3. (6pts each) Suppose the following GTPases are mutated so that they permanentl

Question

3. (6pts each) Suppose the following GTPases are mutated so that they permanently bind to GDP. Please predict the location where the stated cargo proteins would accumulate, and provide a brief explanation (2 sentences max). A. GTPase: Ran, Cargo: Protein with NLS sequence Cargo protein location with mutant Ran- Explanation- B. GTPase: Sar1, Cargo: Secreted protein Cargo protein location with mutant Sar Explanation - C. GTPase: Dynamin, Cargo: Low Density Lipoprotein (LDL) particle Cargo protein location with mutant dynamin - Explanation - D. GTPase: ARF1, Cargo: ER Resident protein with KDEL sequence Cargo protein location with mutant ARF1 Explanation

Explanation / Answer

A).Proteins that must be imported to nucleus from the cytoplasm carry nuclear localization signals.(NLS) that are bound by importins .A (NLS) is a sequence of aminoacids that act as a tag.Proteins transfer RNA,& assembled ribosomal subunits are exported from nucleus due to association with exportins which bind signaling sequence (NES).The ability of both importins & exportins to transport their cargo i s regulated by small Ras related GTPase,Ran.B).Secretory proteins are efficiently stored at high concentration in zymogen granules by steps that sequentially enrich proteins several hundred fold over that found ER lumen29,30.Cargo selection & export from the endoplasmic reticulum is mediated by COPII coat that includes the small GTPase Sar1&Sec23/24& sec13/31.The sequential events regulsted by purified Sar1& COPII coat complexes during synchronized export of cargo from the ER in vitro.C).In clathrin mediated endocytosis specificity & selectivity for cargoes are thought to be tightly regulated by cargo specific adaptors for distinct cellular functions.actin binding protein girdin is a regulator of cargo selective CME. Girdin interact with dynamin2 that excises endocytic vesicles from plasma membrane,& functions as GTPase activating protein.D).ARF1 GTP binds to golgi membranes and recruits coatomer.A golgi localized ARFGAP is necessary for ARF1 function cargo protein will need to interact with some of these components to be efficiently sorted into budding COPI coated vesicles or tubuler structures.this should apply particular to ligand occupiedKDEL receptor ERD2 stimulate its rapid transport of cisGolgi.hence KDEL cargo protein s can regulate tbeir own sorting & transport.

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