title: Room temperature structure of human IgG4-Fc from crystals analysed in situ.
abstract: The Fc region of IgG antibodies (Cγ2 and Cγ3 domains) is responsible for effector functions such as antibody-dependent cell-mediated cytotoxicity and phagocytosis, through engagement with Fcγ receptors, although the ability to elicit these functions differs between the four human IgG subclasses. A key determinant of Fcγ receptor interactions is the FG loop in the Cγ2 domain. High resolution cryogenic IgG4-Fc crystal structures have revealed a unique conformation for this loop, which could contribute to the particular biological properties of this subclass. To further explore the conformation of the IgG4 Cγ2 FG loop at near-physiological temperature, we solved a 2.7Å resolution room temperature structure of recombinant human IgG4-Fc from crystals analysed in situ. The Cγ2 FG loop in one chain differs from the cryogenic structure, and adopts the conserved conformation found in IgG1-Fc; however, this conformation participates in extensive crystal packing interactions. On the other hand, at room temperature, and free from any crystal packing interactions, the Cγ2 FG loop in the other chain adopts the conformation previously observed in the cryogenic IgG4-Fc structures, despite both conformations being accessible. The room temperature human IgG4-Fc structure thus provides a more complete and physiologically relevant description of the conformation of this functionally critical Cγ2 FG loop.
authors.affiliation: King's College London, Randall Division of Cell and Molecular Biophysics, New Hunt's House, London SE1 1UL, United Kingdom; Medical Research Council & Asthma UK Centre in Allergic Mechanisms of Asthma, London, United Kingdom. Electronic address: anna.davies@kcl.ac.uk.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Davies
authors.affiliation: Sanquin Research, Amsterdam 1066 CX, The Netherlands; University of Amsterdam, Academic Medical Centre Landsteiner Laboratory, The Netherlands.
authors.forename: Theo
authors.initials: T
authors.lastname: Rispens
authors.affiliation: Sanquin Research, Amsterdam 1066 CX, The Netherlands; University of Amsterdam, Academic Medical Centre Landsteiner Laboratory, The Netherlands.
authors.forename: Pleuni
authors.initials: P
authors.lastname: Ooijevaar-de Heer
authors.affiliation: Sanquin Research, Amsterdam 1066 CX, The Netherlands; University of Amsterdam, Academic Medical Centre Landsteiner Laboratory, The Netherlands.
authors.forename: Rob C
authors.initials: RC
authors.lastname: Aalberse
authors.affiliation: King's College London, Randall Division of Cell and Molecular Biophysics, New Hunt's House, London SE1 1UL, United Kingdom; Medical Research Council & Asthma UK Centre in Allergic Mechanisms of Asthma, London, United Kingdom. Electronic address: brian.sutton@kcl.ac.uk.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Sutton
mesh_terms: D018360:Crystallography, X-Ray; D006801:Humans; D007141:Immunoglobulin Fc Fragments / Q000737:chemistry*; D007074:Immunoglobulin G / Q000737:chemistry*; D011487:Protein Conformation; D013696:Temperature
chemical_list: D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G
keywords: Antibody; IgG4; Immunoglobulin; X-ray crystallography