1. Calcium Bioinorganic Perspectives
Edwin Ragwan

2. Calcium History Why calcium? Proteins that regulate concentration
Concentration of calcium
Proteins that regulate concentration
EF-Hand Motif
Calmodulin (similar to Troponin C)
Calbindin
Connection with Paper

3. History of Calcium Latin “calx” meaning lime
Calcium compounds dates back to
975 AD - Plaster of Paris for bones
Mayan ruins - limestone for mortar
Calcium as metal, 1808 by Humphry Davy
Electrolysis of mixture of lime and mercuric oxide

4. Why Calcium?
“Vitamin D-Enhanced Duodenal Calcium Transport” Wongdee & Charoenphandhu, 2005
Fundamental to cellular organ functions
~99% of total body calcium
Hydroxyapatite, amorphous calcium phosphate & free-ionized Ca2+
Most abundant mineral element found in our bodies

5. Biomineralization of Calcium
Hydroxyapatite, Ca10(PO4)6(OH)2
Structural support, mechanical strength
Bone and teeth
Biologically controlled biomineralization
Well-regulated, well-defined structures and shapes
Amorphous calcium phosphate, Ca3/4Hy(PO4)z· nH2O
Storage
Often results from metabolic processes
Biologically induced

6. Why Calcium?
“Vitamin D-Enhanced Duodenal Calcium Transport” Wongdee & Charoenphandhu, 2005
Fundamental to cellular organ functions
~99% of total body calcium
Hydroxyapatite nanocrystals, amorphous calcium phosphate & free-ionized Ca2+
Prime movers in an intracellular regulatory system in all eukaryotic systems
Hypocalcemia or hypercalcemia is lethal

7. Concentration of Ca2+ Compartments Intracellular Ca2+
Bone, extra and intracellular fluids
Excretion through urine, uptake through intestines, release/uptake in bones
Intracellular Ca2+
Total vs. free Ca2+
How to monitor?
Methods of maintenance
Calcium pumps & calcium binding proteins
,000 times lower in blood
Thermofisher

8. Proteins that Regulate Ca2+
Ca2+ binding proteins
Calmodulin
Ca2+ dependent intracellular regulatory networks
Troponin C
Muscle contraction
Calbindin
Vitamin D uptake of Ca2+ from intestine
Transport of Ca2+ through epithelial cells of placenta
Buffering/storage role

9. EF-Hand Motif Helix-loop-helix structural domain
Two alpha helices linked by short loop

10. EF-Hand Motif 12 amino acids surrounding Ca2+
Highly conserved Asp1, Gly6, Glu12
Side chains of 1, 3, 5 and 12 are ligands, as well as backbone carbonyl of 7
9 is either ligand or hydrogen bonded to water
12 has bidente ligand
How many ligands? What’s possible geometry?

11. EF-Hand Motif
Zhou, et al., 2009
Ef-Hand

12. Calmodulin/Troponin C
Recall:
Calmodulin: Ca2+ dependent intracellular regulatory networks
Troponin C: Muscle contraction
Contains two pairs of EF-Hand motif on each end
Structural change related to metal ion binding
C. Ban, et al., 1994
Dutta & Goodsell, 2003

13. Calmodulin/Troponin C
Mechanism
dumbbell-shape of two globular domains connected together by a flexible linker
Each end binds to two calcium ions
EF hands contain electronegative environment for Ca2+
Binding causes change
Dutta & Goodsell, 2003

14. Calbindin Recall: Contains pair of EF Hand motif
Vitamin D uptake of Ca2+ from intestine
Transport of Ca2+ through epithelial cells of placenta
Contains pair of EF Hand motif
One pseudo-EF-Hand
Binding has little effect on apo-form

15. Calbindin
F. J. van de Graaf, et al., 2006

16. Connection to Paper Cytoplasmic Translocation
Free vs. protein bound
Excess calcium may cause havoc
Calmodulin: can deactivate TRPV6
Calbindin: buffers cytoplasmic calcium
Wongdee & Charoenphandhu, 2005

17. The Mg2+ Consideration Mg2+ is abundant (mM)
Affinity of EF Hand to Mg2+ is observed
Implications for Ca2+ activation
M. Anderson, et al., 1997

18. Further Work More Structures of Mg2+ bound Role of pseudo-EF-hand
Why and how Mg2+ resembles apo form?
Role of pseudo-EF-hand
How this prevents total conformational change upon binding to Ca2+?
Role of Vitamin D
How does this correlate to mRNA and or protein expression of calcium binding proteins?

19. Conclusion Calcium’s role in biological systems
Concentration
Regulated by calcium binding proteins
Calbindin/Troponin C/Calmodulin
EF Hand motif
Utilizes metal for structural integrity and induce structural change
Pseudo-EF-hand does not undergo conformational change
Ca2+ is tightly regulated

20. References
Bertini, I. Biological inorganic chemistry: structure and reactivity
Royal Society of Chemistry. Calcium. 2016
Shuchismita D, D Goodsell. Calmodulin. 2003
Wongdee K, Charoenphandhu N. Vitamin D-Enhanced Duodenal Calcium Transport. 2005