Hemoglobin Hb : Function, Structure and Relevance to daily life. By Arwa Almejbel CHE442:Proteins Dr.Jon Friesen 1

Introduction First studied in the 1800 ’ s. Found in bacteria,eukaryotic organisms and archea. The heme part is synthesized in mitochondria and cytosol. While the globin protein parts are synthesized by ribosomes in the cytosol. Function: to transport the oxygen and maintain the round shape of the RBCs. 2

Hemoglobin A Structure Heme Red is Heme, gray is α chain and blue is β chain. PDB ID: 1HGA α1α1 β1β1 β2β2 α2α2 3

Amino acid sequence Alignment 4 Glu6Gly26Phe44 Val60His63His9 2 Lys95 Tyr145

Key amino acids in Hemoglobin His143 (brown), Lys82(orange), and His2(brown), interact with 2,3-BPG in the center of the tetramer holding the deoxyhemoglobin form in place (salt bridges). His63, His92 (brown) are important for hemoglobin binding oxygen. Phe44(green),Tyr142 (purple)stabilize the structure by forming hydrogen bonds between helices. Glu6(blue) is an important in mutagenesis studies. Gly26 (yellow)is very small which allows 2 helices to approach each other. 5 PDB ID: 1HGA

Oxygen binding Cooperative binding Binding to the 1 st O 2 facilitates the binding of 2 nd,3 rd and 4 th O 2. Binding to O 2 causes conformational changes. PDB ID: 1hho 6

The T and R transition 7 1 Image: 2 Shaanan, B. Structure of human oxyhaemoglobin at 2.1 A resolution. (1983) J.Mol.Biol. (171) 31-59

Salt Bridges in Deoxy Hb 8 Salt links (ionic interactions) between 2,3-BPG's negatively charged groups (2 phosphates and a carboxyl group) and positively charged groups on the protein. several basic groups (Lys and His R groups, and the N-terminal a-amino group) on BOTH b chains Salt links effectively cross-link the quaternary structure across the central cavity in the T state. Hb(BPG) [T state] + O 2  Hb(O 2 ) [R state] + BPG

Oxygen-Hemoglobin binding 9 Partial pressure of oxygen determines how much oxygen binds. 2,3-BPG reduces Hb affinity to O 2 and increases O 2 release in tissues. Small amount of CO reduces Hb ability to transport O 2.

Mutations in hemoglobin (hemoglobinopathies): Sickle cell anemia (Hb S): 1 Image: 2 Marengo-Rowe,A. J. (2006) Structure-function relations of human hemoglobins. Proc (Bayl Univ Med Cent)19(3) 239–

structure 11 PDB ID: 1GZX

Hydrophobic pocket PDB ID: 2HBS Val6, Leu88, Phe85 12

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Sickle cell trait (Hb AS)fights Malaria 14 1 Aidoo, M., Terlouw, D.J., Kolczak, M.S., McElroy, P.D., ter Kuile, F.O., Kariuki, S., Nahlen, B.L., Lal,A.A., Udhayakumar, V.(2002) Protective Effects of the Sickle Cell Gene Against Malaria Morbidity and Mortality. Lancet (359) Luzzatto, L., Nwachuku-Jarrett, E.S., Reddy, S.( 1970) Increased sickling of parasitised erythrocytes as mechanism of resistance against malaria in the sickle-cell trait. Lancet 1(7642) Gong, L., Parikh, S., Rosenthal, P.J. (2013) Biochemical and Immunological Mechanisms by Which Sickle Cell Trait Protects Against Malaria. Malar J. 12(317).

References Harrington, D.J., Adachi, K., Royer Jr., W.E. (1997) The high resolution crystal structure of deoxyhemoglobin S. J.Mol.Biol. 272: Shaanan, B. Structure of human oxyhaemoglobin at 2.1 A resolution. (1983) J.Mol.Biol. (171) Marengo-Rowe,A. J. (2006) Structure-function relations of human hemoglobins. Proc (Bayl Univ Med Cent)19(3) 239–245. Paoli, M., Liddington, R., Tame, J., Wilkinson, A., Dodson, G. (1996) Crystal structure of T state haemoglobin with oxygen bound at all four haems. J.Mol.Biol. 256(4): PDB ID: 1BBB Liddington, R., Derewenda, Z., Dodson, E., Hubbard,R, and Dodson, G. (1992) High resolution crystal structures and comparisons of T-state deoxyhaemoglobin and two liganded T-state haemoglobins: T(alpha- oxy)haemoglobin and T(met)haemoglobin. J Mol Biol. 228(2) PDB ID: 1HGA Starr C., Taggart, R. (2001) Biology: The Unity and Diversity of Life (6 th Ed.) pp , Brooks/Cole, Pacific Grove. Rousseot, N., Jaenicke, E., Lamkemeyer, T., Harris, J.R., Pirow, R. (2006) Native and subunit molecular mass and quarternary structure of the hemoglobin from the primitive branchiopod crustacean Triops cancriformis. FEBS J 17, Campbell, N.A., Reece, J.B., Taylor, M.R., Simon, E.J. (2006) Biology Concepts and Connections (Eds.) (5 th Ed.) pp , Pearson, San Francisco. Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., Walter, P. (2002) Molecular Biology of the Cell. (Eds.), pp. 461, Garland Science, New York. Aidoo, M., Terlouw, D.J., Kolczak, M.S., McElroy, P.D., ter Kuile, F.O., Kariuki, S., Nahlen, B.L., Lal,A.A., Udhayakumar, V.(2002) Protective Effects of the Sickle Cell Gene Against Malaria Morbidity and Mortality. Lancet (359)