BIO 320 Chapter Notes - Chapter 15: Membrane Transport Protein, Calmodulin, Quaternary
Chapter 15 Cell Signaling: Cell Signaling II (pg 840-849)
• Ca2+/calmodulin-dependent protein kinases mediate many responses to Ca2+ signals
o Calmodulin – most important Ca2+-binding proteins that relays the cytosolic Ca2+ signal
▪ Governs many Ca2+-regulated processes
▪ Structure: high conserved, single polypeptide chain with four high-affinity Ca2+
binding sites and undergoes conformational change after binding Ca2+
▪ Sigmoidal response
▪ Then goes on to bind and activate other proteins such as enzymes and
membrane transport proteins
o I.e. binds to Ca2+ pump in plasma membrane to return cytosolic
concentrations to regular levels
• Can serve as a permanent regulatory subunit of an enzyme complex
o Ca2+/calmodulin-dependent kinases (CaM-kinases) – family of protein kinases that
indirectly mediates Ca2+ effects through protein phosphorylations
▪ Can inhibit transcriptions of certain genes (I.e. CREB protein)
▪ CaM-kinase II – found in most animal cells but especially in the nervous system
• Special quarternary structure
o Twelve rings copies of the enzyme into a stacked pair of rings
with kinase domains on the outside that are linked to a central
hub
o Allows it to function as a memory device switching between
inactive and active with Ca2+ signal
• Autophosphorylation – done by adjacent kinase subunits with
Ca2+/calmodulin can activate them
o Enzyme maintains activity even after signal leaves until the
kinase gets shut off
• Can also use intrinsic memory mechanism to decode frequencies of
Ca2+ oscillations, which is especially important at nerve cell synapse
• Enzyme activity increases when exposed to both a protein phosphatase
and repetitive pulses of Ca2+/calmodulin
• Some G proteins directly regulate ion channels
o G proteins can regulate in ways aside from regulating membrane-bound enzymes that
alter cAMP and Ca2+ concentrations
o They can activate a GEF that activates a monomeric GTPase that regulates the actin
cytoskeleton
o Ca also diretly ative or iativate io haels to hage the plasa erae’s io
permeability
▪ I.e. acetyl choline redues heart rate fro reeptors that ativate G protei’s
beta gamma subunit to bind to K+ channels to open them, which makes it
harder to depolarize the cell
▪ Muscarinic acetylcholine receptors – activated by fungal alkaloid muscarine
find more resources at oneclass.com
find more resources at oneclass.com
