BIOL 2021 Lecture Notes - Lecture 13: Membrane Transport Protein, Calmodulin, Conformational Change
13 May 2018
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Feb 15th (Lecture 12)
Continuing chapter 15
• G protein receptor → ligand activates it → activates a trimeric G protein → picks
up GTP → activates enzyme downstream (phospholipase C beta) → PIP2 →
DAG is produced → IP3 → binds to Ca2+ channels → Ca2+ comes out →
activated protein kinase C.
• Calcium signalling (838, 840-841), regulation of Ca+
o Ca2+ is toxic to cells. The levels have to be kept low in the cytosol.
o Ca2+ inside = 10^-7 M, outsie = 10^-3 M.
o PM: Na2+/Ca2+ exchanger, Ca2+ pump (uses ATP to push something
against gradient → out of cytosol).
o ER: Ca2+ pumped in.
• Question: why do cells use Ca2+ at an intracellular concentration of 10^-7M for
signalling rather than Na+ at 10^-3M?
o Answer: when you want to signal, you want something obvious.
o Large changes in Ca2+ concentration will result from influx of fewer ions.
Large changes in Na+ conc would be hard to achieve.
• Calmodulin (CaM), Fig 15-33 calmodulin:
o Has 4 binding sites for calcium. Binds Ca and undergoes conformational
change.
o Ca2+/calmodulin has no enzymatic activity itself but instead acts by
binding to and activating other proteins. Binds to other proteins to activate
when calcium is bound. Conformational change happens.
o Targets = enzymes, membrane transport proteins, protein kinases.
o Ca2+/calmodulin dependent kinases (CaM-kinases). Many effects of Ca2+
are mediated by protein phosphorylations catalyzed by a family of protein
kinases called CaM-kinases.
o CaM-Kinase phosphorylate proteins such as (but not always) gene
regulatory proteins on Ser/Thr.
• Classification of receptors → targets are ion channels.
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