Question

PLEASE ANSWER ALL THE QUESTIONS IN EACH PART

Suppose the following proteins are mutated with the described molecular effects. Please predict the cellular location where the stated cargo proteins would accumulate, and provide a brief explanation.

A. importin is mutated so it is permanently bound to Ran-GDP Cargo: Protein with NLS sequence (i) Cargo protein location with mutant Importin - (ii) Explanation

B. Exportin is mutated so it is permanently bound to Ran-GDP Cargo: Protein with NES sequence (i) Cargo protein location with mutant Importin - (ii) Explanation

C. ARF1 is mutated so it is unable to hydrolyze GTP Cargo: Protein with KDEL (ER Retrieval) signal (i) Cargo protein location with mutant ARF1 (ii) Explanation

D. Cargo: ER cargo proteins are mutated to carry a mitochondrial signal at the C-terminus (i) Mutated cargo protein location - (ii) Explanation

Answer 1

A. i) cargo will be remained in the cytoplasm.

ii) Ran cycle is associated with nuclear transport of cargoes. Ran when bound with GDP is destined to cytoplasm but in GTP bound state move inside nucleus of nuclear localization sequence (NLS) IS present.

B. i) in nucleus

ii) though the protein contain nuclear export sequence exportin is mutated, so Ran is permanently bound to GTP. So it can not move to cytoplasm.

C. i) COP coated vesicle.

ii) arf1 helps in cop1 mediated retrograde transport. Hydrolysis of arf 1 bound GTP trigger dis assembly of cop proteins. As result cargo with KDEL sequence move from Golgi to ER . if GTP can not be hydrolyzed cargoes will remain in the vesicle.

D. i) ER

ii) the sequence is generated in C terminal and the N terminal contain normal ER targeting sequence. Trafficking is determined by N terminal sequence and not by C terminal. So, proteins will be destined to ER.