Streptococcus pneumoniae is a human pathogen bacterium capable of using hemoglobin (Hb) and haem as a single iron source but not in presence of lactoferrin. This bacterium has developed a mechanism through the expression of several membrane proteins that bind to iron sources, between them a lipoprotein of 37 kDa called Spbhp-37 (Streptococcus pneumoniae haem-binding protein) involved in iron acquisition. The Spbhp-37 role is to maintain the viability of S. pneumoniae in presence of Hb or haem. This mechanism is relevant during the invasion of S. pneumoniae to human tissue for the acquisition of iron from hemoglobin or haem as an iron source.
- S. pneumoniae
- iron acquisition
- Hb-binding protein
Iron is required for cellular growth of any bacterial species and it is known that bacterium needs an iron concentration of 10−6–10−8 M [1, 2], however, the concentration of free iron in the human body is usually 10−18 M , lower than bacterial requirements [4, 5, 6]. Therefore, human pathogens often obtain iron from alternative sources available into the body such as lactoferrin (Holo-Lf), hemoglobin (Hb) or even the haem . The success of pathogens to obtain iron from host sources is based on developing different mechanisms, for instance, a direct mechanism which consists of expressing proteins attach to the membrane (termed receptors) [8, 9].
Another mechanism (known as indirect mechanism) is based on secreting siderophores or haemophores to scavenge iron then it is delivering towards a receptor protein . The transportation of iron into the cytoplasm requires proteins as the ATP-binding protein cassette (ABC) , these mechanisms have been established in Gram-negative but not in Gram-positive bacteria.
S. pneumoniaeiron acquisition
3. Hb-binding proteins involved in iron acquisition
Iron is also available in human sources for instance hemoglobin or haem structure within erythrocytes.
4. Hb-iron transporters
The necessity to obtain iron in the human host has provided
5. Which are the amino acid residues of Sphbp-37 haem-binding protein involved in the interaction with the iron source?
5.1 3D modeling of Sphbp-37 protein
To understand more about the interaction between haem-binding protein Sphbp-37 and iron source an
5.2 Interaction of Sphbp-37 protein with haem
We search the amino acids involved in the between Sphbp-37 protein and haem. The molecular dynamic simulation after 500 ns shows an interaction between haem and amino acid residues of Sphbp-37 protein: glutamic acid 152 (Glu152), glutamine 177 (Gln177), valine 178 (Val178), aspartic acid 179 (Asp179), tyrosine 180 (Tyr180), isoleucine 193 (Ile193), alanine 196 (Ala196), glutamine 197 (Gln197) and alanine 200 (Ala200) (Figure 3). We found 10 amino acids involved in the interaction of Sphbp-37 and haem.
5.3 3D model of mutant Sphbp-37 protein (substitutions in 152 and 179 amino acid residues)
To investigate which amino acids of Sphbp-37 protein are involved in haem-binding, we performed a change of glu152 for alanine (glu152ala) and asp179 for alanine ala (asp179ala) (mutant Sphbp-37 protein), these amino acid directly binds the haem. The result showed that the substitution of amino acid in the position 152 and 179 by another amino acid does not allow the binding to the haem. These data shown that amino acids 152 and 179 are essential for haem or Hb-binding and participate direct binding of the iron source.
3D model of mutant Sphbp-37 protein with changes in 152 and 179 amino acid residues was analyzed by NAMD software, the result showed a globular structure inclusive after the changes, however, the binding is not preserved (Figure 4). Mutant Sphbp-37 protein is unable to bind haem these results suggest that amino acids residues of 152 and 179 positions are involved in haem binding directly.
5.4 The promoter region of the spbhp-37 gene does not fur box consensus sequences
Then, we analyzed the
Conflict of interest
The authors declare that they have no conflict of interest.
Ge R, Sun X. Iron trafficking system in Helicobacter pylori. Biometals. 2012; 25:247-258
Klebba PE, McIntosh MA, Neilands JB. Kinetics of biosynthesis of iron-regulated membrane proteins in Escherichia coli. Journal of Bacteriology. 1982; 149:880-888
Raymond KN, Dertz EA, Kim SS. Enterobactin: An archetype for microbial iron transport. Proceedings of the National Academy of Sciences. 2003; 100:3584-3588
Andrews S, Robinsón AK, Rodríguez-Quiñonez F. Bacterial iron homeostasis. FEMS Microbiology. 2003; 27:215-237
Horton R, Moran L, Ochs R, Rawn J, Scrimgeour K. Principles of Biochemistry. 3rd edition. Pearson; 2002. p. 827
Ratledge C, Dover L. Iron metabolism in pathogenic bacteria. Annual Review of Microbiology. 2000; 54:881-941
Wooldridge KG, Williams PH. Iron uptake mechanisms of pathogenic bacteria. FEMS Microbiology. 1993; 12:325-348
Guerinot ML. Microbial iron transport. Annual Review of Microbiology. 1994; 48:743-772
Wandersman C, Delepelaire P. Bacterial iron sources: From siderophores to haemophores. Annual Review of Microbiology. 2004; 58:611-647
Genco CA, Dixon DW. Emerging strategies in microbial haem capture. Molecular Microbiology. 2001; 39:1-11
Miethke M. Iron-responsive bacterial small RNAs: Variations on a theme. Metallomics. 2013; 5:15-28
Butler JC, Schuchat A. Epidemiology of pneumococcal infections in the elderly. Drugs & Aging. 1999; 15:11-19
Gray BM, Converse J, Dillon H. Serotypes of Streptococcus pneumoniaecausing disease. The Journal of Infectious Diseases. 1979; 140:979-983
Musher DM. Infections caused by Streptococcus pneumoniae: Clinical spectrum, pathogenesis, immunity, and treatment. Clinical Infectious Diseases. 1992; 14:801-807
Thornton J, Durick-Eder K, Tuomanen E. Pneumococcal pathogenesis: “Innate invasion” yet organ-specific damage. Journal of Molecular Medicine. 2010; 88:103-107
Yaro S, Lourd M, Traoré Y, Njanpop-Lafourcade BM, Sawadogo A, Sangare L, et al. Epidemiological and molecular characteristics of a highly lethal pneumococcal meningitis epidemic in Burkina Faso. Clinical Infectious Diseases. 2006; 43:693-700
Romero-Espejel ME, González-López MA, Olivares-Trejo JJ. Streptococcus pneumoniaerequires iron for its viability and expresses two membrane proteins that bind haemoglobin and haem. Metallomics. 2013; 5:384-389
Tai SS, Lee CJ, Winter RE. Hemin utilization is related to virulence of Streptococcus pneumoniae. Infectionand Immunity. 1993; 61:5401-5405
Brown JS, Gilliland SM, Holden DW. A Streptococcus pneumoniaepathogenicity island encoding an ABC transporter involved in iron uptake and virulence. Molecular Microbiology. 2002; 40:572-585
Brown JS, Gilliland SM, Ruiz-Albert J, Holden DW. Characterization of pit, a Streptococcus pneumoniaeiron uptake ABC transporter. Infection and Immunity. 2002b; 70(8):4389-4398. DOI: 10.1128/IAI.70.8.4389-4398
Romero-Espejel ME, Rodríguez MA, Chávez-Munguía B, Ríos-Castro E, Olivares-Trejo JJ. Characterization of Spbhp-37, a Hemoglobin-binding protein of Streptococcus pneumoniae. Frontiers in Cellular and Infection Microbiology. 2016; 4(6):47. DOI: 10.3389/fcimb..00047
Yamamoto S, Shinoda S. Iron uptake mechanisms of pathogenic bacteria. Nihon Saikingaku Zasshi. 1996; 51:523-547. DOI: 10.3412/jsb.51.523
Cherayil BJ. The role of iron in the immune response to bacterial infection. Immunologic Research. 2011; 50:1-9. DOI: 10.1007/s12026-010-8199-1
Brock JH. The physiology of lactoferrin. Biochemistry and Cell Biology. 2002; 80(1):1-6. DOI: 10.1139/o01-212
Kawabata H, Sakamoto S, Masuda T. Roles of transferrin receptors in erythropoiesis. Rinsho Ketsueki The Japanese Journal of Clinical Hematology. 2016; 57:951-958. DOI: 10.11406/rinketsu.57.951
Kheirandish M, Motlagh B, Afshar D. Ferritin degradation by pneumococcal HtrA, RadA and ClpP serine proteases: A probable way for releasing and Acquisition of Iron. Infection and Drug Resistance. 2020; 13:3145-3152. DOI: 10.2147/IDR.S264170
Tai SS, Yu C, Lee JK. A solute binding protein of Streptococcus pneumoniaeiron transport. FEMS Microbiology Letters. 2003; 220:303-308. DOI: 10.1016/S0378-1097(03)00135-6
Cheng W, Li Q, Jiang Y-L, Zhou C-Z, Chen Y. Structures of Streptococcus pneumoniaePiaA and its complex with ferrichrome reveal insights into the substrate binding and release of high affinity iron transporters. PLoS One. 2013; 8(8):e71451. DOI: 10.1371/journal.pone.0071451
Vázquez-Zamorano ZE, González-López MA, Romero-Espejel ME, Azuara-Liceaga EI, López-Casamichana M, Olivares-Trejo JJ. Streptococcus pneumoniaesecretes a glyceraldehyde-3-phosphate dehydrogenase, which binds haemoglobin and haem. Biometals. 2014; 27:683-693. DOI: 10.1007/s10534-014-9757-0
Lorenzo V, Giovannini F, Herrero M, Neilands JB. Metal ion regulation of gene expression: Fur repressor–operator interaction at the promoter region of the aerobactin system of pColV-K30. Journal of Molecular Biology. 1988; 203:875-884
Rowland BM, Grossman TH, Osburne MS, Taber HW. Sequence and genetic organization of a Bacillus subtilisoperon encoding 2, 3-dihydroxybenzoate biosynthetic enzymes. Journal of Bacteriology. 1996; 178:119-123
Bsat N, Helmann JD. Interaction of Bacillus subtilisfur (ferric-uptake repressor) with the dhboperator in vitro and in vivo. Journal of Bacteriology. 1999; 181:4299-4307
Heinrich JH, Gatlin LE, Kunsch C, Choi GH, Hanson MS. Identification and characterization of SirA, an iron-regulated protein from Staphylococcus aureus. Journal of Bacteriology. 1999; 181:1436-1443
Masse E, Salvail H, Desnoyers G, Arguin M. Small RNAs controlling iron metabolism. Current Opinion in Microbiology. 2007; 10:140-145
Sánchez-Cruz C, López-Casamichana M, Cruz Castañeda A, Olivares-Trejo JJ. Transferrin regulates mRNA levels of a gene involved in iron utilization in Entamoeba histolytica. Molecular Biology Reports. 2011; 39:4545-4551
Gupta R, Shah P, Swiatlo E. Differential gene expression in Streptococcus pneumoniaein response to various iron sources. Microbial Pathogenesis. 2009; 47:101-109
Hoskins J, Alborn WE, Arnold J, Blaszczak LC, Burgett S, DeHoff BS, et al. Genome of the bacterium Streptococcus pneumoniaestrain R6. Journal of Bacteriology. 2001; 183:5709-5717
Crosa J. Signal transduction and transcriptional and post-transcriptional control of iron-regulated genes in bacteria. Microbiology and Molecular Biology Reviews. 1997; 61:319-336