmic ribosomes and are post- translationally imported into this organelle. Because of the double membrane surrounding this organelle, there are four targets for mitochondrial proteins: 1. Outer membrane 3. Inner membrane 2. Intermembrane space 4. Matrix space Mitochondrial proteins usually contain an N- terminal targeting sequence that is capable of forming an amphipathic α- helix. Positively- charged residue are clustered on one side of the helix and uncharged residues are presented on the other. The mitochondrial outer membrane contains specific receptor proteins that bind to the mitochondrial targeting signal. 10
- 11. Translocation into mitochondrial matrix requires both ATP hydrolysis and an electrochemical gradient across the inner mitochondrial membrane Translocation occur at sites where the inner and outer membrane are in close apposition, these regions are known as contact sites. Proteins are imported into the mitochondria in an unfolded state. Maintenance in an unfolded state is mediated by hsp70 protein that act as molecular chaperones. Protein transport into the inner membrane or intermembrane space 11
- 12. Protein import into mitochondria: 12
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- 15. Vesicular transport Vesicular transport is predominant mechanism for exchange of proteins and lipids between membrane bound organelles in eukaryotic cells His form of transport involves the movement of various elements with the aid of bubble like vesicles created from the cell membrane It is fundamentally divided into endocytosis and exocytosis Endocytosis is divided into 3 distinct mechanism: 1. phagocytosis 2. pinocytosis 3. receptor mediated endocytosis 15
- 16. Stages of endocytosis: 16
- 17. Receptor mediated endocytosis The major mechanism of vesicular transport between ER and Golgi and also from trans Golgi to the polyribosomes takes places in the regions of the membranes known as coated pits The coated pits has high concentration of protein clarthrin and this mechanism of receptor mediated endocytosis is the clarthin coated vesicle method However there is another method in which the receptor mediated endocytosis takes place without the clarthin coated vesicles Types of coated vesicles has been distinguished 1. Clarthin coated vesicles: trans Golgi prelysosomes and from plasma membrane to endosomes 2. CPOI: Bi- directional transport from ER to golgi and in the reverse 3. COPII: from er to golgi 17
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- 19. Clathrin independent pathway The pathway proposed by Rothman and colleagues The pathway plays the major role in the anterograde transport of protein into the lysosome or the cell membrane from the ER Each transport vesicles bears one specific target marker consisted of one and more V- SNARE PROTEINS each target membrane bears T – SNARRE PROTEINS with which the V- SNARE proteins interact specifically 19
- 20. Steps of Clathrin independent transport pathway Coating coat assembly Recruitment coat proteins Bud pinching off Coat disassembly Vesicle targeting Fusion 20
- 21. Disorders related to intracellular transport Familial hypercholesteremia- Familial hypercholesterolemia, FH(type II hyperlipoproteinemia) is an autosomal dominant disorder. Results from mutation affecting the structure and function of the cell-surface receptor that binds plasma LDLs (low density lipoproteins) removing them from the circulation. The defects in LDL- receptor (LDLR) interaction result in lifelong evaluation of LDL- cholesterol in the blood. 21
- 22. 1. Receptor null mutation (lack of receptor synthesis in the ER. 2. Defective intracellular transport to golgi apparatus. 3. Defective extracellular ligand binding. 4. Defective endocytosis. 5. Failure to release LDL molecules inside the endosome 22
- 23. Another finding underlying autosomal dominant 23
- 24. Mind map: 24
- 25. REFERENCES: Harper’s illustrated biochemistry 26th edition. Rink J, Ghigo E, Kalaidzidis Y, et al. Rab conversion as a mechanism of progression from early to late endosomes. Cell. 2005:122(5):735-49. Prydz K, Dick G, Tveit H. How many ways through the Golgi maxe Traffic. Mostov KE, Verges M. Altschuler Y. Membrane traffic in polarized epithelial cells. Curr Opin Cell Biol. 2000;12(4):483-90. www.ncbi.nlm.nih.gov THANK YOU 25