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Apology and Disclosure of Class Schedule

  • Instructor apologizes for confusion regarding Thursday's class and reading assignment.
  • Personal family medical emergency resulted in chaos and lack of preparation.
  • Exam grades are delayed due to this situation and will be available by Thursday or possibly next Monday.
  • Spouse undergoing surgery tomorrow may affect class format.
  • Class will happen but may be hosted digitally or in person, decision to be communicated by email at 06:00 AM the day after.

Review of Intracellular Signaling

  • Intracellular Signaling Cascades
      - Discussion on intracellular signaling and specific cascades.
      - Focus on the role of receptors in activating signaling pathways.
      - Highlighting the concept of cascading secondary messenger systems.
  • Kinases and Phosphatases
      - Importance of phosphatases in balancing activated and inactivated states.
      - Understanding the function of kinases:
        - Kinases typically add phosphate to proteins leading to activation.
        - Phosphorylation alters the protein's energy landscape, shape, and function, not merely an on/off switch.
      - Kinases turn inactive when awaiting activation signals; this usually involves regulatory and catalytic domains.

Mechanism of Kinase Activation

  • Dynamic of Kinase Activation
      - Kinases have hidden catalytic domains that are released upon binding of regulatory domains by various chemical signals (e.g., calcium, dioxylicerol).
      - Example: Protein Kinase A (PKA)
        - PKA is a tetramer made up of two regulatory and two catalytic subunits.
        - PKA remains inactivated when regulatory domains bind to catalytic domains.
        - Activation occurs when cyclic AMP binds to regulatory domains, causing them to change shape and release catalytic domains.
  • Feedback Mechanism
      - Once sufficient phosphorylation occurs, cyclic AMP levels decrease, re-binding regulatory domains to catalytic domains, returning PKA to an inactive state.
      - The finely tuned regulation is crucial for cellular functions and responses.

Effects of PKA on Cellular Processes

  • PKA can:
      - Lead to direct phosphorylation of proteins, thus altering their activity.
      - Regulate protein synthesis by affecting DNA binding proteins (regulatory elements).
      - Phosphorylation can lead to the activation of genes by enhancing interactions with transcription factors.

Diversity of Kinases in Cellular Signaling

  • Multiple kinases provide specificity in phosphorylation, allowing tailored responses to various stimuli.
  • Examples of different kinases include:
      - Protein Kinase C (PKC)
        - Functions similarly to PKA but binds diacylglycerol and calcium rather than cyclic AMP.
        - Involvement in different signaling mechanisms focused on a unique biochemical landscape.
      - Calmodulin Dependent Protein Kinases (CaMK)
        - Specifically CaMK II, heavily expressed in excitatory neurons and serves as a marker for neuronal activity.
  • CaMK II mechanism:
      - Involves binding with calmodulin, a calcium-binding protein, which, once calcium is present, reveals the catalytic domain for phosphorylation processes.

Role of Calcium in Kinase Activation

  • Calmodulin acts as a calcium modulator, allowing calcium to interact with various proteins that otherwise couldn’t directly bind to calcium.
  • Possible post-translational modifications of calmodulin enhance its binding interactions with numerous proteins.

Long-term Potentiation (LTP)

  • Phosphorylation is crucial in mediating synaptic plasticity, determining neuronal strengthening during synaptic activity.
  • By inhibiting various kinases (PKA, PKC, CaMK II), the impact on excitatory postsynaptic currents (EPSCs) can provide insight into kinase functions.
  • Mechanistic interrogation involves understanding a protein’s role by inhibiting its activity and observing resultant changes in cellular responses.

MAPK Pathway Overview

  • Mitogen Activated Protein Kinase (MAPK) Pathway
      - Distinct from phosphorylation events in the cell; focuses on translocating proteins to the nucleus for gene activation.
      - MAPK can be interchangeably referred to as RAS/RAF/MEK/ERK in older literature.
  • Receptor Tyrosine Kinases (RTKs) catalyze a series of phosphorylation events leading to activation of RAS and subsequent MAPK cascades influencing gene expression.

Interaction of BDNF with TRKB Receptors

  • Brain-Derived Neurotrophic Factor (BDNF) interacts with TRKB, a receptor that initiates multiple signaling pathways, promoting neuronal health, growth, and stability.
  • This multifaceted interaction underscores the potency and regulatory capabilities of BDNF for neuron behavior.

Gene Expression and Transcription Factors

  • All cellular signaling ultimately leads to gene expression changes; transcription factors play a pivotal role.
  • CREB (Cyclic AMP Response Element Binding Protein) is crucial in neuronal signaling:
      - Activated CREB leads to further expression of transcription factors and genes like cFos, crucial for neural plasticity and activity tracking.
  • Understanding how signaling pathways integrate to regulate gene expression provides insight into cell dynamics and adaptability to various stimuli.

Summary of Cellular Mechanisms

  • All cellular interactions form complex networks involving various kinases, phosophatases, signaling pathways, and transcription factors.
  • Key takeaway: cellular signaling is highly regulated and subject to intricate feedback mechanisms, crucial for maintaining homeostasis and facilitating appropriate cellular response.
  • Discussion of the final exam scheduled for May 12 at 2 PM, and reminder for students to check for an email about class format upcoming class.