mTOR Flashcards
What type of science is the mTOR pathology
BOTTOM UP
What is mTOR
known as a master regulator of cell signalling. the mechanistic target of rapamycin
name some properties of rapamycin
antifungal
antitumour
immunosuppressant
what does mTOR bind to to form a a gain of function complex
FKB12 (enzyme)
what is FKB12
peptidyl-prolyl isomerase enzyme
true or false mTOR has a highly conserved structure
true as it serves a very important function
describe the structure of mTOR
20 heat repeats,2α linked by short loop
-FAT
-FRB
-Kianase NRD
-FACTC
what is the function of the heat repeats?
bind to other proteins
what is the function of the FAT region
are required for catalytic proteins of mTOR
What is the function of FRB region
targeted by rapamycin FKBP12 COMPLEX
What is the function of the kinase region
phosphorylate target proteins and is embedded in catalytic domain
what is the function of the negative regulatory domain (NRD)
contains specific serine and threonine amino acids which are phosphorylated by other cellular kinases
why is the phosphorylation site important
phosphorylation site is important for the regulation of mTOR activities
what are the two multiprotein cellular complexes
mTOR 1 and mTOR 2
What is the mechanism of action of rapamycin
prevents assembly of m TOR 1. but doesn’t affect mTOR 2 as it contains distinct proteins that can still bind to m TOR even in the presence of rapamycin
what are the similarities between mTORC 1 and 2
- deptor
- mLST8
- mTOR
what are the differences between mTORC 1 and 2
mTORC 1: pras40,raptor
mTORC 2: protor, siin 1, rictor
what is the function of FKB12 in mTORC 1
disrupts the interaction between mTOR and raptor
what is the function of mLST8
associated wit the catalytic domain of mTOR by stabilising kinase activation loop of mTOR
if mLST8 is removed is mTOR still functional? (1)
yes
what is the function of pras40 and deptor (1)
inhibitory subunits
what is the function of a raptor (1)
facilitates the recruitment of different mTOR substrates which will later be phosphorylated by mTOR this is done by binding to specific protein motif
Does raptor require subcellular localisation? (1)
yes
what is the function of sin 1,protor and deptor (2)
regulatory proteins
what is the function of rictor (2)
rapamycin-insensitive companion of mTOR. recruits substrates proteins for phosphorylation by mTOR
what is the function of rapamycin FKB12 in mTORC2
doesn’t ‘t directly bind or inhibit mTORC 2 if the cell is exposed to the long treatment of rapamycin it will cause the inhibition of mTORC2 due to the inability of rapamycin-bound mTOR kinase to incorporate new mTOR2 complexes
explain the role of mTORC1 in upstream regulation of mTOR Complexes
functions as a downstream mediator of several growth factor signalling pathway due to the pathway inhibiting a key -ve regulator of mTOR signalling tuberous sclerosis complex (TSC)
mTORC 1 activation is controlled by
nutrient availability from food so activated after feeding to promote growth and energy storage in tissue
is mTORC1 inhibited during fasting
yes to conserve limited energy
what does upstream regulation of mTOR complexes do
regulates cellular growth and proliferation
explain the activation of mTORC 1 by Rheb
TSC acts as GTPase GTPase-activating protein(GAP) for Rheb Directly binds and activates mTORC1
What is TSC
tuberous sclerosis complex
the Rheb GTPase
small Rheb GTPase continuously cycles in its inactive form GDP bound form and active GTP bound form and is regulated by the activity of GEF an GAD
what is GAP
stands for GTPase-activating protein which activates GDP-bound (INACTIVE) form of GTPase.
what is GEF
stands for Guanine nucleotide exchange factor which promotes active GTP bound form of protein
where is rheb found
lysosome membrane
describe the activation of mTORC1 by Rheb
growth factor signalling (such as insulin growth factor) leads to the phosphorylation of TSC which inhibits phosphorylation GAP activity causing Rheb to be activated by promoting rhebGTP so leads to activation of mTORC 1
How do amino acids stimulate mTORC 1
-feeding leads to an increase in aa levels
- aa is sensed by RAG GTPase in mTORC1
- aa simulation converts RAG to active GTP bound state which means they can bind to raptor which stimulates mTORC formation at lysosome membrane
- raptor & mTORC1 in lysosomal membrane the RAG promote the association between mTOR and rheb once complex is formed it can be activated by rheb at cellular localisation
what are RAG
Obligate-heterodimers made up of RAG A/B or RAG C/D
describe the negative regulation of mTORC1 by AMPK
mTORC1 also responds to intracellular and environmental stressors which are incompatible with growth ex; low ATP levels. AMPK can directly regulate mTORC1 by phosphorylating the raptor at an inhibitory site. If cellular energy levels are down during glucose deprivation; the AMP: ATP ratio within the cell will change which activates AMP Kinase(inhibits mTORC1 directly by phosphorylating the TSC at the activation site which means rheb becomes inactive in its GDP-bound form before inactivating mTORC action/
what is the regulation of mTORC2 activated by
insulin signalling by P13
Describe how the regulation of mTORC2 is activated by insulin signalling by P13 kinase
in the absence of insulin, mTORC2 will be inactive once insulin binds to both activated P13 kinase and activated AKT can phosphorylate and activate mTORC2
what is mTORC1 responsible for
regulating the balance between anabolism and catabolism in response to environmental conditions
downstream signalling by mTORC1
mTORC1 activity will phosphorylate S6K causing it to be activated=> it then goes on to phosphorylate substrates and initiation factors that promote the formation and function of 5’ cap of mRNA
