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A Transmembrane Domain GGxxG Motif in CD4 Contributes to Its Lck-Independent Function but Does Not Mediate CD4 Dimerization.

Parrish HL, Glassman CR, Keenen MM, Deshpande NR, Bronnimann MP, Kuhns MS - PLoS ONE (2015)

Bottom Line: CD4 interactions with class II major histocompatibility complex (MHC) molecules are essential for CD4+ T cell development, activation, and effector functions.Here we show that introducing bulky side-chains into this patch (GGxxG to GVxxL) impairs the Lck-independent role of CD4 in T cell activation upon TCR engagement of agonist and weak agonist stimulation.This suggests that the CD4 transmembrane domain is either mediating interactions with an unidentified partner, or mediating some other function such as membrane domain localization that is important for its role in T cell activation.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunobiology, The University of Arizona College of Medicine, Tucson, Arizona, United States of America.

ABSTRACT
CD4 interactions with class II major histocompatibility complex (MHC) molecules are essential for CD4+ T cell development, activation, and effector functions. While its association with p56lck (Lck), a Src kinase, is important for these functions CD4 also has an Lck-independent role in TCR signaling that is incompletely understood. Here, we identify a conserved GGxxG motif in the CD4 transmembrane domain that is related to the previously described GxxxG motifs of other proteins and predicted to form a flat glycine patch in a transmembrane helix. In other proteins, these patches have been reported to mediate dimerization of transmembrane domains. Here we show that introducing bulky side-chains into this patch (GGxxG to GVxxL) impairs the Lck-independent role of CD4 in T cell activation upon TCR engagement of agonist and weak agonist stimulation. However, using Forster's Resonance Energy Transfer (FRET), we saw no evidence that these mutations decreased CD4 dimerization either in the unliganded state or upon engagement of pMHC concomitantly with the TCR. This suggests that the CD4 transmembrane domain is either mediating interactions with an unidentified partner, or mediating some other function such as membrane domain localization that is important for its role in T cell activation.

No MeSH data available.


The CD4 TMD contains highly conserved glycine residues.(A) CD4 transmembrane domain (TMD) sequence alignment showing highly conserved glycine residues shaded red. (B) Ribbon diagram model or (C) space-filled model of the CD4 TMD with alanine and glycine residues of interest highlighted in magenta (generated with PyMol).
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pone.0132333.g001: The CD4 TMD contains highly conserved glycine residues.(A) CD4 transmembrane domain (TMD) sequence alignment showing highly conserved glycine residues shaded red. (B) Ribbon diagram model or (C) space-filled model of the CD4 TMD with alanine and glycine residues of interest highlighted in magenta (generated with PyMol).

Mentions: The GGxxG sequence in the CD4 transmembrane domain (TMD) represents one such motif (Fig 1A). The spacing of the glycines forms a side-chain free patch along one side of the TMD α-helix that allows tight packing of helices and possibly hydrogen bonding between peptide backbones of TMDs. Such patches have been reported to mediate homotypic or heterotypic interactions in a wide assortment of transmembrane proteins, including glycophorin A (GpA), scavenger receptor class B, type I (SRBI), and the human papilloma virus L2 transmembrane domain [16–18]. The conservation of this sequence in the CD4 TMD of a wide range of vertebrates suggested to us that it might play an important role in T cell activation (Fig 1A).


A Transmembrane Domain GGxxG Motif in CD4 Contributes to Its Lck-Independent Function but Does Not Mediate CD4 Dimerization.

Parrish HL, Glassman CR, Keenen MM, Deshpande NR, Bronnimann MP, Kuhns MS - PLoS ONE (2015)

The CD4 TMD contains highly conserved glycine residues.(A) CD4 transmembrane domain (TMD) sequence alignment showing highly conserved glycine residues shaded red. (B) Ribbon diagram model or (C) space-filled model of the CD4 TMD with alanine and glycine residues of interest highlighted in magenta (generated with PyMol).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493003&req=5

pone.0132333.g001: The CD4 TMD contains highly conserved glycine residues.(A) CD4 transmembrane domain (TMD) sequence alignment showing highly conserved glycine residues shaded red. (B) Ribbon diagram model or (C) space-filled model of the CD4 TMD with alanine and glycine residues of interest highlighted in magenta (generated with PyMol).
Mentions: The GGxxG sequence in the CD4 transmembrane domain (TMD) represents one such motif (Fig 1A). The spacing of the glycines forms a side-chain free patch along one side of the TMD α-helix that allows tight packing of helices and possibly hydrogen bonding between peptide backbones of TMDs. Such patches have been reported to mediate homotypic or heterotypic interactions in a wide assortment of transmembrane proteins, including glycophorin A (GpA), scavenger receptor class B, type I (SRBI), and the human papilloma virus L2 transmembrane domain [16–18]. The conservation of this sequence in the CD4 TMD of a wide range of vertebrates suggested to us that it might play an important role in T cell activation (Fig 1A).

Bottom Line: CD4 interactions with class II major histocompatibility complex (MHC) molecules are essential for CD4+ T cell development, activation, and effector functions.Here we show that introducing bulky side-chains into this patch (GGxxG to GVxxL) impairs the Lck-independent role of CD4 in T cell activation upon TCR engagement of agonist and weak agonist stimulation.This suggests that the CD4 transmembrane domain is either mediating interactions with an unidentified partner, or mediating some other function such as membrane domain localization that is important for its role in T cell activation.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunobiology, The University of Arizona College of Medicine, Tucson, Arizona, United States of America.

ABSTRACT
CD4 interactions with class II major histocompatibility complex (MHC) molecules are essential for CD4+ T cell development, activation, and effector functions. While its association with p56lck (Lck), a Src kinase, is important for these functions CD4 also has an Lck-independent role in TCR signaling that is incompletely understood. Here, we identify a conserved GGxxG motif in the CD4 transmembrane domain that is related to the previously described GxxxG motifs of other proteins and predicted to form a flat glycine patch in a transmembrane helix. In other proteins, these patches have been reported to mediate dimerization of transmembrane domains. Here we show that introducing bulky side-chains into this patch (GGxxG to GVxxL) impairs the Lck-independent role of CD4 in T cell activation upon TCR engagement of agonist and weak agonist stimulation. However, using Forster's Resonance Energy Transfer (FRET), we saw no evidence that these mutations decreased CD4 dimerization either in the unliganded state or upon engagement of pMHC concomitantly with the TCR. This suggests that the CD4 transmembrane domain is either mediating interactions with an unidentified partner, or mediating some other function such as membrane domain localization that is important for its role in T cell activation.

No MeSH data available.