Translocation of MHC I molecule to the cytosol! - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 12-27-2011
USMLE Forums Veteran
 
Steps History: Not yet
Posts: 281
Threads: 74
Thanked 131 Times in 68 Posts
Reputation: 141
Immunology Translocation of MHC I molecule to the cytosol!

During an experiment the US 11 gene product of the CMV is expressed constitutevely after stable transinfection in tumor cell line. its found that the gene product causes translocation of class I MHC molecules from ER to the cytosol. Which of the following is the most likely to happen to the class I MHC?

a. Association with invariant chain
b. binding of peptides with endocytic pathway
c. degradation of proteosomes
d. formation of MHC class I /II hybrid molecules
e. interaction with T cell receptor
Reply With Quote Quick reply to this message



  #2  
Old 12-27-2011
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 851
Threads: 88
Thanked 710 Times in 380 Posts
Reputation: 720
Default

e.

coz virally infected cell presents its antigen on MHC class I which is recognized by TCR (T cell receptor) of Cytotoxic T cell CD8+ which then gets activated.
Reply With Quote Quick reply to this message
  #3  
Old 12-27-2011
USMLE Forums Scout
 
Steps History: 1 + CK
Posts: 99
Threads: 8
Thanked 33 Times in 29 Posts
Reputation: 43
Default

http://upload.wikimedia.org/wikipedi...processing.svg
Reply With Quote Quick reply to this message
 
  #4  
Old 12-27-2011
USMLE Forums Newbie
 
Steps History: Not yet
Posts: 4
Threads: 2
Thanked 0 Times in 0 Posts
Reputation: 10
Default

In normal antigen processing, yes, the MHC1 class molecule (in conjunction with the antigen) would localize to the outer cytoplasmic membrane for interaction with the T cell receptor.
However, I think that if the MHC1 molecule ended up naked in the cytosol (not inside a secretory vesicle), it would be digested by proteasomes. If you re-read the question, does answer choice C state " Degradation BY proteasomes"?
This would make sense as a CMV gene/protein would likely want to ESCAPE antigen presentation (and thus detection) via causing MHC1 degradation in the cytosol and not facilitate its translocation to the membrane.

Note: The above info is an educated guess. Please double check.
Reply With Quote Quick reply to this message
  #5  
Old 12-29-2011
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 851
Threads: 88
Thanked 710 Times in 380 Posts
Reputation: 720
Default

@ indigo

could u pls tell the answer to this question
Reply With Quote Quick reply to this message
  #6  
Old 12-29-2011
dhanush's Avatar
USMLE Forums Scout
 
Steps History: Step 1 Only
Posts: 35
Threads: 4
Thanked 56 Times in 18 Posts
Reputation: 66
Default

MHC class molecules r suppose to bind to intra cellular peptides n then translocate to the surfece of the cell to work properly..
in tis infected cell it is rather pumped out of ER into cytosol..
tis probably has happened due to defective post translational modification or due to the mutation in the coding gene,,
all the defective proteins in the cell r marked by ubiqitin to be later degraded in the proteosomes..so its C.. degraded in the proteosomes
Reply With Quote Quick reply to this message
  #7  
Old 12-29-2011
USMLE Forums Veteran
 
Steps History: Not yet
Posts: 281
Threads: 74
Thanked 131 Times in 68 Posts
Reputation: 141
Default

Ans is proteosome degradation
Reply With Quote Quick reply to this message
The above post was thanked by:
drortho (01-17-2012), jinni (12-30-2011)
  #8  
Old 02-11-2012
USMLE Forums Scout
 
Steps History: Not yet
Posts: 96
Threads: 15
Thanked 19 Times in 18 Posts
Reputation: 29
Default

can someone please explain this answer
thank you
Reply With Quote Quick reply to this message
  #9  
Old 02-18-2012
USMLE Forums Veteran
 
Steps History: Step 1 Only
Posts: 216
Threads: 23
Thanked 180 Times in 72 Posts
Reputation: 190
Default C

Quote:
Originally Posted by philios View Post
In normal antigen processing, yes, the MHC1 class molecule (in conjunction with the antigen) would localize to the outer cytoplasmic membrane for interaction with the T cell receptor.
However, I think that if the MHC1 molecule ended up naked in the cytosol (not inside a secretory vesicle), it would be digested by proteasomes. If you re-read the question, does answer choice C state " Degradation BY proteasomes"?
This would make sense as a CMV gene/protein would likely want to ESCAPE antigen presentation (and thus detection) via causing MHC1 degradation in the cytosol and not facilitate its translocation to the membrane.

Note: The above info is an educated guess. Please double check.
You're absolutely right there. And you picked up the typo correct too. (Proteasomes are meant to lyse proteins, not be lysed by proteins!)

The whole process gets clear by an image uploaded by someone -
http://upload.wikimedia.org/wikipedi...processing.svg

The brief steps are -
  • Processing of the foreign "antigen" (eg. a viral protein) in the cytosol by the proteasome.
  • The resulting 'peptide fragment' (immunologically called: epitope) is then transfered from the cytosol into the endoplasmic reticulum, where it gets loaded on the MHC -I molecule.
  • Finally, the loaded MHC molecule is transfered to the Golgi system and finally carried away by vesicles budding off from the Golgi.
  • These vesicles are destined to dock on the cell membrane where the MHC I interacts with TCR and the "epitope" is presented for recognition of cytotoxic T cells (CD8 +ve).

But this is how it occurs normally. Now coming back to the question. Some hypothetical protein is forcing the "naked" MHC I molecules (very well framed by Philios) to enter the cytosol. They aren't supposed to do that and shall supposedly be degraded by the proteasome system (I guess that's what it normally does).

Hope that helped.
Reply With Quote Quick reply to this message
The above post was thanked by:
mohitkmc (02-18-2012)



Reply

Tags
Immunology-, Microbiology-, Molecular-Biology-, Step-1-Questions

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
32 ATPs per glucose molecule? level1 USMLE Step 1 Forum 7 04-07-2012 09:37 AM
Which molecule is responsible for rapid collapse of microtubules? ricko335 USMLE Step 1 Forum 3 11-01-2011 05:33 PM
How many ATPs per Glucose Molecule soulhead USMLE Step 1 Forum 4 12-07-2010 07:11 PM
Lymphoma Translocation! khushboo USMLE Step 1 Forum 3 05-24-2010 08:50 AM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)