Mineralogical Characterization of Chalcopyrite Bioleaching

  • Mejía E
  • Ospina J
  • Osorno L
  • et al.
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role in ligand binding: thus, recombinant I domains reca-pitulate many of the ligand-binding properties of the University of Leicester Leicester LE1 7RH intact integrin (Michishita et al., 1993; Kamata and Ta-kada, 1994; Tuckwell et al., 1995). The first crystal struc-United Kingdom † Department of Biochemistry ture of an I domain showed that it adopts the "dinucleo-tide-binding" fold, with a central mostly parallel sheet University of Cambridge Tennis Court Road surrounded on both sides by amphipathic helices (Lee et al., 1995a). At the C-terminal end of the sheet is a Cambridge CB2 1QW United Kingdom conserved metal binding site that we have called the metal ion-dependent adhesion site or MIDAS motif. Mu-‡ The Burnham Institute 10901 North Torrey Pines Road tagenesis studies show that the MIDAS motif and exposed side chains on the surrounding surface are re-La Jolla, California 92037 quired for ligand binding, and are thus likely to form the ligand contact sites (Michishita et al.. Comparison between We have determined the crystal structure of a complex between the I domain of integrin 21 and a triple two different crystal forms of the M-I domain led us to propose that affinity regulation occurred via changes in helical collagen peptide containing a critical GFOGER motif. Three loops on the upper surface of the I domain metal coordination at the MIDAS motif that were linked to tertiary changes in the domain (Lee et al., 1995b). that coordinate a metal ion also engage the collagen, with a collagen glutamate completing the coordination The 21 integrin is expressed on several different cell types, where it is a receptor for collagen and laminin. sphere of the metal. Comparison with the unliganded I domain reveals a change in metal coordination linked It is required for the arrest of platelets under conditions of blood flow on the collagen fiber surface exposed as a to a reorganization of the upper surface that together create a complementary surface for binding collagen. consequence of injury (Sixma et al., 1997). Recombinant 2-I domain exhibits specific binding to the fibrillar colla-Conformational changes propagate from the upper surface to the opposite pole of the domain, suggesting gens and, like the complete receptor, binds in a cation-dependent manner, being supported by magnesium or both a basis for affinity regulation and a pathway for signal transduction. The structural features observed manganese but not by calcium (Tuckwell et al., 1995; Dickeson et al., 1997). We previously determined the here may represent a general mechanism for integrin-ligand recognition. structure of the 2-I domain in the absence of ligand (Emsley et al., 1997) and showed that it contains an additional helix, called the C helix, protruding from the Introduction upper surface of the domain. Modeling studies with a collagen-like peptide suggested that the C helix would Integrins are the principal family of cell surface proteins play an important role in ligand binding. that interact with the extracellular matrix. These interac-A specific collagen motif recognized by the 2-I do-tions control the adhesion and migration of cells, as well main has recently been identified as the hexapeptide as the transduction of signals that regulate cell growth GFOGER (O hydroxyproline) within the context of a and differentiation (Hynes, 1992). Integrins are heter-collagen triple helix (Knight et al., 2000), and this finding odimers with a generally conserved structure. Cryoelec-has allowed the design of a collagen fragment suitable tron microscopy shows that they have an extracellular for cocrystallization. The recurrent themes of integrin: globular head, 70 A ˚ in diameter, comprising the N-ter-ligand interaction are critical roles for metal ions and minal regions of both and chains, connected via a ligand acidic residues, and the regulation of ligand affin-long (100 A ˚) rigid stalk to a pair of membrane-spanning ity. The crystal structure of an authentic integrin:ligand helices and short C-terminal cytoplasmic tails (Erb et al., fragment presented here demonstrates unequivocally a 1997). The adhesiveness of their extracellular domains is central and direct role for both the metal ion and a ligand allosterically controlled by binding events in the cyto-glutamic acid, and the existence of ligand-induced con-plasmic tails that trigger conformational changes across formational changes underlying affinity regulation. the plasma membrane ("inside-out" signaling); under certain conditions, ligand binding to the extracellular Results and Discussion domains can trigger an intracellular signal ("outside-in" signaling). Structure Determination We predicted, based on computer docking, that the § To whom correspondence should be addressed (e-mail: rlidding@ burnham-inst.org). glutamic acid side chain of the GFOGER collagen motif




Mejía, E. R., Ospina, J. D., Osorno, L., Márquez, M. A., & Morales, A. L. (2015). Mineralogical Characterization of Chalcopyrite Bioleaching. In Fourier Transform - Signal Processing and Physical Sciences. InTech. https://doi.org/10.5772/59489

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