Biomedical Engineering Reference
In-Depth Information
16.6.1.1
Dimeric
-
Transmembrane Domain of the T Cell Receptor
In 2006, Call et al. solved the first atomic-scale NMR structure of a detergent-
reconstituted
transmembrane domain homodimer (residue 7-39) of the T cell
receptor complex [ 51 ]. The NMR structure revealed extensive helix-helix contacts
along the transmembrane interface, which are responsible for the formation of the
left-handed coiled-coil dimer. This inter-helical packing was confirmed in 2007, by
Douglas et al. who used the DNA-nanotube liquid crystal for the first time to align
the
-
-
transmembrane domain of the T cell receptor [ 11 ]. In the 2007 experiment,
the
membrane protein was reconstituted in mixed negative detergent micelles
(5:1 M ratio of dodecylphosphorylcholine and dodecylsulfate) and aligned in the
presence of DNA nanotubes to enable accurate measurement of backbone N H and
C ' H ' RDCs. The measured 1 H- 15 Nand 1 H ' - 13 C ' RDCs confirmed the helix orien-
tation and agrees very well with the known NMR structure of the
-
transmembrane
domain, with a correlation coefficient of the singular value decomposition fit of 0.98,
which is the normalized root mean square difference between experimental RDCs
and the RDCs predicted independently by the structural model (Fig. 16.4 b).
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16.6.1.2
Dimeric and Trimeric Assembly of the NKG2C-DAP12
Transmembrane Complex
In 2010, Call et al. provided the structure of another functionally homologous
transmembrane-signaling dimer, DAP12, both alone and covalently linked to a
receptor transmembrane domain, NKG2C-DAP12 trimeric transmembrane peptide
complex [ 52 ]. The structure of the DAP12 dimer revealed a similar arrangement
as observed in the
transmembrane structure. The major new feature observed
in the DAP12 transmembrane dimer structure was the presence of a threonine
residue that forms an intra-helical hydrogen bond to a conserved aspartic acid,
a feature that turned out to be critical for the correct assembly of the receptor
transmembrane domains. DNA-nanotube liquid crystal was used to enable the
measurement of 1 H- 15 Nand 1 H ' - 13 C ' RDCs for DAP12 reconstituted in mixed
tetradecylphosphorylcholine and dodecylsulfate detergent micelles, both alone and
with a receptor transmembrane domain in an assembled trimeric complex model as
shown in Fig. 16.4 c. Applied RDCs data were combined with NOEs to refine the
NMR solution structure, which ultimately confirmed the inter-helical packing of the
dimer and the assembled trimeric complex model. The measured RDCs agree very
well with a correlation coefficient of the singular value decomposition fit of 0.97
(data not published).
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16.6.2
Channels and Membrane Transporters
Channels and membrane transporters govern cellular influx and efflux of ions, small
molecules, nutrients, macromolecules, and drugs across biological membranes.
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