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Lecture 16

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Biology (Sci)
BIOL 201
Greg Brown

Lecture 16 Orientation of Multipass Proteins: Hydropathy profiles: a characteristic of a given polypeptide, a technique to identify hydrophobic domains. Each a.a. has a value on the hydropathy index, a measurement of the a.a’s hydrophobicity/philicity. The more positive, the more hydrophobic. To determin hydropathy, calculate average hydropathy for 5 a.a. window, slide over, calculate the new set of 5 a.a., to calculate, and thus produce a plot of the average vs. position graph of amino acid in the polypeptide. Protein Modification in the ER: Proteins fold relatively slowly when compared to covalent bond formation. Most protein that enter the ER are glycosylated, with carbohydrates attached, and many of them assemble with each other to form a multi-subunit complex. It is important to note that only the correctly folded proteins are allowed to be secreted from the ER and sent to the Golgi. Enzyme protein disulfide isomerase, which can exist in reduced form with 2 exposed sulfhydride group or oxidized, with the 2 groups linked. In its oxidized form, the enzyme will react with cysteine to form a disulfide bridge, becoming reduced in the process. Ero1 will convert reduced form PDI into oxidized PDI. Exposed protein, with PDI, will open up its disulfide bond, and form a disulfide bridge in its correct form. The glycosylation process occurs either N-linked or O-linked. N-linked bonds require a preformed oligosaccharide to attach to Asn residues of the protein. The carbohydrate is synthesized on Dolichol phosphate, which is an ER phospholipid. Tenichmycin can block this process. Only Asn residues flanked by X-s
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