Endogenously Bound Ligands Crystal Structure of Bovine Cd1b3 With
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Crystal Structure of Bovine CD1b3 with Endogenously Bound Ligands Enrico Girardi, Jing Wang, Thien-Thi Mac, Cees Versluis, Veemal Bhowruth, Gurdyal Besra, Albert J.R. Heck, Ildiko This information is current as Van Rhijn and Dirk M. Zajonc of October 1, 2021. J Immunol published online 2 June 2010 http://www.jimmunol.org/content/early/2010/06/02/jimmun ol.1000042 Downloaded from Supplementary http://www.jimmunol.org/content/suppl/2010/06/02/jimmunol.100004 Material 2.DC1 http://www.jimmunol.org/ Why The JI? Submit online. • Rapid Reviews! 30 days* from submission to initial decision • No Triage! Every submission reviewed by practicing scientists • Fast Publication! 4 weeks from acceptance to publication *average by guest on October 1, 2021 Subscription Information about subscribing to The Journal of Immunology is online at: http://jimmunol.org/subscription Permissions Submit copyright permission requests at: http://www.aai.org/About/Publications/JI/copyright.html Email Alerts Receive free email-alerts when new articles cite this article. Sign up at: http://jimmunol.org/alerts The Journal of Immunology is published twice each month by The American Association of Immunologists, Inc., 1451 Rockville Pike, Suite 650, Rockville, MD 20852 All rights reserved. Print ISSN: 0022-1767 Online ISSN: 1550-6606. Published June 2, 2010, doi:10.4049/jimmunol.1000042 The Journal of Immunology Crystal Structure of Bovine CD1b3 with Endogenously Bound Ligands Enrico Girardi,* Jing Wang,* Thien-Thi Mac,* Cees Versluis,†,‡ Veemal Bhowruth,x Gurdyal Besra,x Albert J.R. Heck,†,‡ Ildiko Van Rhijn,{,‖ and Dirk M. Zajonc* The CD1 family of Ag-presenting molecules is able to display lipids to T cells by binding them within a hydrophobic groove con- nected to the protein surface. In particular, the CD1b isotype is capable of binding ligands with greatly varying alkyl chain lengths through a complex network of interconnected hydrophobic pockets. Interestingly, mycobacterial lipids such as glucose monomy- colate exclusively bind to CD1b. We determined the crystal structure of one of the three expressed bovine CD1b proteins, CD1b3, in complex with endogenous ligands, identified by mass spectrometry as a mixture of phosphatidylcholine and phosphatidylethanol- amine, and analyzed the ability of the protein to bind glycolipids in vitro. The structure reveals a complex binding groove archi- tecture, similar to the human ortholog but with consequential differences. Intriguingly, in bovine CD1b3 only the A’, C’ and F’ Downloaded from pockets are present, whereas the T’ pocket previously described in human CD1b is closed. This different pocket conformation could affect the ability of boCD1b3 to recognize lipids with long acyl chains such as glucose monomycolate. However, even in the absence of a T’ tunnel, bovine CD1b3 is able to bind mycolates from Rhodococcus ruber in vitro. The Journal of Immunology, 2010, 185: 000–000. uberculosis, the disease caused in humans by infection not directly encoded by genes, and the low level of polymorphism with Mycobacterium tuberculosis, represents a major exhibited by the CD1 family of Ag-presenting molecules that dis- http://www.jimmunol.org/ T cause of mortality worldwide, with increasing reports of play these Ags to T cells (3). During mycobacterial infection in multidrug-resistant strains appearing in several countries (1). In humans and animals, CD1-restricted and glycolipid-specific T cell addition, bovine tuberculosis, caused by Mycobacterium bovis, responses can be detected ex vivo, suggesting a physiologically is of economic and zoonotic concern. Unfortunately, the attenuated relevant role for this mode of Ag presentation. Despite the fact that bacillus Calmette-Guerin vaccine currently available is of little pro- all these features would make CD1-presented lipids excellent vac- tective efficacy in humans and animals (2), highlighting the need of cine subunit candidates, the CD1 system is often seen as static, not alternative approaches for the development of an effective vaccine subject to evolutionary pressure exerted by the changing environ- against tuberculosis. In recent years, mycobacterial glycolipid and mental challenges of an evolving species, and often classified as by guest on October 1, 2021 lipid Ags have been the focus of much attention in this context part of the innate immune system. because of the T cell stimulatory activity of these compounds, the CD1 molecules, similar to MHC class I molecules, exist on the stable chemical structure of the lipid backbone, because lipids are surface of APCs as noncovalent heterodimers formed by a CD1 H chain and a b2-microglobulin (b2m) L chain (4). Whereas the b2m chain consists of a single Ig-like domain, the CD1 H chain *Division of Cell Biology, La Jolla Institute for Allergy and Immunology, La Jolla, CA; †Biomolecular Mass Spectrometry and Proteomics Group, Bijvoet Center for Biomo- is anchored to the membrane via a single-pass transmembrane lecular Research and Utrecht Institute for Pharmaceutical Sciences and {Department of domain and contains a short intracellular cytoplasmic tail and Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht Univer- sity; ‡Netherlands Proteomics Centre, Utrecht, The Netherlands; xSchool of Biosciences, three extracellular domains (denominated a1, a2anda3). The College of Life and Environmental Sciences, University of Birmingham, Edgbaston, C-terminal cytoplasmic tail usually contains trafficking motifs ‖ Birmingham, United Kingdom; and Division of Rheumatology, Immunology and Al- responsible for the intracellular localization of the protein (5). lergy, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115 The a1anda2 ectodomains form the Ag-binding groove respon- Received for publication January 8, 2010. Accepted for publication April 16, 2010. sible for the recognition of self and nonself Ags, whereas the This work was supported in part by Grant AI 074952 from the National Institutes of a3 domain associates noncovalently with b2m. The CD1 binding Health (to D.M.Z.). D.M.Z. is the recipient of an investigator award from the Cancer Research Institute. G.S.B. acknowledges support in the form of a Personal Research groove is highly hydrophobic and defined by two a helices that Chair from Mr. James Badrick, Royal Society Wolfson Research Merit Award, as sit above an antiparallel b-sheet platform. Ags are generally a former Lister Institute-Jenner Research Fellow, the Medical Council and The Well- come Trust (084923/B/08/7). I.V.R. is supported by a Meervoud subsidy of the bound with the alkyl chains buried in the deep hydrophobic Nederlandse Organisatie voor Wetenschappelijk Onderzoek. groove, whereas the glycosidic or polar portion of the molecule Structure factors and coordinates presented in this article have been deposited into is exposed at the surface for recognition by a TCR (4). However, the Protein Data Bank database with code 3L9R. while the overall architecture of these Ag-presenting molecules Address correspondence and reprint requests to Dirk M. Zajonc, La Jolla Institute for is conserved, the size, shape, and number of individual pockets Allergy and Immunology, 9420 Athena Circle, La Jolla CA, 92037. E-mail address: differ between the various CD1 isotypes. [email protected] In humans, all group 1 CD1 proteins (CD1a, CD1b, and CD1c) The online version of this article contains supplemental material. are highly expressed on immature thymocytes and immature and Abbreviations used in this paper: b2m, b2-microglobulin; bo, bovine; ESI, electrospray ionization; GMM, glucose monomycolate; huCD1b, human CD1b; mature dendritic cells, whereas group 2 CD1 (CD1d) is expressed IEF, isoelectric focusing; MS, mass spectrometry; PDB, Protein Data Bank; PC, at lower levels on many cell types (3). A fifth CD1 molecule, phosphatidylcholine; PE, phosphatidylethanolamine; pK, negative logarithm of the CD1e, is not expressed on the cell surface but is found to be in- dissociation constant K. volved in facilitating lipid loading onto CD1b (6). CD1d is the Copyright Ó 2010 by The American Association of Immunologists, Inc. 0022-1767/10/$16.00 restricting element for NKT cells, a cell population with a limited www.jimmunol.org/cgi/doi/10.4049/jimmunol.1000042 2 STRUCTURAL BASIS OF LIPID-Ag RECOGNITION IN CATTLE T cell repertoire that can quickly release large amounts of IFN-g for mouse CD1d (24). The protein expressed in insect cells was purified by and other cytokines (7). Group 1 CD1 proteins are known for their Nickel affinity chromatography (HisTrap FF; GE Healthcare, Piscataway, ability to present lipid Ags to T cells with a diverse T cell repertoire NJ) and eluted with a linear gradient of 20–250 mM imidazole, followed by anion-exchange chromatography on a MonoQ 5/50 column (GE Health- (8, 9). Each of the five human CD1 isotypes possesses typical care) equilibrated with 10 mM Tris-HCl (pH 8.0) and elution using a linear characteristics in terms of size and shape of the Ag-binding groove gradient of 0–350 mM NaCl. The fractions containing the boCD1b3-b2m and its subcellular location. This finding has led to the general idea heterodimer were pooled together and further purified by gel filtra- that human group 1 CD1 represents all possible options to present tion on a Superdex200 10/300 column (GE Healthcare) equilibrated in 50 mM HEPES (pH 7.5), 150 mM NaCl. The fractions containing the an optimal variety of lipid Ags to T cells; CD1b, with the largest complex were then concentrated to 10 mg/ml in 10 mM HEPES Ag-binding groove, is the only isotype that can bind mycolates and (pH 7.5), 30 mM NaCl for subsequent crystallization and analysis. uses lysosomal factors to present exogenous Ags; CD1a has the smallest groove and functions without intersecting with the lyso- Mass spectrometry analysis of boCD1b3 some, whereas CD1c is intermediate in both regards (10, 11). Be- The intact noncovalent complex of boCD1b3 with the lipids was analyzed cause all CD1 molecules except CD1d have been deleted in muroid with native nano electrospray ionization (ESI) mass spectrometry (MS) rodents, the human family of CD1 proteins is often considered to be using borosilicate capillaries to introduce the sample.