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Molekularbiologie (Fach) / Soting folding (Lektion)
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- 191. Explain roughly how Hsp70 chaperones work? In the absence of Hsp70 hydrophobic patches of amino acids aggregate. Trapping the protein in a incorrect conformation or allowing to aggregate with other proteins in the cell. Stretches of amino acids bind to a peptide binding groove on Hsp70 àAggregation is prevented.
- 192. Explain how GroEL/ES chaperones work? Conformational changes occur within GroEL leading to a switch from hydrophobic to hydrophilic likely helping in folding the subtrate(SP) to refold.
- 193. What is PDI? Protein disulphide isomerase. It makes new disulphide bonds and swaps them.
- 194. In which diseases prions seems to play a role? BSE, Scrapie, GSS
- 195. Are prions only occur in higher organism? No, they accure in yeast too.
- 196. Can you cure certain prions? And if yes how? Some yeast prions can be cured by Chaperons or Co-chaperons.
- 197. What are inteins and their application in biotech? Inteins are part of proteins, that are removed. They catalyse their own removal and ligate the flanking pieces (exeins). Result is two proteins, inteins and exeins. Intein act as a mobile genetic element and move its own sequence around the genome. In Biotechnology they can be used for chemical semisynthesis (Adding an “unnatural” chemically synthesized part to a naturally produced peptide).
- 198. Three main types of lipid modification. § Acetylation by fatty acyl groups § Prenylation by isoprenoid groups § Addition of GPI anchors (glycosylphosphatidylinositol)
- 199. What is interesting about hedgehog? · is involved in developmental patterning · catalyzes self-processive reactions · only in metazoan · They are related to inteins. · Modified with cholesterol, befor it can perform his function
- 200. If you add carbohydrates to proteins how does this often effect these? o Carbohydrates are hydrophilic, so are usually on the outside of the molecule, increasing the solubility o Inappropriate protein aggregation is prevented o Protect secreted proteins from degradation and non-specific interactions o Binding sites on cell surface for recognition
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- 201. What can ROS and NOS lead to? ROS: In stress situation there is an increase in ROS and they can react with AA and cause damage. Cysteine and Methionin can be oxidized at the sulphur atom. NOS: Nitrogen species. · Cysteine can be modified by nitric oxide · Tyrosine can be O-nitraed.
- 202. Depict the UBQ pathway! 1.In ubiquitin activation, ubiquitin becomes attached to a cysteine in the active site of ubiquitin activation enzyme (E1). Most eukaryotes have a single E1. 2.E1-ubiquitin then transfers ubiquitin to a cysteine in ubiquitin conjugating enzyme (E2). There are several E2 enzymes. 3.Ubiquitin protein ligase (E3) catalyzes transfer of ubiquitin from E2-ubiquitin to the amino group of a lysine side chain of the target protein.
- 203. Looking at the UBQ pathway, how many isoforms do you have of the respective enzymes? E1: one E2: several E3: many
- 204. If you attach polyubq via K48 what does it lead to? It leads to protein degradation.
- 205. What does the proteasome do? An eukaryotic proteolytic complex, made up of ca. 30 polypetides. It degrades some ubq marked proteins
- 206. Explain one unfolded protein response (ATF6) in eukaryotes? Cells sense unfolded proteins in the endoplasmic reticulum via IRE1, PERK and ATF6 • Normally, BiP is bound to ATF6 and ATF6 resides in the ER hindering trafficking into the golgi • In conditions of stress, unfolded proteins are present and BiP binds to them preferentially, ATF6 (and CREBH) are released and in the golgi ATF6 is cleaved • This release of BiP activates ATF6, which stimulates transcriptional and translational changes that respond to the difficult conditions
- 207. Explain one unfolded protein response (sigmeE) in prokaryotes? · Cellular stress increases ànumber of badly folded proteins. · cell responds by decreasing overall protein production and/or increases chaperone and degradative activity. A bacterial example is the σE pathway. · Normally σE is bound to RseA which is found in the membrane and binds to unfolded proteins in the periplasm. · A proteolytic cascade results in release of σE which activates transcription, including that of proteases that degrade unfolded proteins. ·
- 208. Explain how proteins get imported into the ER via the SRP? · SRP (signal recognition particle). · The SRP (signal recognition particle) contains six protein subunits and one 7S RNA molecule · The signal binding site is a hydrophobic pocket allowing the SRP to recognize a lot of different sequences · Usually there are 8-9 non-polar amino acids in the signal sequence · Upon binding of the SRP to the nascent signalling sequence, protein synthesis is halted. · The SRP-ribosome complex then binds to the SRP receptor (an integral membrane complex) · • This brings the SRP-ribosome close to a protein translocator (whose core is called Sec61) · SRP and SRP-receptor are released and the translocator transfers the growing chain through the membrane · When the translocated protein grows long enough a signal peptidase cleaves off the signal sequence. The signal sequence is released into the lipid bilayer where it is rapidly degraded
- 209. What is the SRP composed of? six protein subunits and one 7S RNA molecule
- 210. How are proteins brought into/out of the nucleus? • Transport in and out of the nucleus is highly-regulated and travel is via nuclear pore complexes (NPCs) • NPCs are rich in positive amino acids, and are recognized by nuclear import receptors, which bind to parts of the NPC · Import/export into/from the nucleus relies on short signalling sequences. · Import relies on nuclear import receptors and in addition some proteins might need adapter sequences. · Nuclear export works like the nuclear import. Only now nuclear export receptors are needed. In short: Importins/Exportins
- 211. How do importins/exportins "know" when to release their cargo? Cargo proteins containing a nuclear localization signal (NLS) are bound by importins and transported into the nucleus. Inside the nucleus, RanGTP binds to importin and releases the import cargo. Cargo that needs to get out of the nucleus into the cytoplasm binds to exportin in a ternary complex with RanGTP. Upon hydrolysis of RanGTP to RanGDP outside the nucleus, the complex dissociates and export cargo is released..
- 212. Why can import into chlorplast/mitos complex? Import into chloroplasts and mitochondria/chloroplasts can need multiple sequences depending on the exact destination. Multiple compartments have to be targeted. Mitochondria have TOM / TIM complexes (translocase outer / inner mito membrane). Chloroplasts have TOC / TIC complexes (transport outer / inner envelope chloro)