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Structural basis of the leukocyte integrin Mac-1 I-domain interactions with the platelet glycoprotein Ib

Morgan, Juliet; Saleem, Muhammad; Ng, Ruiqi; Armstrong, Caroline; Wong, Szu S.; Caulton, Simon G.; Fickling, Alice; Williams, Huw E.L.; Munday, Adam D.; Lopez, Jose A.; Searle, Mark S.; Emsley, Jonas

Authors

Juliet Morgan

Muhammad Saleem

Ruiqi Ng

Caroline Armstrong

Szu S. Wong

Simon G. Caulton

Alice Fickling

Huw E.L. Williams

Adam D. Munday

Jose A. Lopez

Mark S. Searle

Jonas Emsley



Abstract

Cell-surface receptor interactions between leukocyte integrin macrophage-1 antigen (Mac-1, also known as CR3, aMb2, CD11b/CD18) and platelet glycoprotein Iba (GPIba) are critical to vascular inflammation. To define the key residues at the binding interface, we used nuclear magnetic resonance (NMR) to assign the spectra of the mouse Mac-1 I-domain and mapped the residues contacting the mouse GPIba N-terminal domain (GPIbaN) to the locality of the integrin metal ion-dependant adhesion site (MIDAS) surface. We next determined the crystal structures of the mouse GPIbaN and Mac-1 I-domain to 2 ˚A and 2.5 ˚A resolution, respectively. The mouse Mac-1 I-domain crystal structure reveals an active conformation that is stabilized by a crystal contact from the a7-helix with a glutamatesidechaincompletingtheoctahedralcoordinationsphereoftheMIDASMg21 ion. The amino acid sequence of the a7-helix and disposition of the glutamic acid matches the C-terminal capping region a-helix of GPIba effectively acting as a ligand mimetic. Using these crystal structures in combination with NMR measurements and docking analysis, we developed a model whereby an acidic residue from the GPIba leucine-rich repeat (LRR) capping a-helix coordinates directly to the Mac-1 MIDAS Mg21 ion. The Mac-1:GPIbaN complex involves additional interactions consolidated by an elongated pocket flanking the GPIbaN LRR capping a-helix. The GPIbaN a-helix has an HxxxE motif, which is equivalent by homology to RxxxD from the human GPIbaN. Subsequent mutagenesis of residues at this interface, coupled with surface plasmon resonance studies, confirmed the importance of GPIbaN residues H218, E222, and the Mac-1 MIDAS residue T209 to formation of the complex.

Journal Article Type Article
Publication Date May 14, 2019
Electronic ISSN 2473-9529
Publisher American Society of Hematology
Peer Reviewed Peer Reviewed
Volume 3
Issue 9
Pages 1450-1459
APA6 Citation Morgan, J., Saleem, M., Ng, R., Armstrong, C., Wong, S. S., Caulton, S. G., …Emsley, J. (2019). Structural basis of the leukocyte integrin Mac-1 I-domain interactions with the platelet glycoprotein Ib. Blood Advances, 3(9), 1450-1459. doi:10.1182/bloodadvances.2018027011
DOI https://doi.org/10.1182/bloodadvances.2018027011
Publisher URL http://www.bloodadvances.org/content/3/9/1450
Additional Information This research was originally published in Blood Advances. Structural basis of the leukocyte integrin Mac-1 I-domain interactions with the platelet glycoprotein Ib, Juliet Morgan, Muhammad Saleem, Ruiqi Ng, Caroline Armstrong, Szu S. Wong, Simon G. Caulton, Alice Fickling, Huw E. L. Williams, Adam D. Munday, José A. López, Mark S. Searle and Jonas Emsley, Blood Adv. 2019 May 14;3(9):1450-1459. © the American Society of Hematology.

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