Signal Transduction
The soluble second messenger in the Gq-coupled signaling pathway
What is IP3?
Large GTPases are often described as “molecular machines” rather than simple molecular switches. What does this mean, and how is this different from small GTPases such as Ras?
Large GTPases are called molecular machines because they use GTP binding and hydrolysis to drive large conformational changes, oligomerization, and mechanical work, such as membrane constriction, membrane fusion, organelle division, or immune defense. In contrast, small GTPases like Ras mainly act as molecular switches, cycling between an active GTP-bound state and an inactive GDP-bound state to regulate signaling pathways. Large GTPases often physically remodel cellular structures, while small GTPases more commonly regulate downstream proteins.
The site of GRK-mediated phosphorylation on the receptor
What is the distal end of the C-terminal tail?
The receptor component that is typically mutated in TSH GOF mutations, and how this mutation contributes to the hyperthyroidism
What is TMD6 remaining in the ligand-bound conformation, resulting in constitutive signaling even in the absence of ligand and elevated TSH levels impacting metabolism
The immediate (ionic) effects of Gq and some Gs-coupled cascades are accomplished by this method (50 points per correct answer)
What is....beta-gamma subunit activation of ion channels (Gs) and IP3-mediated calcium flux from IP3Rs on the ER (Gq)
Name each of the signal amplification steps in the Gs and Gq-coupled signaling pathways (50 points per)
What are...
a) AC converting ATP --> cAMP
b) PKA phosphorylating multiple downstream protein targets
c) PKC phosphorylating downstream targets
d) CamKII-mediated phosphorylation
e) Calcium-mediated signaling in general
Choose one example of a large GTPase and explain how GTP hydrolysis contributes to its biological function
One example is dynamin, a large GTPase involved in endocytosis. Dynamin assembles around the neck of a budding vesicle at the plasma membrane. When dynamin binds and hydrolyzes GTP, it undergoes conformational changes that help constrict the vesicle neck and promote membrane fission. This allows the vesicle to pinch off from the plasma membrane and enter the cell.
A second acceptable example would be Drp1, which assembles around mitochondria and uses GTP hydrolysis to help constrict and divide mitochondria during mitochondrial fission.
Give examples of GPCR crosstalk (50 points per)
Beta-gamma subunit mediated Calcium release (Gs) triggering Gq-pathway effectors
Kinases (PKA, PKC, etc) phosphorylating enzymes in other pathways such as AC
Receptor heterodimerization "hijacking" another receptor to signal via that pathway with a differing external ligand
The various ways that a LOF mutation can occur in GPCRs (total of four, 50 poins for each correct answer)
What are:
1) protein misfolding
2) alteration to binding pocket shape
3) alteration to the GPCR domain interacting with the alpha subunit
4) alteration to the GRK substrate region, increasing GRK-mediated internalization in absence of ligand binding
The mechanism by which GPCR activation can exert long-term effects on the cell, long after ligand dissociation (bonus: list the response elements for Gs and G12/13 respectively)
What is.... regulation of gene expression via downstream phosphorylation of protein targets like transcription factors
bonus: cAMP response element (CRE) for Gs and serum response element (SRE) for G12/13.