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Transcript
Previously Bio308 Hypotheses for molecular basis of bipolar disorder •Suggest problem lies in protein targeting Proteins made in cytosol (cytosolic and membrane ones) Sorting places proteins in membrane and in lumen of organelles ‘Routing’ controlled by the presence or absence of targeting Information in the primary structure (the amino acid sequence) of the protein itself But first: what type of transport (general class and specific type) is used to get neurotransmitters into synaptic vesicles? Targeting to the ER If targeted to the ER where can a protein end up? Main point of entry into the endomembrane system TWO methods of targeting to ER Minor pathway: Sec-dependent translocation Identified first in bacterial genetic screens Post translational Post-translational translocation Sec- dependent Co-translational translocation Major pathway: SRP-dependent translocation First identified in in vitro experiments using canine microsomes and wheat germ translation systems Co-translational CBI 12.3 Co-translational translocation Important components from ER: SRP- receptor, TRAM Sec61 complex (& BiP/Kar2-- sometimes) Mammals: ER translocation involves “push” Yeast: ER translocation involves “push” and “pull” So the protein can now be in the ER-*Where in the ER and then what happens? ER proteins ER Where can a protein end up in the ER? How does it get there? Lumenal proteins Single transmembrane span proteins Multipass transmembrane proteins What category do our neurotransmitter and neurotransmitter receptor fall in? Getting out of the ER Golgi enzyme involved in glycosylation Neurotransmitter receptor ER Lysosomal acid hydrolase Now what? Vesicular traffic Secretory pathway: also method for delivering new PM proteins ER to Golgi to trans-Golgi network then constitutive or regulated exocytosis Constitutive and Regulated Exocytosis Constitutive= constant, sometimes called ‘bulk flow’ Constitutive does not mean ‘un-regulated’ Regulated= needs additional signal to initiate fusion of vesicle with PM