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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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Protein movements of the iC3b-binding  site in the two structures. Position of the side chains of  residues involved in iC3b  binding on MIDAS relative  to Mn (white ball) in the open  (red) and closed (yellow)  structures. The residues that  are also involved in NIF  binding, G143, D149, E178E,  and R208 (based on single or  double amino acid substitutions) (Rieu et al., 1996), undergo little movement in the  two structures (see also Table II).
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Figure 3: Protein movements of the iC3b-binding site in the two structures. Position of the side chains of residues involved in iC3b binding on MIDAS relative to Mn (white ball) in the open (red) and closed (yellow) structures. The residues that are also involved in NIF binding, G143, D149, E178E, and R208 (based on single or double amino acid substitutions) (Rieu et al., 1996), undergo little movement in the two structures (see also Table II).

Mentions: The residues involved in iC3b binding mapped to the MIDAS face of r11bA, in close proximity to the metal ion (Fig. 3). Two other ligands, NIF and CD54, also require residues expressed on the MIDAS face for interaction with CD11b and CD11a receptors, respectively (Rieu et al., 1994; Huang and Springer, 1995). The divalent cation– dependent interaction of iC3b with CR3 or its isolated r11bA requires key glutamate residues in iC3b (Taniguchi-Sidle and Isenman, 1994). The ring-like arrangement of the iC3b-binding site around the metal ion lends support to our hypothesis that the exogenous metal-coordinating glutamate in the open structure may be a mimic of an integrin interaction with ligand (Lee et al., 1995b). Recent docking of collagen and CD54 ligands on the A-domains of CD49b and CD11a, respectively, showed that the respective glutamates can be accommodated in the A-domain without severe steric clashes, suggesting that the metal ion in the A-domain can coordinate the glutamate “ligands” directly (Emsley et al., 1997; Bella et al., 1998). Co-crystals of the A-domain in complex with activation-dependent and -independent ligands will be required to determine if the metal ion contributes directly to ligand coordination.


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)

Protein movements of the iC3b-binding  site in the two structures. Position of the side chains of  residues involved in iC3b  binding on MIDAS relative  to Mn (white ball) in the open  (red) and closed (yellow)  structures. The residues that  are also involved in NIF  binding, G143, D149, E178E,  and R208 (based on single or  double amino acid substitutions) (Rieu et al., 1996), undergo little movement in the  two structures (see also Table II).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 3: Protein movements of the iC3b-binding site in the two structures. Position of the side chains of residues involved in iC3b binding on MIDAS relative to Mn (white ball) in the open (red) and closed (yellow) structures. The residues that are also involved in NIF binding, G143, D149, E178E, and R208 (based on single or double amino acid substitutions) (Rieu et al., 1996), undergo little movement in the two structures (see also Table II).
Mentions: The residues involved in iC3b binding mapped to the MIDAS face of r11bA, in close proximity to the metal ion (Fig. 3). Two other ligands, NIF and CD54, also require residues expressed on the MIDAS face for interaction with CD11b and CD11a receptors, respectively (Rieu et al., 1994; Huang and Springer, 1995). The divalent cation– dependent interaction of iC3b with CR3 or its isolated r11bA requires key glutamate residues in iC3b (Taniguchi-Sidle and Isenman, 1994). The ring-like arrangement of the iC3b-binding site around the metal ion lends support to our hypothesis that the exogenous metal-coordinating glutamate in the open structure may be a mimic of an integrin interaction with ligand (Lee et al., 1995b). Recent docking of collagen and CD54 ligands on the A-domains of CD49b and CD11a, respectively, showed that the respective glutamates can be accommodated in the A-domain without severe steric clashes, suggesting that the metal ion in the A-domain can coordinate the glutamate “ligands” directly (Emsley et al., 1997; Bella et al., 1998). Co-crystals of the A-domain in complex with activation-dependent and -independent ligands will be required to determine if the metal ion contributes directly to ligand coordination.

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