Lactoferrin is an iron-binding diferric glycoprotein present in most of the exocrine secretions. The major role of lactoferrin, which is found abundantly in colostrum, is antimicrobial action for the defense of mammary gland and the neonates. Lactoferrin consists of two equal halves, designated as N-lobe and C-lobe, each of which contains one iron-binding site. While the N-lobe of lactoferrin has been extensively studied and is known for its enhanced antimicrobial effect, the C-lobe of lactoferrin mediates various therapeutic functions which are still being discovered. The potential of the C-lobe in the treatment of gastropathy, diabetes, and corneal wounds and injuries has been indicated. This review provides the details of the proteolytic preparation of C-lobe, and interspecies comparisons of its sequence and structure, as well as the scope of its therapeutic applications. 1. Lactoferrin: A Bilobal Protein Lactoferrin is an iron-binding glycoprotein which is abundantly present in colostrum and is the major mediator of defence for the newborn [1–4]. The three-dimensional structures of lactoferrin from various species, such as human [5, 6], bovine [7, 8], buffalo [9, 10], equine [11, 12], and camel [13] have been solved. In all these cases, the overall structures of iron-saturated lactoferrin were found to have a similar folding. Lactoferrin is an 80？kDa single-chain glycoprotein which can be equally divided into two homologous halves, N-lobe and C-lobe, each of which is about 40？kDa in size and is connected to the other by a short helical segment (Figure 1). Each lobe is further subdivided into two domains, which are designated as N1 and N2 domains of N-lobe and C1 and C2 domains of C-lobe. The iron-binding site is situated inside the interdomain cleft in each lobe. The iron-binding site consists of four residues 2 tyrosines, 1 aspartate, and 1 histidine residues. The iron-binding residues in N-lobe are Asp 60, Tyr 92, Tyr 192, and His 253 while the corresponding iron-binding residues in C-lobe are Asp 395, Tyr 433, Tyr 526, and His 595. The iron-binding residues are coordinated to the ferric ion and a synergistic bidentate carbonate anion (Figure 2). Figure 1: Schematic diagram of the bovine lactoferrin molecule (PDB code: 1BLF). The N1 and N2 domains are colored in yellow and pink, respectively, while the C1 and C2 domains are colored in green and blue, respectively. The interconnecting helix between the lobes is colored in orange. The two iron atoms are shown as red spheres. Figure 2: Schematic figure of the iron-binding site of lactoferrin. The
References
[1]
P. L. Masson and J. F. Heremans, “Metal-combining properties of human lactoferrin (red milk protein). 1. The involvement of bicarbonate in the reaction,” European Journal of Biochemistry, vol. 6, no. 4, pp. 579–584, 1968.
[2]
P. L. Masson and J. F. Heremans, “Lactoferrin in milk from different species,” Comparative Biochemistry and Physiology B, vol. 39, no. 1, pp. 119–129, 1971.
[3]
R. R. Arnold, M. F. Cole, and J. R. McGhee, “A bactericidal effect for human lactoferrin,” Science, vol. 197, no. 4300, pp. 263–265, 1977.
[4]
J. Brock, “Lactoferrin in human milk: its role in iron absorption and protection against enteric infection in the newborn infant,” Archives of Disease in Childhood, vol. 55, no. 6, pp. 417–421, 1980.
[5]
B. F. Anderson, H. M. Baker, G. E. Norris, D. W. Rice, and E. N. Baker, “Structure of human lactoferrin: crystallographic structure analysis and refinement at 2.8 ？ resolution,” Journal of Molecular Biology, vol. 209, no. 4, pp. 711–734, 1989.
[6]
G. B. Jameson, B. F. Anderson, G. E. Norris, D. H. Thomas, and E. N. Baker, “Structure of human apolactoferrin at 2.0 ？ resolution. Refinement and analysis of ligand-induced conformational change,” Acta Crystallographica Section D: Biological Crystallography, vol. 54, no. 6, pp. 1319–1335, 1998.
[7]
M. Haridas, B. F. Anderson, H. M. Baker, G. E. Norris, and E. N. Baker, “X-ray structural analysis of bovine lactoferrin at 2.5 ？ resolution,” Advances in Experimental Medicine and Biology, vol. 357, pp. 235–238, 1994.
[8]
S. A. Moore, B. F. Anderson, C. R. Groom, M. Haridas, and E. N. Baker, “Three-dimensional structure of diferric bovine lactoferrin at 2.8 ？ resolution,” Journal of Molecular Biology, vol. 274, no. 2, pp. 222–236, 1997.
[9]
S. Karthikeyan, S. Yadav, M. Paramasivam, A. Srinivasan, and T. P. Singh, “Structure of buffalo lactoferrin at 3.3 ？ resolution at 277 K,” Acta Crystallographica Section D: Biological Crystallography, vol. 56, no. 6, pp. 684–689, 2000.
[10]
S. Karthikeyan, M. Paramasivam, S. Yadav, A. Srinivasan, and T. P. Singh, “Structure of buffalo lactoferrin at 2.5 ？ resolution using crystals grown at 303 K shows different orientations of the N and C lobes,” Acta Crystallographica Section D: Biological Crystallography, vol. 55, no. 11, pp. 1805–1813, 1999.
[11]
A. K. Sharma, M. Paramasivam, A. Srinivasan, M. P. Yadav, and T. P. Singh, “Three-dimensional structure of mare diferric lactoferrin at 2.6 ？ resolution,” Journal of Molecular Biology, vol. 289, no. 2, pp. 303–317, 1999.
[12]
A. K. Sharma, K. R. Rajashankar, M. P. Yadav, and T. P. Singh, “Structure of mare apolactoferrin: the N and C lobes are in the closed form,” Acta Crystallographica Section D: Biological Crystallography, vol. 55, no. 6, pp. 1152–1157, 1999.
[13]
J. A. Khan, P. Kumar, M. Paramasivam et al., “Camel lactoferrin, a transferrin-cum-lactoferrin: crystal structure of camel apolactoferrin at 2.6 ？ resolution and structural basis of its dual role,” Journal of Molecular Biology, vol. 309, no. 3, pp. 751–761, 2001.
[14]
J. H. Brock, F. Arzabe, F. Lampreave, and A. Pineiro, “The effect of trypsin on bovine transferrin and lactoferrin,” Biochimica et Biophysica Acta, vol. 446, no. 1, pp. 214–225, 1976.
[15]
D. Legrand, J. Mazurier, and M. H. Metz Boutigue, “Characterization and localization of an iron-binding 18-kDa glycopeptide isolated from the N-terminal half of human lactotransferrin,” Biochimica et Biophysica Acta, vol. 787, no. 1, pp. 90–96, 1984.
[16]
C. L. Day, K. M. Stowell, E. N. Baker, and J. W. Tweedie, “Studies of the N-terminal half of human lactoferrin produced from the cloned cDNA demonstrate that interlobe interactions modulate iron release,” Journal of Biological Chemistry, vol. 267, no. 20, pp. 13857–13862, 1992.
[17]
B. Sheth, K. M. Stowell, C. L. Day, E. N. Baker, and J. W. Tweedie, “Cloning and expression of the C-terminal lobe of human lactoferrin,” Advances in Experimental Medicine and Biology, vol. 357, pp. 259–263, 1994.
[18]
S. Sharma, T. P. Singh, and K. L. Bhatia, “Preparation and characterization of the N and C monoferric lobes of buffalo lactoferrin produced by proteolysis using proteinase K,” Journal of Dairy Research, vol. 66, no. 1, pp. 81–90, 1999.
[19]
W. S. Kim, K. I. Shimazaki, and T. Tamura, “Expression of bovine lactoferrin C-lobe in Rhodococcus erythropolis and its purification and characterization,” Bioscience, Biotechnology and Biochemistry, vol. 70, no. 11, pp. 2641–2645, 2006.
[20]
S. Sharma, J. Jasti, J. Kumar, A. K. Mohanty, and T. P. Singh, “Crystal structure of a proteolytically generated functional monoferric C-lobe of bovine lactoferrin at 1.9 ？ resolution,” Journal of Molecular Biology, vol. 331, no. 2, pp. 485–496, 2003.
[21]
Y. Liao, E. El-Fakkarany, B. L？nnerdal, and E. M. Redwan, “Inhibitory effects of native and recombinant full-length camel lactoferrin and its N and C lobes on hepatitis C virus infection of Huh7. 5 cells,” Journal of Medical Microbiology, vol. 61, part 3, pp. 375–383, 2012.
[22]
M. G. Ammendolia, M. Agamennone, A. Pietrantoni, et al., “Bovine lactoferrin-derived peptides as novel broad-spectrum inhibitors of influenza virus,” Pathogens and Global Health, vol. 106, no. 1, pp. 12–19, 2012.
[23]
R. Mir, N. Singh, G. Vikram et al., “The structural basis for the prevention of nonsteroidal antiinflammatory drug-induced gastrointestinal tract damage by the C-lobe of bovine colostrum lactoferrin,” Biophysical Journal, vol. 97, no. 12, pp. 3178–3186, 2009.
[24]
R. Mir, N. Singh, G. Vikram et al., “Structural and binding studies of C-terminal half (C-lobe) of lactoferrin protein with COX-2-specific non-steroidal anti-inflammatory drugs (NSAIDs),” Archives of Biochemistry and Biophysics, vol. 500, no. 2, pp. 196–202, 2010.
[25]
R. Mir, R. P. Kumar, N. Singh et al., “Specific interactions of C-terminal half (C-lobe) of lactoferrin protein with edible sugars: binding and structural studies with implications on diabetes,” International Journal of Biological Macromolecules, vol. 47, no. 1, pp. 50–59, 2010.
[26]
B. Ashby, G. Qian, and W. Mark, “Bovine lactoferrin structures promoting corneal epithelial wound healing in vitro,” Investigative Ophthalmology and Visual Science, vol. 52, no. 5, pp. 2719–2726, 2011.
[27]
M. M. Rahman, W. S. Kim, T. Ito, H. Kumura, and K. I. Shimazaki, “Growth promotion and cell binding ability of bovine lactoferrin to Bifidobacterium longum,” Anaerobe, vol. 15, no. 4, pp. 133–137, 2009.
[28]
M. Rahman, W. S. Kim, H. Kumura, and K. I. Shimazaki, “Bovine lactoferrin region responsible for binding to bifidobacterial cell surface proteins,” Biotechnology Letters, vol. 31, no. 6, pp. 863–868, 2009.
[29]
Y. Takayama, K. Mizumachi, and T. Takezawa, “The bovine lactoferrin region responsible for promoting the collagen gel contractile activity of human fibroblasts,” Biochemical and Biophysical Research Communications, vol. 299, no. 5, pp. 813–817, 2002.
[30]
S. E. Babina, D. V. Semenov, V. N. Buneva, and G. A. Nevinsky, “Human milk lactoferrin hydrolyzes nucleoside-5'-triphosphates,” Molekulyarnaya Biologiya, vol. 39, no. 3, pp. 513–520, 2005.
