Calmodulin

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Calcium binding protein involved in intracellular calcium signalling. [1]

Structure

Highly conserved sequence of 152 amino acids [2].

There are four EFh domains which are responsible to bind 4 Ca2+  ions.[3] 

The arrangement of the Ca2+ binding sites are brought about by the N- and C- terminal lobes [4].

Calmodulin are dumbbell shaped protein where long and flexible alpha helix connects two globular domains. Each domain is assembled from two EF-hand regions attached to antiparalel beta-sheet. Ca2+ binds to glutamate and aspartate residues placed in the loop of EF-hand.[5]

It is closely related to Troponin C, which is found in the Actin filaments of Skeletal muscle cells.[6]

Function

Calmodulin functions as a multi-purpose intracellular receptor, governing many Ca2+  regulated processes. [7] 

Two or more Ca2+ ions bind to induce a conformational change and activate calmodulin [8]. This results in amplifying the affinity of Ca2+ molecule which later affects other signalling components such as Ca2+/calmodulin-dependent protein kinases (CaMKs), myosin light chain kinase (MLCK), phosphorylase kinase, neuromodulin and so on [9].

In the case of MLCK, four Ca2+ ions bind Calmodulin to form a Ca2+-CaM complex. It is this complex that then activates MLCK, leading to the Phosphorylation of the myosin light chain and increased ATPase activity in smooth muscle cells. [10]

References

  1. Alberts et al. Molecular Biology of the Cell (5th Ed)
  2. http://www.ncbi.nlm.nih.gov/protein/CAA36839.1
  3. http://smart.embl-heidelberg.de/smart/job_status.pl?jobid=939661123169621289746763YwAuDuwGQT
  4. http://www.cell-signalling.org/csb/004/csb004.pdf
  5. John T.Hancock (2005).Cell signalling. New York:Oxford University press
  6. W.Boron and E Boulpaep, (2012) Medical Physiology (2nd Ed) p258
  7. Alberts et al. Molecular Biology of the Cell (5th Ed).
  8. Alberts et al. Molecular Biology of the Cell (5th Ed)
  9. http://www.cell-signalling.org/csb/004/csb004.pdf
  10. W.Boron and E Boulpaep, (2012) Medical Physiology (2nd Ed) p258
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