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Two functional states of the CD11b A-domain: correlations with key features of two Mn2+-complexed crystal structures.

Li R, Rieu P, Griffith DL, Scott D, Arnaout MA - J. Cell Biol. (1998)

Bottom Line: Approximately 10% of wild-type CD11b A-domain is present in an "active" state (binds to activation-dependent ligands, e.g., iC3b and the mAb 7E3).In the isolated domain and in the holoreceptor, the percentage of the active form can be quantitatively increased or abolished in F302W and T209A mutants, respectively.The iC3b-binding site is located on the MIDAS face and includes conformationally sensitive residues that undergo significant shifts in the open versus closed structures.

View Article: PubMed Central - PubMed

Affiliation: Leukocyte Biology and Inflammation Program, Renal Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129, USA.

ABSTRACT
In the presence of bound Mn2+, the three- dimensional structure of the ligand-binding A-domain from the integrin CR3 (CD11b/CD18) is shown to exist in the "open" conformation previously described only for a crystalline Mg2+ complex. The open conformation is distinguished from the "closed" form by the solvent exposure of F302, a direct T209-Mn2+ bond, and the presence of a glutamate side chain in the MIDAS site. Approximately 10% of wild-type CD11b A-domain is present in an "active" state (binds to activation-dependent ligands, e.g., iC3b and the mAb 7E3). In the isolated domain and in the holoreceptor, the percentage of the active form can be quantitatively increased or abolished in F302W and T209A mutants, respectively. The iC3b-binding site is located on the MIDAS face and includes conformationally sensitive residues that undergo significant shifts in the open versus closed structures. We suggest that stabilization of the open structure is independent of the nature of the metal ligand and that the open conformation may represent the physiologically active form.

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The Mn2+ structure  of r11bA. A and B show a  close-up of the MIDAS motif  in the open (this report) and  closed (Lee et al., 1995a) conformations, respectively. The  Mn2+ metal ion in both forms  is displayed in gray, oxygen  atoms and water molecules  are in red, and the protein  backbone is shown schematically as a light green ribbon.  C and D show a top view of  r11bA structure (ribbon backbone) with the major changes  in the open (C) (this report)  and closed (D) Mn2+-complexed conformations. The solvent-exposed Mn2+ is shown  (light green ball) surrounded  by the largely buried metal  coordinating residues D140,  S142, S144, T209, and D242  (side chains are outlined in  yellow and red). F302 and  F275 are shown in light blue.  The figure was built using  QUANTA (Molecular Simulations Inc., Mountain View,  CA). See the text for details.
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Figure 1: The Mn2+ structure of r11bA. A and B show a close-up of the MIDAS motif in the open (this report) and closed (Lee et al., 1995a) conformations, respectively. The Mn2+ metal ion in both forms is displayed in gray, oxygen atoms and water molecules are in red, and the protein backbone is shown schematically as a light green ribbon. C and D show a top view of r11bA structure (ribbon backbone) with the major changes in the open (C) (this report) and closed (D) Mn2+-complexed conformations. The solvent-exposed Mn2+ is shown (light green ball) surrounded by the largely buried metal coordinating residues D140, S142, S144, T209, and D242 (side chains are outlined in yellow and red). F302 and F275 are shown in light blue. The figure was built using QUANTA (Molecular Simulations Inc., Mountain View, CA). See the text for details.

Mentions: The structure of r11bA crystallized in the presence of Mn2+ is nearly identical to that of the Mg2+ form (Lee et al., 1995b). The bound manganese ion is located in a shallow crevice at the top of the internal β sheet where it is coordinated by S142, S144, T209, and two water molecules. The sixth Mn2+ coordination site is provided by the side chain of E314 from a neighboring A-domain within the crystal lattice (Fig. 1 A). These structures are referred to as adopting the open conformation since F275 and F302 are solvent exposed (Fig. 1 C). The closed conformation (burial of F302, F275, or their equivalents into the hydrophobic core of the protein, a break in the T209 [or equivalent threonine]–metal bond; Fig. 1, B and D) and a corresponding change in surface charge and topology of MIDAS (Lee et al., 1995a,b; Qu and Leahy, 1995; Qu and Leahy, 1996; Emsley et al., 1997; Baldwin et al., 1998) are found in all remaining integrin A-domain structures determined to date. This includes the Mn2+ and no-metal forms of CD11bA, Mn2+ and Mg2+ forms of CD11aA, and a Mg2+-complexed form of CD49bA. Taken together, these findings suggest that the integrin A-domain exists primarily in two conformations, the formation of which is unaffected by the nature of the metal ion in the active site or the experimental conditions of protein purification and crystal growth.


Two functional states of the CD11b A-domain: correlations with key features of two Mn2+-complexed crystal structures.

Li R, Rieu P, Griffith DL, Scott D, Arnaout MA - J. Cell Biol. (1998)

The Mn2+ structure  of r11bA. A and B show a  close-up of the MIDAS motif  in the open (this report) and  closed (Lee et al., 1995a) conformations, respectively. The  Mn2+ metal ion in both forms  is displayed in gray, oxygen  atoms and water molecules  are in red, and the protein  backbone is shown schematically as a light green ribbon.  C and D show a top view of  r11bA structure (ribbon backbone) with the major changes  in the open (C) (this report)  and closed (D) Mn2+-complexed conformations. The solvent-exposed Mn2+ is shown  (light green ball) surrounded  by the largely buried metal  coordinating residues D140,  S142, S144, T209, and D242  (side chains are outlined in  yellow and red). F302 and  F275 are shown in light blue.  The figure was built using  QUANTA (Molecular Simulations Inc., Mountain View,  CA). See the text for details.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132978&req=5

Figure 1: The Mn2+ structure of r11bA. A and B show a close-up of the MIDAS motif in the open (this report) and closed (Lee et al., 1995a) conformations, respectively. The Mn2+ metal ion in both forms is displayed in gray, oxygen atoms and water molecules are in red, and the protein backbone is shown schematically as a light green ribbon. C and D show a top view of r11bA structure (ribbon backbone) with the major changes in the open (C) (this report) and closed (D) Mn2+-complexed conformations. The solvent-exposed Mn2+ is shown (light green ball) surrounded by the largely buried metal coordinating residues D140, S142, S144, T209, and D242 (side chains are outlined in yellow and red). F302 and F275 are shown in light blue. The figure was built using QUANTA (Molecular Simulations Inc., Mountain View, CA). See the text for details.
Mentions: The structure of r11bA crystallized in the presence of Mn2+ is nearly identical to that of the Mg2+ form (Lee et al., 1995b). The bound manganese ion is located in a shallow crevice at the top of the internal β sheet where it is coordinated by S142, S144, T209, and two water molecules. The sixth Mn2+ coordination site is provided by the side chain of E314 from a neighboring A-domain within the crystal lattice (Fig. 1 A). These structures are referred to as adopting the open conformation since F275 and F302 are solvent exposed (Fig. 1 C). The closed conformation (burial of F302, F275, or their equivalents into the hydrophobic core of the protein, a break in the T209 [or equivalent threonine]–metal bond; Fig. 1, B and D) and a corresponding change in surface charge and topology of MIDAS (Lee et al., 1995a,b; Qu and Leahy, 1995; Qu and Leahy, 1996; Emsley et al., 1997; Baldwin et al., 1998) are found in all remaining integrin A-domain structures determined to date. This includes the Mn2+ and no-metal forms of CD11bA, Mn2+ and Mg2+ forms of CD11aA, and a Mg2+-complexed form of CD49bA. Taken together, these findings suggest that the integrin A-domain exists primarily in two conformations, the formation of which is unaffected by the nature of the metal ion in the active site or the experimental conditions of protein purification and crystal growth.

Bottom Line: Approximately 10% of wild-type CD11b A-domain is present in an "active" state (binds to activation-dependent ligands, e.g., iC3b and the mAb 7E3).In the isolated domain and in the holoreceptor, the percentage of the active form can be quantitatively increased or abolished in F302W and T209A mutants, respectively.The iC3b-binding site is located on the MIDAS face and includes conformationally sensitive residues that undergo significant shifts in the open versus closed structures.

View Article: PubMed Central - PubMed

Affiliation: Leukocyte Biology and Inflammation Program, Renal Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129, USA.

ABSTRACT
In the presence of bound Mn2+, the three- dimensional structure of the ligand-binding A-domain from the integrin CR3 (CD11b/CD18) is shown to exist in the "open" conformation previously described only for a crystalline Mg2+ complex. The open conformation is distinguished from the "closed" form by the solvent exposure of F302, a direct T209-Mn2+ bond, and the presence of a glutamate side chain in the MIDAS site. Approximately 10% of wild-type CD11b A-domain is present in an "active" state (binds to activation-dependent ligands, e.g., iC3b and the mAb 7E3). In the isolated domain and in the holoreceptor, the percentage of the active form can be quantitatively increased or abolished in F302W and T209A mutants, respectively. The iC3b-binding site is located on the MIDAS face and includes conformationally sensitive residues that undergo significant shifts in the open versus closed structures. We suggest that stabilization of the open structure is independent of the nature of the metal ligand and that the open conformation may represent the physiologically active form.

Show MeSH
Related in: MedlinePlus