The 2.7 Å Crystal Structure of the Autoinhibited Human c-Fms Kinase Domain Mark Walter 1 †, Isabelle S. Lucet 1 †, Onisha Patel 1 Sophie E. Broughton 1 , Rebecca Bamert 1 , Neal K. Williams 1,2 Emmanuelle Fantino 2 , Andrew F. Wilks 2 ⁎ and Jamie Rossjohn 1 ⁎ 1 Protein Crystallography Unit, Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Monash University, Clayton, Victoria 3800, Australia 2 Cytopia Research Pty Ltd, Baker Heart Research Institute, Commercial Road, Melbourne, Victoria 3004, Australia c-Fms, a member of the Platelet-derived Growth Factor (PDGF) receptor family of receptor tyrosine kinases (RTKs), is the receptor for macrophage colony stimulating factor (CSF-1) that regulates proliferation, differentiation and survival of cells of the mononuclear phagocyte lineage. Abnormal expression of c-fms proto-oncogene is associated with a significant number of human pathologies, including a variety of cancers and rheumatoid arthritis. Accordingly, c-Fms represents an attractive therapeutic target. To further understand the regulation of c-Fms, we determined the 2.7 Å resolution crystal structure of the cytosolic domain of c-Fms that comprised the kinase domain and the juxtamembrane domain. The structure reveals the crucial inhibitory role of the juxtamembrane domain (JM) that binds to a hydrophobic site immediately adjacent to the ATP binding pocket. This interaction prevents the activation loop from adopting an active conforma- tion thereby locking the c-Fms kinase into an autoinhibited state. As observed for other members of the PDGF receptor family, namely c-Kit and Flt3, three JM-derived tyrosine residues primarily drive the mechanism for autoinhibition in c-Fms, therefore defining a common autoinhibitory mechanism within this family. Moreover the structure provides an understanding of c-Fms inhibition by Gleevec as well as providing a platform for the development of more selective inhibitors that target the inactive conformation of c-Fms kinase. © 2007 Elsevier Ltd. All rights reserved. *Corresponding authors Keywords: macrophage colony stimulating factor receptor; c-Fms; receptor tyrosine kinase; autoinhibitory mechanism; Gleevec Introduction Receptor and non-receptor protein kinases (PTKs) are a large family of signalling molecules that play a fundamental physiological role within the cell. Accordingly, the cellular activity of PTKs is tightly regulated at the onset of cellular signalling, with most PTKs containing specific modular domains that maintain the PTK in an inactive state. For example, within the non-receptor PTK family, the SH2-SH3 domains regulate the activity of the Src kinases 1,2 and Abl kinase, 3 whereas a kinase-like domain regulates the activity of the Janus kinase PTK domain. 4 Others, including the Platelet-derived Growth Factor (PDGF) RTK family possess a regu- latory intracellular juxtamembrane (JM) domain that abuts their PTK domain. The PDGF receptor family includes the macro- phage colony stimulating factor receptor, (CSF-1 receptor or c-Fms), the Fms-like tyrosine kinase (Flt3), platelet-derived growth factor receptors α and β (PDGFRα and PDGFRβ), and the stem cell factor receptor (c-Kit). This family of kinases is † M. W. and I. L. contributed equally to this work. Abbreviations used: PTK, protein tyrosine kinase; PDGF, Platelet-derived Growth Factor; RTK, receptor tyrosine kinase; JM, juxtamembrane domain; c-Fms, macrophage colony stimulating factor receptor; KID, kinase insert domain; DFSP, dermatofibrosarcoma protuberans; GISTs, gastrointestinal stromal tumours; r.m.s.d., root-mean-square deviation; PDB, Protein Data Bank. E-mail addresses of the corresponding authors: Andrew.Wilks@cytopia.com.au; Jamie.Rossjohn@med.monash.edu.au doi:10.1016/j.jmb.2007.01.036 J. Mol. Biol. (2007) 367, 839–847 0022-2836/$ - see front matter © 2007 Elsevier Ltd. All rights reserved.